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1、 Technology guide and overview General CONTENTS 3 Introduction 5 Traditional preservation technologies 6 An overview of non-traditional preservation technologies 8 Ohmic 11 Microwave 15 Radio frequency heating 18 High-Pressure Processing 23 Ultra High-Pressure Homogenization 28 Ultraviolet light 33
2、Irradiation 38 Microfiltration 44 Ultrasound 49 Hydrodynamic cavitation 52 Pulsed electric field 58 Ozone 61 Supercritical carbon dioxide 66 Cold plasma 69 Moving forward together 71 References 3 General INTRODUCTION Who is this technology guide for?This technology guide is for anyone looking for a
3、consolidated overview of different preservation technologies with possible benefits and limitations,based mainly on public information such as scientific articles and conference presentations,but in many cases supplemented by our own trials and technical studies.Why should we study a wide range of p
4、reservation technologies?Heat treatment has been used for 100 years on an industrial scale to preserve food for human consumption,extending shelf life and securing food safety.These traditional or conventional heat treatments include autoclaves,as well as continuous indirect heat treatment with hot
5、water and direct heat treatment with steam injection and infusion technology.Non-traditional preservation technologies use many different methods:electric heating,pressure treatments,microwaves,radiation,ultrasound,filtration,gaseous treatments and more.Some of them are thermal processes,and some ar
6、e non-thermal in nature.A few of these methods have reached commercial status in parts of our industry,but many remain experimental,or are confined for a variety of reasons to only limited types of foods.Different methods are suitable for products with different characteristics,such as particulate p
7、roducts,non-particulate products,products sensitive to heat,etc.Others might involve complex equipment or create large energy burdens.There are many technologies out there,and there is a good deal of publicity and opinions from manufacturers and food technologists about the pros and cons of individu
8、al innovations,as well as how they can be applied to one corner or another of the food processing industry.In many cases,it is hard to distinguish facts from opinions,especially when discussing only a single technology at a time.This booklet takes an independent and neutral view of non-traditional p
9、reservation technologies,creating both a guide and a reference for those who are conducting their own evaluations.We provide a practical overview and evaluation of 14 of the most prominent technologies,describing:How they work Their microbiological and chemical effects How far they have been commerc
10、ialized Their potential advantages and disadvantages Their suitability for particular segments or product types Their cost and environmental profiles,when known 4 General This technology guide is based on:A thorough review of the published literature Independent evaluations and tests run in Tetra Pa
11、k laboratories and external pilot centres Information available publicly from technology suppliers Conference presentations Tetra Pak takes an independent and neutral role in this area,based on research and evaluation projects,both alone and with partners,in order to arrive at a more factual basis f
12、or technology choices.In most cases,we do not yet commercially use the technologies in question;in others,we have evaluated them in practical settings.In order to grow within the food and beverage industry we continuously explore and scout for new innovations in the market.This booklet is one way to
13、 increase awareness but also to raise the level of dialogue about what systems are possible and beneficial.Given the rapid development of many technologies,any overview of this scope is necessarily just a snapshot.Tetra Pak monitors developments in this area and aims to update this material as new f
14、indings emerge.In the meantime,if you have specific needs or technical questions,please contact Jeanette Lindau().5 General TRADITIONAL PRESERVATION TECHNOLOGIES Heat treatment is one of the most common methods of food preservation.It concerns deactivation of enzymes and destruction of microorganism
15、s,both for food quality and food safety reason.The most dominating method of continuous heat treatment is based on heat being transferred directly from steam or indirectly from hot water via heat exchangers.Heating the food to temperatures of 60-100C for a few seconds to minutes is called pasteuriza
16、tion.A pasteurization process(thermal or non-thermal)should give 5-log reductions on the most pertinent pathogenic organism(for the applied process)likely to be present in the food(FDA).Sterilization requires higher heating temperatures,and leads to the absence of microorganisms capable of growing i
17、n the food at normal nonrefrigerated conditions at which the food is likely to be held during manufacture,distribution and storage(Codex Alimentarius).Normally 135-140C for a few seconds are used in an aseptic process leading to a commercially sterile product.The retort and canning industry use ster
18、ilizing in a container at 115-130C for 20-30 min.Problems and challenges There is an increased interest in developing new preservation technologies due to the fast-growing consumer demands for food products that are perceived as more natural and healthier.There is also an increased interest in lower
19、ing the environmental impact of food processing.Products that are very heat-sensitive might need non-thermal inactivation of microorganisms.Therefore,processing techniques have been developed that are“gentler”or “less severe”.6 General AN OVERVIEW OF NON-TRADITIONAL PRESERVATION TECHNOLOGIES Most no
20、n-traditional technologies aim to be equivalent to traditional thermal pasteurization conditions,which means cold distribution.None of these technologies have the potential for achieving commercial sterility with ambient distributed products unless they are combined with heat or based on heat as an
21、inactivation process.The development level of these technologies varies,and many are in the research stage.All processes need to be validated and verified to ensure that critical processing limits are established,and no public health risk is present for the products produced.More studies are require
22、d on some of them before their use is accepted as safe processing and legally accepted.These technologies can be divided into thermal and non-thermal categories,and further subdivided.The non-traditional thermal technologies add heat to the product in a different way than conventional methods.These
23、are sometimes referred to as“advanced heating technologies”in the literature.Thermal Ohmic heating An electric current is passed through the food via electrodes,and heating occurs due to the electrical resistance of the food.The critical parameters are time and temperature.Microwave heating Electrom
24、agnetic waves at certain frequencies(915 MHz and 2450 MHz)are used to generate heat in the food.Heating of material occurs due to interaction of the electric field of the microwave with charged particles and molecules in the material.The critical parameters are time and temperature.Radiofrequency Th
25、e electromagnetic field in the range of 1-300 MHz is used to heat the food.Heating of the material occurs due to interaction of the electric field with charged particles and molecules in the material.The critical parameters are time and temperature.Non-thermal Pressure High-Pressure Processing The p
26、roduct is subjected to very high static pressures(300MPa).The food packages are loaded into a vessel and pressure is transmitted via water.The critical parameters are time and pressure.Ultra-High-Pressure Homogenization A continuous process where the fluid is forced through a high-pressure valve,usi
27、ng dynamic high pressures in the range of 200 MPa to 400 MPa.A non-thermal process,in that no heat is added on purpose.7 General Radiation Ultraviolet light Radiation from the ultraviolet region(100-400 nm)or more specifically the UVC(200-280 nm)is used for disinfection.UVC light induces mutations i
28、n the DNA of the microorganism.The critical parameter is UVC dose.Irradiation A non-thermal process that exposes pre-packaged or bulk foodstuffs to gamma rays,x-rays or electrons.The critical parameter is radiation dose.Physical removal Microfiltration A non-thermal treatment based on physical remov
29、al of microorganisms using a porous membrane.Cavitation Ultrasound Uses energy generated by sound waves to create cavitation,which has a bactericidal effect.A non-thermal process,since no heat is added on purpose.Hydrodynamic cavitation Uses cavitation generated by the passage of the liquid through
30、a constriction.A non-thermal process,since no heat is added on purpose.Other Pulsed Electric Field A non-thermal process.The food is in contact with electrodes,one being high voltage and one ground,and is treated with short electrical pulses(s)at high electrical voltage(30-40 kV/cm).Critical paramet
31、ers are electric field strength,pulse frequency and shape and initial product temperature.Ozone A non-thermal gaseous treatment of the food.Ozone is a strong antimicrobial agent,with an oxidation-reduction potential higher than that of chlorine.Supercritical carbon dioxide A non-thermal gaseous trea
32、tment in which supercritical carbon dioxide comes in contact with the product at elevated pressures.Cold plasma A non-thermal treatment.Plasma is the fourth state of matter and is an electrically energized matter in a gaseous state composed of photons,charged particles,free radicals as well as atoms
33、 in their fundamental or excited states with a net neutral charge.8 General OHMIC Other names Joule heating,electroconductive heating,electrical resistance heating and electro heating Process an electric current is passed through the food and heating occurs due to the electrical resistance of the fo
34、od.Effect The most resistant pathogenic microorganism is most likely the same as for thermal processes.There is no data found on any organism with an unusual resistance to ohmic heating.No difference in chemical effect compared to conventional heating.Advantages Simultaneous,rapid,heating of liquid
35、and particles(volumetric heating).Low fouling,since no hot surfaces.Disadvantages High demand on electric power supply.Homogenous electrical conductivity in the food to be treated is important.Product focus Very suitable for products with large particles or products that may cause severe fouling.Cos
36、t index Very dependent on electricity price and running time.When comparing equal running times,TCO is 5-20%higher for ohmic than conventional heat exchangers(the version we compared with was a Tetra Pak coiled heat exchanger).Commercialization Fully commercialized with+100 installations Opportunity
37、 Treatment of high-fouling products or products with large particles,with high particle concentration.Potentially fewer organoleptic changes than for conventional indirect heat treatment due to the rapid heating and absence of hot surfaces.History The concept of ohmic heating of foods is not new.In
38、the nineteenth century,several processes that used electrical current for heating flowable materials were patented.In the early twentieth century,“electric”pasteurization of milk was achieved by passing milk between parallel plates with a voltage difference between them,and six states in the USA had
39、 commercial electrical pasteurizers in operation.The technology disappeared in succeeding years,apparently due to the lack of suitable inert electrode materials and controls.Improved materials and designs for ohmic heating are now available.Operating principle Ohmic heating is defined as a process w
40、herein an electric current(usually alternating)is passed through foods or other materials with the primary purpose of heating them.The heating occurs in the form of internal energy generation within the material and is very quick.Ohmic heating is distinguished from other electrical heating methods b
41、y the presence of electrodes in contact with the food,and by the frequency and waveform.There are different arrangements of the electrodes:9 General parallel plate,parallel rod,collinear and staggered rod,that can be used depending on application(Sakr&Liu,2014).The electrode material can be titanium
42、,stainless steel,platinized titanium,aluminium and graphite.The electrical conductivity of the food should preferably be in the range 0.01-10 S/m.The conductivity of food stuff can,if necessary,be altered by soaking in salt solutions or by leaching.Microbiological effect There is no data found on an
43、y organism with an unusual resistance to ohmic heating.There are reports on an additional non-thermal lethal effect of ohmic heating due to the electrical current causing electroporation of the microbial cells.Since ohmic heating is fundamentally a thermal-based process,temperature and time are the
44、principal critical process factors and it is important to identify the coldest zone in the food matrix.The acidity,composition,total solid content and viscosity of the liquid food can affect the heating up rate.Studies have shown that particle concentration can affect the heating up time of the part
45、icles,showing the significance of particle resistance to the overall circuit resistance.Chemical effect Ascorbic acid degradation in orange juice during electrical and conventional heating was studied to determine if the presence of an electric field altered the rate of degradation.Analysis showed t
46、hat electric field has no significant effect on ascorbic acid degradation.Effects of electrolysis on ascorbic acid occurred with stainless steel electrodes,but were not evident with specially coated titanium electrodes.These phenomena did not affect ascorbic acid concentration.A study on fruit desse
47、rts showed no difference in degradation of ascorbic acid compared to conventional heating(Louarme and Billaud,2012).Mercali et al.(2014)studied the degradation of ascorbic acid and colour changes in acerola pulp and concluded that at frequencies above 100 Hz ohmic and conventional heating gave simil
48、ar results.However,it is not only the frequency itself that can cause degradation;the current density/frequency ratio is also important.Investigations by Pataro et al.(2014)show that the number of ions released from stainless steel electrodes into the food depends on the frequency,and on the conduct
49、ivity and pH of the food.At the lower frequencies of 50-60 Hz used in the beginning of the ohmic era,erosion of electrodes was a large problem.Today a frequency of at least 15 kHz is used,and this in combination with better materials in the electrodes has reduced the erosion problem to a minimum(DR0
50、030336).With the right process design,the AISI 316 material is very suitable for electrodes.10 General Suitable products Very suitable for products with large particles or sensitive to fouling products,such as Liquid egg Processed cheese Vegetables Fruit products with pieces(whole fruits,sliced frui
51、ts)Fruit preparations(jams,compotes,marmalades,etc.)Fruit concentrates Fruit juices Soups and sauces Tomato products Advantages Simultaneous heating of particles and liquid For large particles,the simultaneous heating of particles and liquid shortens the retention time and minimizes system volume,gi
52、ving a better product quality;this advantage increases with the size of particles.Less fouling during heating For products that are very sensitive to fouling,such as egg,the cold pipe surfaces are an advantage and can improve running time.Disadvantages Demands in power supply An ohmic heating instal
53、lation often requires expansion of the power supply into the factory due to high electricity consumption.Capacity limits The maximum capacity in an ohmic line is limited by the installed power supply.Homogenous electric conductivity is important The process parameters of ohmic heating are dependent
54、on food characteristics and this determines the rate of heating.If the electrical conductivity difference between particles and liquid is significant,particle pre-treatment might be necessary to avoid uneven heating.Summary Ohmic heating is based on heat with time and temperature as control paramete
55、rs,and heat is transferred into the food by current.The main advantages for ohmic heating are that the method is rapid and instant.However,heating is dependent on the food characteristics and sometimes needs a well-controlled pre-treatment.More research is needed to understand the formation of cold
56、spots and overheating of multiphase foods.11 General MICROWAVE Other names Dielectric heating Process Uses electromagnetic waves of certain frequencies to generate heat in the food.Effect Microbial inactivation with microwave energy follow the same kinetics as conventional thermal methods.Advantages
57、 Simultaneous,rapid,heating of liquid and particles(volumetric heating).Low fouling since no hot surfaces.Disadvantages High demand on electric power supply causing capacity limits,high investment cost.Product focus Solid food(e.g.bake off,ready meal)and particulates.Cost index very dependent on ele
58、ctricity price and running time.When comparing equal running times,investment cost about 1.5 times higher and TCO 10-25%higher than conventional heat exchangers(the version we compared with was a Tetra Pak coiled heat exchanger).Commercialization Commercialized for packed food.Liquid,unpacked food i
59、n the beginning of commercialization.Opportunity Treatment of high-fouling products or products with large particles with high particle concentration.Potentially fewer organoleptic changes than for conventional indirect heat treatment due to the rapid heating and absence of hot surfaces.Biggest chal
60、lenge is to control the coldest spot and to reach uniform heating,which is influenced by many factors,such as product formulation and equipment design.History The development of the cavity magnetron by two British physicists during World War II led to the discovery of microwave heating.Individuals w
61、orking at Raytheon radar laboratory on microwave waveguides observed the popping of corn kernels near the radiation tubes.The development of microwave heating is attributed to Percy Spencer at Raytheon,who filed a US patent in 1945.Microwave heating or dielectric heating is used in industry for many
62、 different applications;one early example is from 1940,when a company developed a technique for quick hardening of the bonding cement used in the production of plywood.Sixty years later,the number of microwave processing units in the food industry was estimated at one thousand worldwide(Raaholt 2015
63、).Operating principle Microwaves are electromagnetic radiations,which are synchronized oscillations of electric and magnetic fields,perpendicular to each other within the frequency range of 300 MHz to 300 GHz(time interval between the wave peaks is 3x10-8 to 3x10-11 seconds)(Cullen et al.2012).Figur
64、e 1 illustrates these properties.12 General The common frequencies used in industrial microwave heating are 915 MHz and 2450 MHz,with 915 MHz being the dominating frequency in North America and UK and 2450 MHz in the rest of Europe in(Raaholt 2015).Figure 1.Electromagnetic wave components Heating of
65、 the material subjected to microwaves occurs due to interaction of the electric field of the microwave with charged particles and molecules in the material.The charged particles will move(if free)and travel with the field(after a lag),creating a current that is termed as ionic polarization or ionic
66、conduction.Water molecules are dipolar and will reorient themselves with the changing electric field(Hebbar et al.2012).This is called dipole polarization or orientation polarization.The electric field can also give rise to a dipole moment in nonpolar molecules,due to induced dipoles.The movement of
67、 charged particles and molecules increases the temperature,which also gives rise to convective or conductive heat in the neighbouring food components(Raaholt,2015).Water is probably the most important ingredient in any microwavable food.Usually the higher the water content,the better the heating.The
68、 dielectric properties of the product will also influence the heating.Microbiological effect The critical process parameters of microwave processing are time,temperature and location of the coldest point,which is affected by many factors,particularly equipment design and product formulation.13 Gener
69、al Since the beginning of microwave processing,there has been controversy about the possible non-thermal effects of microwave processing.As many as four separate effects have been proposed(Chandrasekaran et al.2013):Selective heating of microorganisms solid microorganisms are heated more effectively
70、 by microwaves than the surrounding medium and thus are killed more readily.Electroporation caused when pores form in the membrane of the microorganisms due to electrical potential across the membrane,resulting in leakage.Cell membrane rupture related,in that the voltage drop across the membrane cau
71、ses it to rupture.Cell lysis occurs due to coupling of electromagnetic energy with critical molecules within the cells,disrupting internal components of the cells.The consensus is that the reported non-thermal effects are likely to be due to the lack of precise measurements of the time-temperature h
72、istory and its spatial variations.No solid proof exists that microwaves have an extra killing effect,and we conclude that microwaves only have a thermal killing effect.Chemical effect As well as microbial inactivation,enzyme inactivation by microwave energy in general has been explained as the resul
73、t of thermal effects.Advantages Simultaneous heating of particles and liquid For large particles,the simultaneous heating of particles and liquid shortens the retention time and minimizes system volume,giving a better product quality;this advantage increases with the size of particles.Less fouling d
74、uring heating Few hot surfaces;for products that are very sensitive to fouling,such as egg and high-TS quark-type cheeses,the cold pipe surfaces are an advantage and can improve running time.High particle concentrations Can handle products with particle concentrations above 70%.Smaller footprints Le
75、ss fouling and rapid heating lead to smaller equipment being necessary.14 General Disadvantages High investment cost As an example,the investment cost for a 1,500 l/h microwave solution with temperature program 60-136-25C is likely to be 40-45%higher than a coiled heat exchanger(DR0031032).May requi
76、re rebuilding and investment in power supply Depending on required electrical energy,microwave heating installation might require expansion of the power supply into the factory due to high electricity consumption.Capacity limitation Upper limit around 5,000 l/h,due to power requirement.Measuring die
77、lectric properties is not enough to determine how microwave energy converts to heat.Summary Microwave heating is an electrothermal process where inactivation is based on heat with time and temperature as control parameters.The microwave processing of food products is often used with pre-packaged foo
78、d.The biggest challenge is to control the coldest spot and to reach uniform heating,which is influenced by many factors,such as product formulation and equipment design.Microwave heating could be seen as an opportunity for treatment of high-fouling products or products with large particles.15 Genera
79、l RADIO FREQUENCY HEATING Other names dielectric heating,RF heating Process uses electromagnetic waves of certain frequencies to generate heat within food matrices.The penetration depth is larger than that for microwaves,due to the shorter wavelengths used.Effect The microbial inactivation is based
80、on a thermal effect.The experimental studies performed so far show very minor effects on product quality Advantages Simultaneous,rapid heating of liquid and particles(volumetric heating).Deeper penetration compared to microwaves.Disadvantages High demand on electric power supply Product focus Cost i
81、ndex Not investigated Commercialization Very limited in continuous pasteurization of food.Commercialized for drying,baking and thawing of frozen meat and in meat processing.Opportunity More research is needed on industrial applications.History The existence of electromagnetic fields was postulated i
82、n 1832 by Michael Faraday.Sherman(1946)described“electric heat”with a possible application in food processing.The early developments of RF were in the area of cooking of processed meat,heating of bread,dehydration and blanching of vegetables.None of these were commercialized mainly due to the high o
83、verall operating cost at that stage.The first commercial applications focused on defrosting frozen products.The next generation of commercial applications was post-bake drying of cookies and snacks in the late 1980s.In the late 1990s RF pasteurization was studied to improve energy efficiency and sol
84、ve the problems with runaway heating,in which certain areas are heated much faster than others due to their higher ability to absorb energy,creating a large difference in temperatures.That led to recent investigations of RF applicator modifications and dielectric properties of food at RF frequencies
85、.Operating principle Radio frequency heating uses the electromagnetic field in the range of 1-300 MHz.The frequencies used for industrial,scientific and medical applications are 13.56,27.12 and 40.68 MHz,respectively.When an alternating electrical field is applied to a food,one phenomenon that occur
86、s is the movement of positive ions in the material towards the negative regions of the electric field and the movement of the negative ions towards positive regions in the field.This is often referred to as ionic depolarization and is essentially resistance heating as in ohmic heating.Heating occurs
87、 because this field is not 16 General static,with polarity continually changing at high frequencies(27.12 MHz for RF and 915 or 2450 MHz for microwave).Regardless of the frequency,the reversal of polarity leads to oscillation of ions forwards and backwards in the product,with friction generating int
88、ernal heat.In addition,dipolar molecules like water will also try to align themselves with the changing polarity(dipole rotation),and this movement also cause friction that can lead to heat generation.Both microwave and radio frequency heating are classified as dielectric heating methods.The ionic d
89、epolarization is the dominant heating mechanism at the lower frequencies in the RF range,while both ionic depolarization and dipole rotation are relevant in microwave heating,depending on the moisture and salt content of the product.For RF,dissolved ions are more important for heat generation than t
90、he water dipoles in which they are dissolved.In an RF heater the food is placed between the applicator electrodes,where complex electrical impedance is introduced into the RF electrical field.Microbiological effect RF is comparable to microwave heating,with microbial inactivation based on a thermal
91、effect.Experimental studies on microbial inactivation by RF heating showed a reduction of E.coli K12 from 3-4.8-log cycles in apple juice,orange juice and apple cider.RF equipment has been validated for sterilization of mashed potatoes and scrambled eggs inoculated with C.sporogenes.Chemical effect
92、Experimental studies performed so far show very minor effects on product quality.Suitable products Meat processing Foods containing particulates High-viscous foods In-shell eggs Disinfection of agricultural commodities Post-baking drying of cookies and crackers Blanching of vegetables.Research and d
93、evelopment Fraunhofer Institute has conducted laboratory and pilot-plant studies of continuous-flow radio frequency heating of highly viscous foods and foods with large particles.17 General Advantages RF is a rapid heating method and some claim it has advantages over conventional heating methods,par
94、ticularly considering product quality.It heats more uniformly compared to microwave,due to both deeper penetration and simpler field patterns.Although pathogens in low-moisture foods are much more difficult to inactivate than in high-moisture foods,RF heating has a potential to address emerging food
95、 safety concerns associated with high and low-moisture foods(Jiao et al.2018).Disadvantages Radio frequency heating has not been fully commercialized due to lack of available data on microbial inactivation,product quality and shelf life.The primary barrier is still the nonuniformity of heating(Jiao
96、et al.2018).Energy costs can be large and an optimized scale-up is needed.More efforts are needed before industry will take on radio frequency heating on a larger scale.Summary Radio frequency heating is a volumetric heating method as is microwave processing,but it has a deeper penetration and more
97、uniform field pattern.It is based on a thermal inactivation of microbes.Radio frequency has not been fully commercialized due to lack of available data on microbial inactivation,product quality and shelf life.More systematic research is needed on industrial applications.18 General HIGH-PRESSURE PROC
98、ESSING Other names Ultra High-Pressure processing(UHP),High-Hydrostatic Pressure processing(HHP)Process Semi-continuous or batch process where pressures at 300-1000 MPa are used to inactivate microorganisms.Effect Destroys vegetative bacteria,yeasts,moulds and viruses at low temperatures but has lim
99、ited effect against bacterial spores unless combined with other treatments,such as heat.Advantages Can be used for heat-sensitive products.Does not distort particulates.May deactivate some enzymes.Products perceived as fresh Disadvantages Only a pasteurization process.High investment and running cos
100、ts.Enzymes not fully deactivated.Product focus Looking on the technology on its own,not combining it with high temperature,it is suitable for high-quality high-acid and refrigerated low-acid products.Cost index Production cost about 10 times more expensive than traditional heat treatment.Capital cos
101、t estimated to be close to 40 times higher.Commercialization Pre-packed food such as juices,smoothies,fruit pures,meat,seafood,guacamole,etc.Several hundred commercial installations around the world(Drinktec 2017).Opportunity Good complement to heat treatment within food and beverage HPP is approved
102、 by the FDA for use on foods.HPP is a semi-continuous or batch process where pressures at 300-1000 MPa are used to inactivate microorganisms.It is mainly a pasteurization process and to obtain sterilization a combination of high pressure and elevated temperatures in the range of 60-110C are needed.T
103、he target organisms for the process need to be well chosen.There has been a steady growth in the HPP market since 2003 and it is still growing at a steady pace.Global food production using HPP was,according to DIL,350 million kg in 2012.Meat and vegetable products accounted for about half of this an
104、d juices and beverages for about 14%(Toepfl 2014).Hiperbaric,a supplier of HPP equipment,estimated the global HPP production of juices and smoothies to 330 million kg.That corresponds to a value of over 3 billion euro for HPP beverages in stores in 2016.The expected growth rate is 20-25%per year unt
105、il 2025(Hiperbaric 2017).History The fact that high pressure can kill bacteria and modify the texture of some foods has been known since 1899,when it was demonstrated that it could be used to preserve milk(Hite 1899).The technology started to be used for production of industrial diamonds,ceramics,an
106、d fuses during the 1970s.The food industry could 19 General not make use of this technology until pressure vessels suitable for food use became available in the late 1980s.Operating principle High-pressure processing of foods uses different types of industrial equipment.Typically,it requires a press
107、ure vessel of 50-550 litres capacity and a pressure-generating device.Food packages are loaded into the vessel and it is closed.Water is used as pressure transmitting fluid and is pumped into the vessel.The process is isostatic,so pressure is transmitted rapidly and uniformly throughout both the pre
108、ssure transmitting fluid and the food with little or no heating.The work of compression during HPP treatment increases the temperature of foods through adiabatic heating,approximately 3C/100MPa,depending on the composition of the food.The pressure is equal from all sides,so the product shape is not
109、distorted.A normal cycle time is 8-10 minutes,of which the target pressure hold times can be 3-6 min.Once the target pressure is reached,the pumping is stopped,valves are closed,and the pressure can be maintained without further energy input.A semi-continuous system,where the liquid food may be plac
110、ed directly in a pressure vessel and aseptically packed after pressure treatment is under development(Hiperbaric 2017).Microbiological effect HPP is well suited for destroying vegetative bacteria,yeasts,moulds and viruses at low temperatures,but has limited effect against bacterial spores unless com
111、bined with other treatments,such as heat.Vegetative cells need pressures above 300 MPa(3,000 bar)to be inactivated at ambient temperature,while spores can survive pressures above 1,000 MPa.HPP Pasteurization gives a prolonged shelf life under refrigerated conditions.Sterilization with HPP requires o
112、perating temperatures above 90C in combination with very high pressure,up to 900 MPa,in order to inactivate spores.This is often referred to as pressure-assisted thermal sterilization(PATS).High pressure triggers spore germination and thus pulsed or oscillating pressurization in combination with hea
113、t is more effective in spore inactivation than continuous pressure.Microorganisms vary in their sensitivity to high pressure and generally gram-negative bacteria are more sensitive to HPP than gram-positive bacteria.Studies have shown that bacterial cells are most resistant at neutral pH and that th
114、e resistance can vary between strains(Patterson et al.1995).HPP treatment of 5-15 min at 350-600 MPa results in what could be called“cold pasteurization”of most foods.E.coli O157:H7 and Salmonella spp.are key concerns in the development of effective HPP food treatments.Spores are much more pressure-
115、resistant than vegetative microorganisms,with C.botulinum being the most pressure-resistant spore known.20 General The mechanism of HPP inactivation is understood to be a combination of effects on cell walls and protein structures.Numerous studies have shown loss of intracellular constituents from m
116、icroorganisms after pressure treatment,and electron microscopy pictures have shown damage to the microorganism morphology.Leakage of intracellular components from the cells indicates damage to the cellular membrane,and the greater the amount lost from cells,the greater degree of death and injury.Com
117、pression appears to affect microbial inactivation by altering the proteins responsible for replication,integrity,and metabolism.High pressure will not affect covalent bonds but will alter hydrogen and ionic bonds responsible for maintaining proteins in their biologically active form.Thus,observed mi
118、crobial inactivation kinetics can be postulated to be the result of the irreversible denaturation of one or more critical proteins in the microbe.Chemical effect Sensory and textural quality changes of products with a certain protein content may occur due to protein denaturation.The starch component
119、 of products may cause the product to swell when exposed to HPP.The effect of HPP treatment on enzyme activity varies with different enzymes.Some enzymes are reversibly inactivated at 100-400 MPa.Enzymes generally require higher pressure for inactivation.In general,thermal treatment is more effectiv
120、e than HPP treatment for irreversible enzyme inactivation but a combination of pressure and moderate temperature can produce enzyme inactivation at low temperature.However,HPP alone may also cause activation or enhancement of enzyme activity.Trials on orange juice comparing HPP and thermal treatment
121、(DR0031050)showed that:HPP inactivates PME enzymes in orange juice to the same extent as the heat treatments 72C/15 s and 80C/15 s.(Industry standard for PME inactivation is 95C/15 s).Colour changes due to processing were very small in both HPP and heat treatments.No difference in Vitamin C degradat
122、ion between HPP and heat treatments.It is primarily the amount of dissolved oxygen in the product that determines Vitamin C retention(Tetra Pak 2016).Sensory evaluation of orange juice showed significant difference between HPP and 80C/15 s but not vs.72C/15 s.Packaging requirements Here are some tip
123、s for HPP-ready package design straight from Dr.Errol Raghubeer,Avures Senior Vice President,HPP Science and Technology(Avure 2014):Use flexible packages that can conform to the product under pressure and wont experience permanent deformation.Wider seals will help the package withstand high pressure
124、.If semi-rigid packages are used,make sure they can recover 21 General their shape after headspace compression.Do not use material that breaks before distortion,such as glass,or cannot recover from distortion,such as metal Minimizing headspace reduces the potential for permanent deformation or catas
125、trophic failure.Blow-moulded bottles with simple sidewall designs combined with rigid bottoms and top shoulders are effective.Cylindrical or rounded corner sidewall cross-sections are preferred,providing large symmetrical areas to accommodate volume reduction.Lid films should be thick enough and str
126、ong enough to withstand the tensile forces imposed during HPP,and lidding seals are typically wider than normal.Cost Heinz and Toepfl(2016)from DIL,the German Institute for Food Technology,estimated typical processing costs for heat treatment(HTST)and High-Pressure Processing(HPP)(see Table 1).They
127、found that the processing cost for HPP is 30-40 times as expensive as HTST,based on a capacity of 2,000-3,000 l/h.Table 1.Typical processing costs of HTST vs HPP(Heinz and Toepfl 2016)HTST HPP Typical processing costs 0.005-0.01/l 0.20-0.30/l Sampedro et al.(2013,2014)analysed costs based on process
128、ing conditions that met the US FDA requirements of a 5-log reduction of pathogenic microorganism.They calculated the total production cost for producing 16,500,000 l/year(3,000 l/h)of orange juice(see Table 2).The HPP production cost was 7 times higher than that of the thermal treatment(heat recover
129、y of 96%was used for the thermal treatment).The capital cost of HPP was estimated to be close to 40 times higher than that of thermal treatment and.Table 2.Production costs of orange juice(Sampredo et al.2013,2014)Orange juice pasteurization 16,500,000 l/year Thermal 87.5C/5 sec HPP 500 MPa/90 sec C
130、apital cost($/l)0.0008 0.031 Production cost($/l)0.015 0.107 Aganovic et al.(2017)made an energy balance and life cycle assessment(LCA)comparing conventional thermal(74C/30 sec)and HPP(600 MPa/5 min)on tomato juice and watermelon juice.For the thermal treatment 70%heat recovery 22 General was assume
131、d.Their results showed that HPP required almost five times more energy than thermal treatment.From an LCA perspective there was no huge difference.The largest environmental impact was associated with the production of 250 ml PET bottles.Advantages High-pressure processing can be applied at room temp
132、erature,a benefit for treating heat-sensitive products The process is isostatic(uniform throughout the food),i.e.it does not distort particulates.The process may deactivate some enzymes.High-pressure processing does not break covalent bonds,therefore,development of flavours alien to the product is p
133、revented maintaining the natural qualities of the products.Textural changes may lead to the development of novel foodstuffs.Disadvantages Bacterial spores are very resistant to pressure and require very high pressure(1,000 MPa)combined with heat for their inactivation.High capital and running costs
134、Summary HPP is a commercialized process used for pasteurization at ambient temperatures,which makes it suitable for heat-sensitive products.Sterilization of food requires a combination of high pressure and high temperature,around 100C.All enzymes are not readily inactivated,which in some cases can b
135、e a benefit.There is no difference in vitamin C degradation or colour degradation between HPP and heat treatments of orange juice.Capital costs are very high compared to thermal treatment equipment.This in combination with higher energy demand leads to a production cost significantly higher than for
136、 heat treatment.23 General ULTRA HIGH-PRESSURE HOMOGENIZATION Other names dynamic high pressure Process Homogenization at pressures in the range 200-400 MPa.The temperature increases 20C/100 MPa.Treatment temperature depends on inlet temperature.Effect We have found no data proving that the killing
137、of bacterial spores is better with UHPH than thermal treatment at the same temperature and time as the UHPH.Advantages Continuous process.Can change physical properties such as viscosity and particle size.Disadvantages Maximum particle size 100 m.Can change physical properties such as viscosity and
138、particle size.Product focus Smooth products without particles.Cost index Estimated to be 3-7 times more expensive in investment and require 2-6 times more energy(in kW),depending if compared to an indirect or direct heating system.Commercialization Not for pasteurization.Opportunity Operating princi
139、ple Comparing dynamic high-pressure processing with static high-pressure processing,the big difference is that in static processing the pressure is uniformly transmitted throughout the sample(in its package)by the pressure-transmitting media(usually water in food applications);while in dynamic proce
140、ssing the liquid is forced through a homogenization valve.During UHPH processing the temperature of the product will increase by 17-21C per 100 MPa(Dumay et al.2013)compared to its inlet temperature.The holding time at the elevated temperature in the high-pressure valve is short,about 0.1 0.7 second
141、s.Microbiological effect The effect of UHPH on indigenous microbiota in apple juice has been studied(Surez-Jacobo 2010),finding reductions of 3.6-5.9-log units on populations of aerobic mesophilic count,psychrotrophic bacteria,lactobacilli,Enterobacteriaceae,faecal coliforms,moulds and yeasts.The in
142、activation effect is thought to be a combination of the pressure and the temperature.The log reduction became higher as the pressure increased from 100 MPa to 300 MPa,but at the same time the temperature in the homogenization valve also increased from around 40C to 90C.Velzques-Estrada et al.(2011)i
143、noculated Listeria monocytogenes and Salmonella enterica serovar Senftenberg 775W in orange juice and grape juice,to a level of 7-log cfu/ml to evaluate inactivation at pressures of 200,300 and 400 MPa.The temperatures achieved during the treatments were 51.3C,62.4C 24 General and 74.2C respectively
144、 and the holding time estimated at less than 0.7 s.Listeria monocytogenes was the more resistant of the two microorganisms,showing a log reduction of about 2 at 200 MPa and about 5 at 300 MPa and 400 MPa.Salmonella enterica serovar Senftenberg 775W showed log reductions of about 2 at 200 MPa,5 at 30
145、0 MPa and 6.5 at 400 MPa.The theoretical log reductions of Listeria monocytogenes at heat treatment of 75C/1 second in milk would be 0.7 if D72=4.2 seconds and z=6.5C are used,but if D65=6 seconds and z=6.6C are used,the log reduction is 5.5.Roig-Sagus et al.(2015)inoculated orange juice with spores
146、 of Alicyclobacillus acidoterrestris(CECT 7094)and Alicyclobacillus hesperidium(CECT 5324)from the Spanish Type Culture Collection(CECT).The inoculated juice was UHPH-treated at 300 MPa at inlet temperatures from 20C to 80C,resulting in peak temperatures at the homogenization valve of 93C-130C.The l
147、og reduction increased with increasing temperature and gave a complete inactivation(around 5-log)at the highest temperature.However,they also theoretically calculated the contribution of the temperature alone and came to the conclusion that no synergistic effect could be determined between the press
148、ure and temperature at the treatment conditions used.All measured reduction was due to temperature.In soymilk treated at 200 MPa and 300 MPa log reductions of total count of 2.42 and 4.24 were detected,respectively,while the reduction of spores was around 2-log(Cruz et al.2007).The inlet temperature
149、 of the soymilk was 40C,which means that the temperature at the homogenization valve was around 80C at 200 MPa and 100C at 300 MPa.Georget et al.(2014)evaluated the reduction of spores of Geobacillus stearothermophilus ATCC7953 and Bacillus subtilis PS832 in PBS buffer 0.01 M and concluded that the
150、temperature appears to be the main contributor to spore inactivation by UHPH.They could see no significant germination of spores induced by the UHPH treatment.Others have found germination of spores by high pressure but then the residence time at the high pressure was much longer,so the authors beli
151、eve that the exposure time is important in triggering the germination.Espejo et al.(2014)inoculated milk with spores of B.cereus,B.licheniformis,B.sporothermodurans,B.coagulans,G.stearothermophilus and B.subtilis and evaluated the log reduction at 300 MPa at different inlet temperatures of the milk.
152、They found that the log reduction achieved depended on the inlet temperature.The inlet temperatures used were,55,65,75 and 85C resulting in homogenization valve temperatures of around 113,121,130 and 140C,respectively.At an inlet temperature of 75-85C a log reduction of around 6 was achieved for B.c
153、ereus,B.licheniformis,B.sporothermodurans and B.coagulans,while it was a bit lower for G.stearothermophilus and B.subtilis,at 4.5-5-log.The residence time at the high pressure was estimated to be less than 0.5 seconds.A comparison of the log reductions achieved when treating an almond beverage with
154、UHPH and traditional heat was made by Valencia-Flores et al.(2013).The residence time at the high pressure(and temperature)was estimated to be less than 0.7 seconds.Incubation at 30C for 20 days showed that only the UHT-treated 25 General samples and the samples treated at 300 MPa with 65C to 75C in
155、let temperatures were sterile.The detection limit was-0.5-log cfu/ml.The theoretical reduction of Bacillus cereus spores due to the heat during the high-pressure treatment can be calculated.The log reduction depends on the D-and z-values used and different values for Bacillus cereus can be found in
156、the literature.At a temperature treatment of 124C/0.5 seconds,which could be compared to the 300 MPa treatments,D123=177.6 seconds and z-value 7.9C(Mazas et al.1999)gives no log reduction.If D100=18.6 seconds and z-value 8C(Mazas et al.1999)is used,the log reduction becomes 26.9 instead.Thus it is n
157、ot possible,based on these findings,to draw any conclusions that the pressure contributes to the reduction of Bacillus cereus spores.Chemical effect Ascorbic acid Comparing the degradation of L-ascorbic acid(L-AA)during thermal pasteurization with that during UHPH,Velzques-Estrada et al.(2011)found
158、that pasteurization at 90C/1 min gave a reduction of 17.4%,but also reported finding reductions of 8%in the literature,under the same conditions.UHPH treatments at 100,200 and 300 MPa showed decreases of 2%,5%and 11%,respectively.However,the highest temperatures achieved at the different pressures w
159、ere different:45C,70C and 94C for the 100,200 and 300 MPa,respectively.The residence time at the maximum temperature was estimated to be 0.7 s or less.When evaluating the influence of UHPH on bioactive compounds in apple juice,Surez-Jacobo et al.(2011)came to the conclusion that there was no effect
160、on the total phenolic content and no effect on the ascorbic acid and dehydroascorbic acid activity,when the apple juice was treated at 100,200 and 300 MPa,inlet temperature 4C and 20C.PME(pectin methylesterase)Velzques-Estrada et al.(2011)observed a reduction of more than 96%in the PME activity in o
161、range juice after a single pass at 200-300 MPa.The temperatures at these pressures were between 68-95C,depending on the inlet temperature and pressure used.In traditional heat treatment the first pasteurization of juice is made at 95-98C/10-30 seconds to inactivate enzymes.Total polyphenols Velzques
162、-Estrada et al.(2011)did not observe any significant difference in total polyphenols between fresh and UHPH-treated orange juice.They did find a significant difference between the fresh juice and the juice pasteurized at 90C/1min.26 General Fat globules UHPH gives a greater reduction in fat globule
163、size than conventional homogenization+pasteurization.The adsorption of non-native MFGM(milk fat globule membranes)differed compared to conventional homogenization,where mainly intact casein micelles were adsorbed.In the UHPH-treated milk,the casein micelles were disrupted,and casein molecules were d
164、irectly bonded to the MFGM material.Whey proteins were,in addition to direct interaction with native MFGM proteins,also adsorbed through disulphide bonding with both indirectly and directly adsorbed casein molecules(Zamora et al.2012).Protein denaturation DSC(differential scanning calorimetry)was us
165、ed to evaluate the amount of denatured 11S globulin in soymilk(Cruz et al.2007).UHT(142C/2 s)and 300 MPa(input 40C;valve temperature 100C)treated samples showed no endothermic peaks for 11S protein,indicating a total denaturation.Proteolysis The degree of proteolysis in yoghurts made from milk treat
166、ed with UHPH at 200 or 300 MPa and at 30C or 40C inlet temperatures were compared with those produced from milk treated at 90C/90 seconds,homogenized in one stage at 15 MPa and fortified with 3%skim milk powder(Serra et al.2009).The conclusions were that the proteolysis was very similar between the
167、treatments.Greater concentrations of hydrophobic peptides were found in the 200 MPa yoghurts.These peptides could result in an undesirable bitter taste.Particle size The particle size in soymilk base product,BP,(extracted and homogenized in a two-step homogenizer),UHT soymilk(the BP treated at 142C/
168、2s)and UHPH-treated soymilk were compared.The UHPH soymilk exhibited a considerable reduction in particle size compared to UHT and BP(Cruz et al.2007).Comparing UHT-treated milk(138C/4s),homogenized in two steps(18MPa+4MPa)with milk UHPH-treated at 200 MPa or 300 MPa,the particle size distribution w
169、as changed from bimodal to monomodal by processing at 200 MPa(Amador-Espejo et al.2014).Processing at 300 MPa showed no change in the bimodal distribution.At processing at 300 MPa and an inlet temperature of 85C,formation of larger particles was observed.This is explained by the formation of fat agg
170、regates due to limitation in the amount of available casein to cover the surfaces of the smaller fat globules created.Gel firmness Yoghurts from milk UHPH-treated at 200 or 300 MPa had a greater gel firmness,less syneresis and lower titratable acidity than those obtained from conventionally treated
171、milk fortified with skim milk powder(Serra et al.2009).27 General Cost No homogenization included in traditional process UHPH is estimated to be 3-7 times more expensive in investment cost than traditional heat treatment and requires around 2-6 times more energy(in kW)depending on if it is compared
172、to an indirect or direct system(DR0029779).Homogenization included in traditional process.UHPH is estimated to be 2.5-4 times more expensive in investment cost than traditional heat treatment including homogenization,and requires around 1.4-3.4 times more energy(in kW)depending on if it is compared
173、to an indirect or direct system(DR0029779).Advantages The advantage of the UHPH process over traditional static high-pressure processing,HPP,is that it is a continuous process.Disadvantages There is a limit in particle size of 100 m.UHPH treatment can denature caseins and this can lead to organolept
174、ic changes in the product.The UHPH can change physical properties,such as viscosity and particle size of the treated products and this can have an effect on the final product quality,both desirable and undesirable.Summary We have found no data proving that the killing of bacterial spores is better w
175、ith UHPH than thermal treatment at the same temperature and time as is reached during the UHPH.28 General ULTRAVIOLET LIGHT Other names UV,UVC Process The product is irradiated by UVC light.Effect UVC light(200-280 nm)induces mutations in the DNA of the microorganism.The critical parameter is UVC do
176、se.Advantages Low capital and maintenance cost.Disadvantages Can accelerate development of rancid taste in products containing free fatty acids.Process must be optimized for every product,since it depends on the UVC transmission.Product focus Clear liquids without fibres or pulp.Cost index Depends o
177、n the product and target microorganisms,but in general lower than conventional heat treatment.Commercialization Widely used on water.To some extent on clear fruit juices.Opportunity May be useful wherever water or clear juices are blended with other components.History UV light has been used for disi
178、nfecting drinking water and wastewater systems for many years but there has been limited research on food products.Studies have been conducted on apple juice,apple cider,wine and milk.Operating principle UV processing uses radiation from the ultraviolet region of the electromagnetic spectrum for dis
179、infection,usually in the range of 100-400 nm wavelength for food applications.This range may be further subdivided into UVA(315 to 400nm),normally responsible for changes in human skin that lead to tanning;UVB(280 to 315 nm),which can cause skin burning and eventually lead to skin cancer;UVC(200-280
180、 nm),called the germicidal range since it effectively inactivates bacteria and viruses;and the vacuum UV range(100 to 200 nm),which can be absorbed by almost all substances and thus can be transmitted only in a vacuum.The parameter determining the effective disinfection is the UV dose.The UV dose is
181、 the intensity of the UV light multiplied by the time of the exposure.UV dose is given in J/m2 or mJ/cm2(1 mJ/cm2=10 J/m2).For liquid products in continuous systems the dose is sometimes given as J/L(total UV C output per unit(W)/Flow rate(L/s).To translate J/L to J/m2 the configuration of the react
182、or and the flow rate must be known.To get the right intensity of the UV lamp to provide the needed dose,the UV absorption(UV transmission)of the medium must be known.The UV absorption is dependent on the colour and amount of organic matter in the medium(food).29 General For food with high UV absorpt
183、ion,for example milk,it is difficult to provide the UV dose needed for proper disinfection even if treated in a very thin film.Optimization of the UV treatment is required for every new food product to be able to determine the correct UV dosage.Further studies are needed regarding UV dosage and infl
184、uence on colour,sensory and nutritional quality.UV light can be used as a continuous light or as pulsed UV light.Pulsed light has a higher penetration depth and may be more effective than continuous UV light.Scaling of the lamps might influence the efficiency of the UV lamps during their lifetime.UV
185、 lamps are also made of glass and it is unsuitable to use glass in direct contact with food.Microbiological effect The germicidal properties of UV irradiation are mainly due to DNA mutations induced through absorption of UV light at 254 nm by DNA molecules.This mechanism of inactivation results in a
186、 sigmoid curve of microbial population reduction.The end of the curve has a tailing phase due to UV resistance of the microorganisms and to experimental artefacts,such as suspended solids that may block the UV irradiation.UV light at 222 nm(Far UV)and 282(Far UV+)nm have also been used to inactivate
187、 microorganisms.The choice of wavelength is dependent on the target microorganism and the medium where the inactivation takes place.To inactivate Escherichia coli O157:H7 in apple juice,222 nm was more effective than 254 nm(Yin et al.2014).The colour of the microorganisms can influence the UV dose n
188、eeded for inactivation.For example,Aspergillus niger spores,which are black,need a much higher dose for inactivation than mutants of the same species that are cream-coloured(Esbelin et al.2013).UV has been used for years for water sterilization,showing effectiveness against a wide variety of microor
189、ganisms.For disinfection of water,it is essential that all parts of the product receive an UV radiant exposure of at least 400 J/m2 (at 254 nm)to reduce human pathogens and viruses by at least 4-log cycles.Critical factors for the effect of UV light include the transmissivity of the product,the geom
190、etric configuration of the reactor,the power,wavelength and physical arrangement of the UV source,the product flow profile and the radiation path length.UV may be used in combination with other process technologies,including powerful oxidizing agents,such as ozone and hydrogen peroxide.UV light has
191、also been used successfully on beef,fish and poultry to control bacteria and increase shelf life while causing little effect on food quality.Some studies show a 5-log reduction of pathogens in clear juices.This meets the FDA requirements of 5-log reductions on most pertinent pathogenic organism in f
192、ruit juice.UV light is possible to use for some freshly squeezed clear juices for chilled distribution.30 General Specific microbial inactivation data UV has been used successfully to increase the shelf life of refrigerated cider without affecting flavour,with a 2-3-log reduction in cider after expo
193、sure to UV for 54s.Treated cider showed no signs of fermentation,spoilage or changes in flavour up to 35 days when stored at 2.2C,while the control and 13.5 s UV treatment samples were actively fermenting(Guerrero-Beltrn&Barbosa-Cnovas 2004).The presence of small amounts of particulates in a liquid
194、can greatly reduce UV penetration.For UV radiation to be effective in liquids of such high UV absorptivity,the liquid must be in the form of a thin film when it is subjected to UV.In this manner,UV absorption by the liquid is low and bacteria are more likely to be subjected to a lethal dose.Wright e
195、t al.(2000)examined the efficacy of UV light for reducing E.coli O157:H7 in unpasteurized cider.Cider containing a mixture of acid-resistant E.coli O157:H7(6.3-log cfu/ml)was treated using a thin-film UV disinfection unit at 254nm.Dosages ranged from 94 to 610 J/m2.The treatment significantly reduce
196、d E.coli O157:H7.and the mean reduction was 3.81-log cfu/ml.The reduction was also affected by the level of background microflora in the cider.With the equipment used in this study,the FDA requirement for a 5-log reduction would not likely be met using UV light alone.Germicidal effects of UV light o
197、n milk have been reported by various authors.Reinemann et al.(2006)got 3 log-reductions on total viable count at a dose of 15 mJ/ml.At 1000 mJ/ml 0.1-1.0 log reductions were reported for Mycobacterium avium ssp.Paratuberculosis in milk(Altic et al.2007;Donaghy et al.2009).Cilliers(2015)measured 3.0
198、log reductions on mesophilic aerobic bacteria in milk at 1500 mJ/ml.Rossitto et al.(2012)established D-values of 330-1430 mJ/ml for various pathogens and spore formers in milk.To have an effect on spores,a higher UV dose is needed.A UV dose of 23.72 J/ml(23720J/L)reached 2.25,2.93,3.24,3.85 and 4.05
199、-log reductions of Bacillus coagulans,Bacillus cereus,Alicyclobacillus acidocaldarius,Bacillus licheniformis and Geobacillus stearothermophilus spores,respectively,in water suspensions(Gayn et al.2013).This study provides the UV dose required for 1-log reductions for several different microorganisms
200、.It also compares different UV doses to three different heat treatments intended for sugar syrup for beverage production.Viruses At present,there is limited information regarding the control of food-borne viruses in foods.In a study conducted by Sansom and Bayliss(2017),two species of bacteriophage(
201、MS2 and FX174)were identified for use as virus surrogates to assess the effect of food safety control measures on the infectivity of viruses.UVC treatment of blueberries,water and stainless-steel coupons contaminated with the two bacteriophages were evaluated.Results from this trial indicate that le
202、vels of MS2 and FX174 can be considerably reduced by the application of UV to various contaminated matrices.However,further work is needed to confirm if this applies across other virus types.31 General Adenovirus is the most UV-resistant virus known.Treatment of approximately 104 Ad41 with different
203、 doses of 254 nm germicidal UV radiation has shown that at UV doses of 225 mJ/cm2 or higher,no virus infectivity(measured by detectable mRNA)was detected(Linden and Sobsey 2004).Chemical effect UV light can accelerate the development of rancidity in products containing unsaturated fatty acids(Matak
204、et al.2007).UV treatment has been reported to not show any inactivation of Polymethyl Esterase(PME),the enzyme responsible for cloud loss leading to quality defects,in orange juice(Torkamani&Niakousani 2011).The effect of UV light on water and fat-soluble vitamins in cow and goat milk showed that an
205、 exposure to 12.6 J/ml lowered the amounts of vitamins in the milk(Guneser and Yuceer,2012).Vitamin C was most sensitive,followed by vitamins EAB2.The effect of UV light on the vitamins was equal or larger than the effect of pasteurization,depending on type of vitamin.The UV dose used in this invest
206、igation was high and comparable to the dose needed to inactivate bacterial spores.At Tetra Pak,we evaluated the UV dose impact on sensory changes in milk(DR0030427).Significant sensory changes were recorded after an irradiation dose of 300 J/ml and at 600 mJ/ml,the milk was deemed undrinkable.These
207、doses were compared to results in literature on doses needed to reach a certain log reduction on microorganisms.In studies where viable bacteria are investigated,the given dose values are in the range up to 1500 mJ/ml.A dose of 1000 mJ/ml yielded a log reduction of 0.1-1 on Mycobacterium avium ssp p
208、aratuberculosis.(Altic et al.2007).Suitable products Applications include disinfection of water supplies and food contact surfaces.Suitable products are clear or almost clear liquids such as clear apple juice and cider.Recently,interest has increased in using UV to reduce microbial counts in juices.
209、UV light can be used for disinfection of clear sugar syrups for production of beverages(soft drinks,still drinks,etc.).Opportunity UV treatment can be used to sterilize water that is used for reconstituting high-acid beverages,thereby cutting down the beverage volume that must be pasteurized(Tetra P
210、ak 2019).Advantages There are no reported changes in physical characteristics of the food matrix.The technology has low capital and maintenance costs.32 General Disadvantages The transmittance of UV light can be reduced by background microbial populations in liquids along with particulates and organ
211、ic matter.UV light can accelerate the development of rancidity in products containing unsaturated fatty acids.Very short penetration depth,product has to be treated in thin sheets.Milk is a highly opaque product and thus the UV penetration depth is very low.Milk also quickly changes in both smell an
212、d taste when treated by UV light(Bandla et al.2012).The irradiation induces chemical reactions in the milk that consumes dissolved oxygen.Thus UV treatment as a stand-alone technology is not likely to replace traditional pasteurization or sterilization of consumption milk.On the other hand,SurePure(
213、http:/ commercial systems for UV treatment of wine,juice and milk.Their equipment for milk was approved in India 2013 to be used instead of pasteurization of milk.No UV-treated consumption milk products have,to our knowledge,appeared in the Indian market.In January 2016,the European Food Safety Auth
214、ority stated that cows milk treated by SurePures UV light purification technology after pasteurization,in order to extend the shelf life of the milk,is safe under the intended conditions of use.SurePure has also tested UV treatment on coconut water.Summary UV treatment is commercialized and widely u
215、sed for water.UV treatment can be used for clear freshly squeezed fruit juices,but the process must be optimized for every product.UV treatment is not suitable to use for juices containing fibres and pulp based on current data.In the dairy segment,UV treatment cannot be used as a standalone method t
216、o replace traditional pasteurization,but may be useful in treatments that extend shelf life.The possibility to use UV treatment as replacement of traditional pasteurization(with heat)needs to be further investigated on effect on milk quality and cost saving.Studies indicate there is also a potential
217、 to use UV treatment for whey and brine,but further investigations are needed.UV light can be used to disinfect clear sugar syrups,or water used in blending,for beverage production(soft drinks,still drinks,etc.),for pasteurization of apple cider,and to some extent for other fruit juices(Tetra Pak 20
218、19).The use of UV light must be optimized for every individual food product,due to the variation in penetration ability of the UV light.33 General IRRADIATION Other names Process Exposes the food to gamma rays,x-rays or electrons.Effect Microbial inactivation is thought to happen through two main me
219、chanisms:direct interaction of the radiation with cell components and indirect action from radiolytic products,such as the water radicals.Advantages Energy use is low.Can achieve microbial inactivation equivalent to pasteurization.Disadvantages Limited enzyme inactivation.Can cause organoleptic chan
220、ges at high doses.Very few foods can take the high dose needed to sterilize it without severe quality degradations.Product focus Used on spices,seeds,shellfish,cereals,rice,fruit and vegetables.Cost index Not investigated.Commercialization It is legally approved to be used on specified products Oppo
221、rtunity Potential to be used on grains and nuts as added ingredients.Food irradiation is a cold process for preserving food that has been well studied for many years.It is used in more than 50 countries(Ravindran and Jaiswal 2019,Roberts 2016)to destroy bacteria and pests and to extend the shelf lif
222、e of food.Irradiation has been used to treat food since the late 1950s and provides processors with an alternative to chemical and heat treatments.Research has shown that food irradiation is safe and effective.The process has been examined thoroughly by the World Health Organization;the United Natio
223、ns Food and Agriculture Organization;the International Atomic Energy Agency;the European Community Scientific Committee for Food;the United States Food and Drug Administration;a United Kingdom House of Lords committee,by scientists at Food Standards Australia and New Zealand(FZANZ),and others(see va
224、rious website links in the reference list).History Research on food irradiation goes back over a hundred years.The idea of using ionizing radiation in food preservation almost immediately followed Henri Becquerels discovery of radioactivity in 1895.The suggestion to use ionizing energy to destroy pa
225、thogenic and spoilage microorganisms in food was published in a German medical journal the same year.The first U.S.and British patents were issued for use of ionizing radiation to kill bacteria in foods in 1905.The modern era of food irradiation applications research began in 1950,when the United St
226、ates Atomic Energy Commission(USAEC)initiated a coordinated research programme on ionizing radiation for food preservation.To establish the safety and effectiveness of the irradiation process,the U.S.Army began a series of experiments with fruits,vegetables,dairy products,fish and meats.34 General T
227、he first commercial use of food irradiation occurred in 1957 in Stuttgart,Germany,when a spice manufacturer decided to improve the hygienic quality of his product.Operating principle Food irradiation physically exposes pre-packaged or bulk foodstuffs to gamma rays,x-rays or electrons.The degree of c
228、hemical and physical change produced when food is exposed to high-energy irradiation is determined by the energy absorbed.The absorbed dose is measured in units of kilogray(kGy)where one gray is the energy absorption of one joule/kg.The unit rad(1 rad=0.01 Gy)was widely used in the past.Low-dose tre
229、atment,up to 1 kGy for disinfection effects,is used for inhibiting sprouting and controlling insects.Medium doses,1-10 kGy for pasteurization effects,are used to reduce or inactivate pathogenic bacteria and spoilage bacteria.Generally,the upper limit approved for food irradiation is 10 kGy.With high
230、 doses,over 25 kGy,food can be commercially sterilized and given to hospital patients who have immune system deficiencies.Irradiation has proven to be extremely beneficial in terms of prolonging fruit and vegetable shelf life by 3-5 times.Microbiological effect An expert group within FAO/WHO conclud
231、ed that irradiation of foods with an absorbed dose up to 10 kGy causes no toxicological hazard and introduces no special nutritional or microbiological problems.Microbial inactivation by all types of ionizing radiation is thought to occur through two main mechanisms:direct interaction of the radiati
232、on with cell components and indirect action from radiolytic products,such as the water radicals.Viruses,bacterial spores,and some mould and yeasts are more resistant to irradiation.Doses between 1.5-4.5 kGy typically kill vegetative cells of bacterial pathogens,but higher doses are required to inact
233、ivate spores and viruses.In a study E.coli O157:H7 were transferred to clarified apple juice and irradiated at 2C with a cesium-137 irradiator.A dose of 1.8 kGy should be sufficient to achieve a 5-log inactivation(Buchanan et al.1998).Juices with high levels of suspended solids required a higher dos
234、e of radiation than clear juices.The minimum dose that is required to achieve the intended effect must be established for each specific food product.Chemical effect Irradiation affects different foods in distinct ways.It breaks long molecules,such as cellulose,into shorter carbohydrates.Some fruits
235、and vegetables become soft and lose some of their characteristic texture when irradiated.The irradiation of fats creates free radicals that oxidize fats and leads to rancidity.High dosages of irradiation can produce intense off-flavours resembling burnt feathers from 35 General oxidation or related
236、off odours.Irradiation can break down proteins and destroy a portion of some vitamins,particularly A,B,C and E.Since milk and dairy products are major sources of vitamins A and E,these foods are generally not suitable for irradiation(Ravindran and Jaiswal 2019).Investigations on how to apply irradia
237、tion to dairy products are on-going(Odueke et al.2018).Ultra-short,high-intensity radiation treatments result in higher local radical concentrations and favour radical-radical recombination reactions.This reduces the diffusion of radical species,which are thought to be responsible for undesirable ef
238、fects of irradiation on food quality.Use of irradiation to preserve fruit juices is limited because of its effects on the characteristics and organoleptic qualities.Combining processes often inhibits the development of undesirable sensory and chemical changes in foods.Gamma irradiation(10 kGy)causes
239、 beany and paint-like flavours in sweetened orange juice.Incorporation of 0.134%potassium sorbate before irradiation completely prevents the formation of irradiation-induced sensory changes and diminished the rate of browning and ascorbic acid losses during irradiation and storage.Suitable products
240、The FDA has approved a variety of foods for irradiation in the United States:Beef and pork Crustaceans(e.g.,lobster,shrimp,and crab)Fresh fruits and vegetables Lettuce and spinach Poultry Seeds for sprouting(e.g.,for alfalfa sprouts)Shell eggs Shellfish molluscs(e.g.,oysters,clams,mussels,and scallo
241、ps)Spices and seasonings Foods and food ingredients authorized for irradiation in the EU are currently:Fruit and vegetables including root vegetables Cereals,cereal flakes,rice flour Spices,condiments Fish,shellfish Fresh meats,poultry,frog legs Raw milk camembert Gum arabic,casein/caseinates,egg wh
242、ite Blood products 36 General There are seven food categories that may be irradiated in the UK:Fruit and vegetables Cereals Bulbs and tubers Dried aromatic herbs,spices and vegetable seasonings Fish and shellfish Poultry Advantages Irradiation can be applied to foods in small packages or in bulk,in
243、a frozen state or at room temperature,with great versatility in applications.The treatment in many cases occurs after packaging,thus avoiding recontamination.Compared with the energy required for canning,refrigeration,or frozen storage,the energy used for irradiation preservation of food is small.Di
244、sadvantages Very few foods can take the high dose needed to sterilize it without severe quality degradations.Milk,for example,becomes undrinkable at about one hundredth of the dose needed to sterilize it.A clear disadvantage of irradiation compared to thermal processing is the lack of enzyme inhibit
245、ion in foods,even by high-dose irradiation required for commercial sterilization.Another disadvantage of food irradiation is its name.For many consumers ionizing radiation evokes unpleasant associations of radioactivity,nuclear threats,high technology,genetic mutation,and cancer.Like other physical
246、processes,irradiation requires large capital costs and critical minimum capacities and product volumes for economic operation.However,unlike other physical processes,irradiation-operating costs are small,especially with regard to energy requirements.Summary Irradiation can achieve a microbial effect
247、 that is equivalent to thermal pasteurization.It can be used for a variety of foods,but its use is limited for some products,such as dairy products,due to negative organoleptic changes.International agencies WHO and IAEA,as well as the FDA in the US,have approved food irradiation as a safe and effec
248、tive technique to ensure food safety The FDA requires irradiated foods to bear the international symbol for irradiation the radura shown in Figure 2 and carry the statement Treated with radiation or Treated by irradiation on the food label.37 General Figure 2.Radura,symbol of irradiated foods The EU
249、,Australia and New Zealand regulations require treated food to be labelled with text indicating that the food in the package has been irradiated.In Canada and Malaysia labelling is not required if the irradiated ingredient is less than 5%and 10%by weight,respectively(Roberts 2016).38 General MICROFI
250、LTRATION Other names Membrane filtration is the“umbrella name”for microfiltration,ultrafiltration,nanofiltration and reverse osmosis Process A porous membrane is used to remove microorganisms.Can be both crossflow and dead-end configuration Effect Microorganisms are physically removed from a liquid.
251、Advantages Gentle treatment that can be made at room temperature or lower.Can be used for fractionation Disadvantages In crossflow microfiltration,sometimes one stream is waste.For production of ESL milk only skimmed milk can be used and it must be combined with heat treatment for pasteurization.Lon
252、g CIP times.Product focus Widely used within the food and beverage industry:production of cheese milk,ESL milk,concentration of milk for cheese production,whey handling,treatment of fruit and berry juices,and wine.Cannot be used for liquids with particulates.Cost index Depends on application Commerc
253、ialization For liquid food,water and pharmaceuticals Opportunity A well-developed technology that can be further optimized.If a sterile filtration is performed,i.e.removal of all microorganisms,the process could replace a heat treatment.History In 1855,Adolf Fick published his phenomenological law o
254、f diffusion(Fick 1855),which we still use today as a first-order description of diffusion through,for example,membranes.Although many of the scientific milestones in membrane technology occurred before the 1930s,the membrane-based industry did not emerge until the 1950s(Lonsdale 1982).A landmark eve
255、nt in membrane technology was the development of the synthetic asymmetric membrane in 1959 by Loeb and Sourirajan at the University of California,Los Angeles(Loeb and Sourirajan 1963).In the late 1960s ultrafiltration enjoyed a major breakthrough with the development of non-cellulosic asymmetric ult
256、rafiltration membranes with improved thermal and chemical resistance.Cheese-making using membrane technologies commenced in the late 1960s but the wider breakthrough of microfiltration in the dairy industry came in the 1980s with the development of new ceramic membranes comprising a multi-channel ge
257、ometry and highly permeable support.Crossflow microfiltration has since evolved as an industrial separation technology in areas such as bacteria removal,defatting of whey,and micellar casein enrichment of cheese milk(Maubois 1997).39 General Operating principle Membrane filtration can be configured
258、as either dead-end filtration or crossflow filtration.The difference between them lies in their names.In the dead-end process there is a feed stream and a permeate stream,the stream that has passed through the membrane filter.All components retained by the membrane filter stay on the surface of the
259、membrane filter,and a filter cake builds up,becoming thicker and thicker.In crossflow membrane filtration there is a feed stream,a permeate stream and a retentate stream,which contains the components that do not pass through the membrane filter.The retentate stream sweeps away the retained component
260、s,keeping the thickness of the filter cake constant(see Figure 3).The advantage of crossflow membrane filtration to dead-end is that the running-time and capacities are greater,and it is a continuous process.Figure 3.Dead-end and crossflow membrane filtration The driving force in a membrane process
261、can be a pressure difference,a difference in concentration,an electrical potential difference or a difference in partial pressure.Within Tetra Pak we work only with pressure-driven processes.Pressure-driven membrane filtration processes can be divided into microfiltration(MF),ultrafiltration(UF),nan
262、ofiltration(NF)and reverse osmosis(RO).The differences between these four membrane processes are the size of the particles,molecules or solutes retained by the membrane,the pressure difference used and the pore size and porosity of the membrane.There is no strict border between the different process
263、es,but Figure 3 gives an idea of their separation range.40 General Table 3.The ranges of pressure-driven membrane processes Membrane process Driving force Separation range Microfiltration 0.01-0.1 MPa Pore size 0.1-10 m Ultrafiltration 0.1-1 MPa Cut-off 1-500 kDa(0.001-0.1 m)Nanofiltration 0.5-2 MPa
264、 Cut-off 300Da,pore-size 0.1-10 nm,NaCl retention 6.5 Maubois 1997 Listeria innocua 1.99 3.3 Maubois 1997 Listeria 1.9 3.2 Maubois 1997 Listeria monocytogenes 0.4-0.5 m width 0.2-2 m length 3.4 Saboya and Maubois 2000 Citrobacter 3.1 5.7 Maubois 1997 7 species average 2.6 Trouv et al.1991 Brucella a
265、bortus 0.5-0.7 m width.0.6-1.5 m length 4 Trouv et al.1991 Mycobacterium tuberculosis 0.3-0.6 m width.1-4 m length 3.7 Trouv et al.1991 Salmonella typhimurium 0.7-1.5 m width.2-5 m length 3.5 Trouv et al.1991 Salmonella abortusovis 2.5 Madec et al.1992 Total count 3.3-4.2 Sachdeva et al.2001 Total c
266、ount 2.7 Customer site Total count 4 Eino 1997 Somatic cells 7-12 m complete reduction te Giffel and van der Horst 2004 43 General Different bacteria of equal size may behave differently during filtration,due to their ability to deform.Gram-positive bacteria are less deformable than gram-negative ba
267、cteria and are more effectively rejected(Lebleu et al.2009).It has been shown that the impact of TMP on particle retention in dead-end microfiltration is strongly correlated to particle stiffness/resistance to deformation(Helling et al.2017,Gaveau et al.2017).Chemical effect The chemical effect depe
268、nds on the pore size of the membrane being used and on the product being processed.For protein fractionation of milk,for example,the purpose is to fractionate casein and whey proteins,which of course leads to two products with different chemical compositions.The process of removing spores from skim
269、milk for cheese milk production does not have any significant impact on the chemical composition of the milk.Suitable products Membrane filtration is widely used within the food and beverage industry.Examples are production of cheese milk,ESL milk,concentration of milk for cheese production,whey han
270、dling,treatment of fruit and berry juices,and wine.The technology cannot be used for liquids with particulates.Advantages Membrane filtration is in general a gentle treatment method and it can be done at room temperature or lower if required.Disadvantages One disadvantage of crossflow filtration is
271、that it is normally only one of the streams that are of interest.The other stream is often regarded as a waste.Another disadvantage with membrane filtration is the fouling that occurs on the membrane surface and inside the pores.This fouling affects the capacity of the process and can also affect th
272、e membranes ability to permeate different components.The fouling has to be removed by CIP,which in some cases can be quite time-consuming.For application removal of microorganisms to extend shelf life of milk,skim milk must be used since the fat globules will not pass through the membrane.Summary Me
273、mbrane filtration is a well-developed commercial process that can be used for many applications,such as fractionation and concentration of milk components and removal of microorganisms.44 General ULTRASOUND Other names Sonication Process Uses energy from sound waves to create cavitation the rapid fo
274、rmation and collapse of vapour bubbles in low-pressure areas.Effect Cavitation produces very high shear energy waves and turbulence that disrupts microorganisms in several ways.Advantages Enhances other technologies,such as heat,for preservation purposes.Disadvantages Extreme local temperatures(up t
275、o 5000C)and pressures(on the order of 50 MPa)might cause problems with product quality.Cannot be used on its own for inactivating microorganisms.The combined process of cavitation and heat needed to inactive microorganisms and enzymes has a higher total energy requirement than heat alone.Free radica
276、ls can be formed that might deteriorate the product quality.Product focus Cost index Not investigated Commercialization Not known to be available for microbial inactivation.Used in degassing,cutting,emulsification,etc.Opportunity Ultrasound combined with heat and/or pressure enhances the inactivatio
277、n of microorganisms,but more studies are required to understand the commercial feasibility.Ultrasound uses energy generated by sound waves.It is thoroughly studied in many applications in the field of food but has limited usage as a standalone for preservation.This is the reason it is often coupled
278、with other decontamination techniques.The most common combinations are:Thermosonication(heat plus sonication)Manosonication(pressure plus sonication)Manothermosonication(heat plus pressure plus sonication).History The use of ultrasound in analysis dates back to 1917.Power ultrasound in processing ca
279、n be traced as far back as 1927,when it was reported that ultrasound was extremely efficient for the production of an oil and water emulsion.The killing potential of ultrasound was discovered when sonar was being investigated for use in anti-submarine warfare,and it was noticed that the sound waves
280、were killing fish.In the 1960s research concentrated on understanding how ultrasound interaction with microbial cells,and in recent years there has been much research on the inactivation of microorganisms and enzymes.45 General Operating principle Ultrasound is energy generated by sound waves of 20,
281、000 Hz or higher.The vibrational energy is provided by ultrasonic transducers that convert electrical energy to sound energy.The most common is the piezoelectric transducer,but magnetostrictive transducers are considered more robust,although less energy-efficient(Tiwari and Mason 2012).Main frequenc
282、ies for ultrasonic processing appear to be in the region 20-25 kHz.The ultrasound induces mechanical,chemical and biochemical effects in liquids via the production and collapse of cavitation bubbles(Paniwnyk 2017).The conditions within the imploding bubbles can be dramatic,with temperatures of 5,000
283、K and pressures on the order of 50 MPa(Tiwari and Mason 2012,Loraine et al.2012).This in turn produces very high shear energy waves and turbulence in the cavitation zone.One of the main benefits is the absence of moving parts(Patist and Bates 2008).Microbiological effect The bactericidal effect of u
284、ltrasound can be grouped into different classes(Tiwari and Mason 2012,Evelyn and Silva 2015):Bacteria cell wall damage Shear forces Localized heating Chemical attack due to formation of free radicals The major bactericidal effect is attributed to intracellular cavitation,micromechanical shocks that
285、disrupt cellular structural and functional components up to the point of cell lysis(Tiwari and Mason 2012).The use of ultrasound alone to lyse microbial cells is a well-established laboratory method to extract intracellular components.Thinning of the cell membrane may occur due to the localized heat
286、ing and production of free radicals by sonolysis of water.The effectiveness of ultrasound in inactivating microorganisms is dependent on the composition of the food matrix.This becomes quite evident when comparing results from ultrasound-treated microorganisms suspended in buffer to microorganism pr
287、esent in a food system:a 10-minute treatment reduced populations of salmonellae by 4-log cycles in peptone water;while a 30-min treatment of chocolate milk only lowered the population by 0.8-log cycle(Piyasena et al.2003).The reduction of Bacillus cereus spores by thermosonication in skim milk was m
288、uch lower(less than 0.5-log),compared to when the spores were present in beef or cheese slurry,and rice porridge(3-4-log)(see Figure 5).This could be explained by a sonoprotective effect of lactose(Evelyn and Silva 2015).Studies have also shown an increased effect of ultrasound when the total solid
289、content increases.Evelyn and Silva(2018)further report that thermosonication at 70C/1.5 min was more effective on B.cereus spores than the heat treatment alone(70C/1.5 min).It seems like the viscosity or consistency of the food has a higher impact on spore inactivation by thermosonication than by th
290、ermal treatment alone.46 General A pre-treatment with ultrasound before the heat treatment does not seem to have the same positive effect as thermosonication(Ansari et al.2017).Figure 5.Psychrotrophic B.cereus spore log reduction in different foods after thermosonication(24 kHz,210 m,0.33 W/ml or W/
291、g)(Evelyn and Silva 2015).Sonication alone has been reported to be less effective on gram-positive bacteria and spores(Tiwari et al.2012)and combination with other treatments is needed.In general,bacterial cells become more sensitive to heat treatment if they have undergone thermosonication:ultrasou
292、nd treatment in combination with heat.Critical processing parameters of ultrasound are the amplitude of the ultrasonic waves,the exposure time with the microorganisms,the type of organism,the volume of food to be processed,the composition of the food as well as treatment temperature.Chemical effect
293、High-intensity ultrasound produces several changes in food,mainly through the effects of cavitation.Energy released may cause chemical reactions due to free radicals,which can result in cell membranes becoming more permeable and vulnerable to harmful substances.The production of free radicals can be
294、 an advantage with some foods but might also have a negative effect on the flavour of fruit drinks and high-fat foods,such as dairy products.In a study of ultrasounds impact on milk components,the fat content as measured by MilkoScan increased(Cameron et al.2009).This was due to fat globules being d
295、isrupted into smaller droplets.Disrupting the fat globules might increase the amount of free fatty acids and the risk for rancid taste.The amount of free fatty acids was not measured in the study.In the same study it was also seen that the protein content measured with MilkoScan also increased after
296、 ultrasonication.47 General This could be due to the disruption of the casein micelles.If this was the case,there is an increased risk for proteolysis and bitter taste.Somatic cells were also lysed by the ultrasonication,which causes the release of proteases and lipases present in the cells and risk
297、 for increased breakdown of milk components during storage.Thermosonication is reported to be effective in inactivating enzymes such as PME(pectin methylesterase),POD(peroxidase)and PPO(polyphenol oxidase),although they have different resistances(Anya-Esparza et al.2017,Sanz et al.2018).Pre-treatmen
298、t of green coconut water with ultrasound before heat treatment gave a higher inactivation of the enzyme peroxidase(Rojas et al.2017).Pectin methylesterase was more resistant to thermosonication than polyphenol oxidase(Illera et al.2018).Combining pressure treatment with heat and ultrasound treatment
299、(mano-thermosonication)was found to be more effective than heat treatment alone in the inactivation of heat resistant proteases and lipases produced by P.fluorescens(Tiwari and Mason 2012).Suitable products The effect of the treatment depends on the food matrix.Products without fibres and particulat
300、es are likely more suitable.Other applications of ultrasound in food processing According to Chemat et al.(2011),ultrasound technology has a wide range of current and future applications in the food industry,including:Cooking Freezing/crystallization Drying Degassing Defoaming Emulsification Cutting
301、 The rheological and textural properties of set-style yoghurt were improved when made from milk that had been treated with thermosonication(Riener et al.2010).Advantages A potential advantage is that it can be used to enhance other technologies,such as heat.Disadvantages Ultrasound alone lacks the p
302、ower and versatility to inactivate microorganisms reliably for purposes of food preservation.Combining ultrasound with the heat needed to inactivate microorganisms and enzymes has a higher total energy requirement than heat alone.48 General Free radicals can be formed that might deteriorate the prod
303、uct quality.There is a risk that particulates and fibres can be destroyed.The very high local temperatures during cavitation might cause problems with product quality.Summary Ultrasound or sonication alone is not very effective at killing microorganisms in food.Ultrasound in combination with heat an
304、d/or pressure enhances the inactivation of microorganisms and might have potential for commercial applications.However,more studies are required to understand the commercial feasibility of such process.49 General HYDRODYNAMIC CAVITATION Other names Process Cavitation is generated by the liquid passi
305、ng through a constriction such as a throttling valve,an orifice plate,etc.Effect Bactericidal effect is due to cavitation(see Ultrasound)Advantages Potential enhancer of other technologies,such as heat,for pasteurization purposes.Energy efficiency 10-100 times better than ultrasonic systems.Disadvan
306、tages Extreme local temperatures(up to 5000C)and pressures(around 50 MPa)might cause problems with product quality.Cannot be used on its own for inactivating microorganisms.The combined process of cavitation and heat needed to inactivate microorganisms and enzymes has a higher total energy requireme
307、nt than heat alone.Free radicals can be formed that might deteriorate the product quality.Risk that particulates and fibres can be destroyed.Product focus Cost index Commercialization not known to be available for microbial inactivation.Used in scale-free heating,emulsification,mixing,powder hydrati
308、on.Opportunity potentially the same as for Ultrasound Operating principle Hydrodynamic cavitation differs from ultrasonic cavitation in how the cavitation is generated.In ultrasonic cavitation a high-frequency sound generates cyclic pressure waves in the liquid,and this drives the cavitation(Loraine
309、 et al.2012,Mohammadi et al.2014).In hydrodynamic cavitation,the cavitation is generated by the passage of the liquid through a constriction such as a throttle valve,an orifice plate,etc.(Parag et al.2005,Loraine et al.2012).The cavitation is generated by passage of the liquid through a constriction
310、 such as a throttling valve,an orifice plate,etc.When the liquid passes through the constriction the velocity increases and pressure decreases.When the pressure falls below the threshold pressure for cavitation,millions of cavities(bubbles)are formed(Gogate and Pandit 2005).The threshold pressure is
311、 usually the vapour pressure of the medium at a specific operating temperature.The magnitude of the pressure depends on the geometry of the constriction and the flow conditions of the liquid.When the liquid jet expands again,the pressure is recovered and the cavities collapse.The collapse of a cavit
312、y/bubble results in extreme local temperature,up to 5,000C,and pressure up to around 50 MPa(Loraine et al.2012).50 General Microbiological effect As with ultrasound/sonication,the bactericidal effect is due to cavitation and can be grouped into different classes(Tiwari and Mason 2012,Evelyn and Silv
313、a 2015):Bacteria cell wall damage Shear forces Localized heating Chemical attack due to formation of free radicals.Loraine et al.(2012)also found that gram-positive bacteria are more resistant to hydrodynamic cavitation than gram-negative;E.coli was more easily killed than B.subtilis.The time to rea
314、ch a 5-log reduction on E.coli depended on the orifice and pressure conditions and varied between 60 180 minutes.That study does not state at which temperature the experiments were conducted but indicates that it was controlled by a cooling coil,so presumably the temperature was much lower than duri
315、ng normal heat treatment.Chemical effect Since the principle is to create cavitation,the chemical effects are the same as when using ultrasound/sonication.The energy released during cavitation may cause chemical reactions due to free radicals,which can result in cell membranes becoming more permeabl
316、e and vulnerable to harmful substances.The production of free radicals can be an advantage with some foods,but might also have a negative effect on the flavour of fruit drinks and high-fat foods,such as dairy products.Applications Edible oil refining Petroleum upgrading Wine aging and beverage enhan
317、cement Water treatment Biodiesel transesterification Biomass and biofuels Scale-free heating Mixing Extraction Emulsification Powder hydration Patel Hasmuck(2017)from Land OLakes indicated there were no applications yet within dairy industry.Land OLakes has explored hydrodynamic cavitation within:51
318、 General Mixing and hydration,Texture management in Greek yogurt and smoothies,viscosity reduction,scale-free and uniform heating of viscous liquid,microparticulation of whey protein,emulsion formation and microbial inactivation.Summary Hydrodynamic cavitation alone is not very effective at killing
319、microorganisms in food.Cavitation in combination with heat and/or pressure enhances the inactivation of microorganisms,but more studies are required to understand its commercial feasibility.52 General PULSED ELECTRIC FIELD Other names not known Process The food to be treated is placed between two el
320、ectrodes and it is based on short electrical pulses at high electrical voltage.Critical parameters are electric field strength,pulse frequency and shape and initial product temperature.Effect The widely accepted hypothesis is that the field created between the electrodes charges the bacterial cell w
321、all causing damage to the cell,known as electroporation.Advantages PEF technology can easily be incorporated into a pasteurizer for flexibility.Can handle fibres and particles,to some extent.Disadvantages Only for pasteurization.Product focus Liquid and semi-liquid food products Cost index Productio
322、n cost about 2.5 higher than thermal treatment and investment cost about 7 times higher.Commercialization For pasteurization of fruit juices and in processes such as blanching,extraction,drying and frying.Opportunity Any advantage would be at first pasteurization of fruit juices.PEF can be used for
323、liquid and semi-liquid food products for pasteurization.It is also applied in processes such as extraction,blanching,drying and frying.Potatoes can be made softer and easier to cut in manufacturing chips and french fries,for example.The application of PEF is restricted to food products that can with
324、stand electrical fields,have low electrical conductivity,and do not contain or form bubbles.History At the end of the 19th century,the bactericidal effects of direct and alternating electrical current were investigated for the first time by Prochownick and Spaeth.A process called“Electropure”was int
325、roduced in Europe and the US in the 1920s.This was one of the first attempts to use electricity for milk pasteurization(Toepfl et al.2007).PEF started to be applied to food processing in the middle of the 20th century and was invoked by the discovery of electroporation.The first experiments using PE
326、F for killing microorganisms were reported in the 1960s(Sitzmann et al.2016).In the late 1980s early 1990s an industrial-scale plant for rendering fats from slaughterhouse products in Germany and low-temperature production of fish meal in Norway were commissioned.The concept of applying very intensi
327、ve electric field pulses to inactivate microorganisms in foods was patented by Maxwell laboratories in the mid-1980s and developed to pilot plant scale in cooperation with an American PEF consortium.53 General However,the inactivation of microorganisms by PEF was more complex than expected and the a
328、ctivity was closed down in 2002(Lelieveld et al.2007).In 1995,a letter of no objection was released by the FDA for the use of PEF technology for food preservation(Toepfl et al.2007).Operating principle The food to be treated is placed between two electrodes,one high-voltage and the other ground/eart
329、h.Up to several hundred electric pulses are applied over the electrodes.There is no definitive evidence on what mechanisms are involved,but the widely accepted hypothesis is that the field created between the electrodes charges the bacterial cell wall causing damage to the cell,known as electroporat
330、ion.The pulses are in the range of microseconds.The critical process parameters of PEF technology are electric field strength,pulse width/length,pulse shape,pulse frequency,pulse polarity and initial temperature.PEF can also be combined with elevated temperature,as this increases the effect on the r
331、eduction of bacteria(Sharma et al.2014).Microbiological effect The degree of inactivation of microorganisms by PEF is greater at increases in electric field strength,pulse frequency and pulse duration.In addition,factors like pulse width and pulse shape influence microbial inactivation.Bipolar pulse
332、s were reported to be generally more effective compared to monopolar pulses.Other factors include the temperature of the food,its pH,ionic strength and electrical conductivity of the food matrix.The reported target organisms have been Bacillus subtilus,E.coli,E.coli O157:H7,Lactobacillus spp.,Lister
333、ia spp.,Pseudomonas spp.,Salmonella spp.,Staphylococcus aureus,Listeria innocua,Saccharomyces cerevisiae and Yersinia enterocolitica.The media tested have included milk,fruit and vegetable juices,tea and buffer at different conductivity levels and pH similar to foods.Some articles(Roobab et al.2018)report that vegetative cells are inactivated at field strengths around 10-15 kV/cm but the majority