Recent Advances in the Use of High Pressure as an Effective Processing Technique in the Food Industr

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  Recent Advances in the Use of High Pressure as an EffectiveProcessing Technique in the Food Industry Tomás Norton  &  Da-Wen Sun Received: 27 May 2007 /Accepted: 17 July 2007 / Published online: 25 September 2007 # Springer Science + Business Media, LLC 2007 Abstract  High pressure processing is a food processingmethod which has shown great potential in the foodindustry. Similar to heat treatment, high pressure processinginactivates microorganisms, denatures proteins and extendsthe shelf life of food products. But in the meantime, unlikeheat treatments, high pressure treatment can also maintainthe quality of fresh foods, with little effects on flavour andnutritional value. Furthermore, the technique is independent of the size, shape or composition of products. In this paper,many aspects associated with applying high pressure as a processing method in the food industry are reviewed,including operating principles, effects on food quality andsafety and most recent commercial and research applica-tions. It is hoped that this review will promote morewidespread applications of the technology to the foodindustry. Keywords  Highpressure.HPP.HPLT.Lowtemperature.Inactivation.Enzyme.Microorganism.Shelflife.Foodquality.Foodsafety.Freezing.Thawing Nomenclature  P   pressure (Pa) T   temperature (°C) ρ  density (kg m − 3 ) η   viscosity (Pa s) C   p  specific heat (W kg − 1 K  − 1 )  D  characteristic length (m) k   inactivation constant  λ  thermal conductivity (W/m 1 K) t   time α  thermal expansion coefficient (K  − 1 )  A, B, C   mass of each designated food component  CH   compression heating (°C) Subscripts M food mediumW water  p food product  pp food product packaginghyd_me hydraulic mechanisms in processing mediumhyd_p hydraulic mechanisms in product th_me thermal conduction in processing mediumth_p thermal conduction in food product th_pp thermal conduction in product packagingin inactivationx, y, z designated food component food composite food material Introduction Food processing involves synergism between different  physical processes to transform raw animal/plant materialsinto consumer-ready products. Today, the food industry isexpected to prevent or reduce negative changes in foodquality over time to provide a wide variety of food rich incolour, texture and flavour and to adapt and develop newfood processes to satisfactorily meet the requirements of awide demographic within different cultures. Without food Food Bioprocess Technol (2008) 1:2  –  34DOI 10.1007/s11947-007-0007-0T. Norton : D.-W. Sun ( * )Food Refrigeration and Computerised Food Technology Group,University College Dublin, National University of Ireland,Earlsfort Terrace,Dublin 2, Irelande-mail: dawen.sun@ucd.ieurl:;   processing, these goals could not be upheld, as food couldneither be transported over long distances nor stored fromtime of plenty to time of need (Lund 2002).In the present day, consumers judge food quality basedon its sensory and nutritional characteristics (e.g. texture,flavour, aroma, shape and colour, calorie content, vitaminsetc.), and alongside shelf life, these now determine anindividual ’ s preference for specific products. Consequently,retailers are reporting up to a 30% growth in fresh, chilledand healthy food sales (Hogan et al. 2005). US sales in pre-cut salad mixes were $1.9 billion in 2001 and increased to$2.11 billion in 2003 (Hodge 2003). However, the recent upsurge in demand has presented challenges to the foodindustry, mainly in implementing techniques to keep foodfresher for longer, whilst offering a reasonable shelf life andconvenience and assuring food safety. Owing to recent consumer preferences, impetus has been given to thedevelopment of concept-driven novel technologies that  provide the required processing through non- or mildlythermal means (Welti-Chanes et al. 2005). Accordingly,much of the recent scientific research for the food industryhas focused on non-thermal processing techniques, withhigh pressure processing (HPP) being amongst the fewexperiencing great potential in commercial settings (Sun2005).Food safety and shelf life are often closely related tomicrobial quality and other phenomena such as biochemicalreactions, enzymatic reactions and structural changes, andthus, although often indirectly, can significantly influenceconsumers ’  perception of food quality (LeBail et al. 2003).Physical (e.g. heating, freezing, dehydration and packaging)and chemical (e.g. reduction of pH or use of preservatives) preservation methods continue to be used extensively(Manas and Pagan 2005). Conventional thermal sterilisa-tion processes are the most commonly used methods of food preservation and involve heat transfer from a process-ing medium to the slowest heating zone of a product andsubsequent cooling. Thus, although being effective mech-anisms for microbial inactivation, thermal processes can permit changes in product quality and cause off-flavour generation, textural softening and destruction of coloursand vitamins, the extent of which is dependent on the product being treated and the temperature gradients between food and process boundaries. Microbial inactiva-tion provided by HPP mainly targets cell membranes of treated cells, but in some cases, additional damaging eventssuch as extensive solute loss during pressurisation, proteindenaturation and key enzyme inactivation are also required(Manas and Pagan 2005). The multi-target ability of high pressure (HP) has meant that in situations where its soleemployment yields unsatisfactory results, a high level of synergism can be obtained when combined with other  processing techniques. Effective preservation has beenreported from combinations of HP with pH (Raso andBarbosa-Canovas 2003), HP with pulsed electric fields(Ross et al. 2003) and HP with CO 2  (Spilimbergo et al.2002). Furthermore, when used in conjunction with mildlythermal processes, HP has been found to significantlyincrease the inactivation of bacterial spores (Raso andBarbosa-Canovas 2003).High pressure processing is a technology that potentiallyaddresses many, if not all, of the most recent challengesfaced by the food industry. It can facilitate the production of food products that have the quality of fresh foods but theconvenience and profitability associated with shelf lifeextension (McClements et al. 2001). HPP has already become a commercially implemented technology, spreadingfrom its origins in Japan, followed by USA and nowEurope, with worldwide take-up increasing almost expo-nentially since 2000 (Fig. 1a); although as of yet, this hasnot been homogenous throughout the food industry. HPPcan be applied to a range of different foods, including juicesand beverages, fruits and vegetables, meat-based products(cooked and dry ham, etc.), fish and pre-cooked dishes,with meat and vegetables being the most popular applica-tions (Fig. 1 b). European companies presently employingthis technology include orange juice by UltiFruit®; thePernod Ricard Company, France; and sliced ham byEspuña, Spain; fruit jams by Solofruita, Italy (Urrutia-Benet  2005). Furthermore, as evident in Table 1, a wide variety of companies provide HPP technology to the foodindustry.High pressure processing techniques have also gainedmomentum in areas of food preservation outside of sterilisation and pasteurisation. The range of possibilitiesoffered by combining high pressure with low temperatures(HPLT) has allowed the basis of a new field of HP foodapplications to be formed, such as pressure-supportedfreezing, thawing and subzero storage. Much work has been conducted in the development and optimisation of HPLT processes, and new findings regarding the phasetransitions of water, with consequential benefits for the foodindustry, have recently been revealed (Urrutia-Benet et al.2004).High pressure research and development in different disciplines within the food industry has been recentlyreviewed by some authors (Rastogi et al. 2007; Torres andVelazquez 2005; San Martin et al. 2002; San Martin- Gonzalez et al. 2006; Toepfl et al. 2006). A comprehensive review was conducted by Rastogi et al. (2007) who, as wellas assessing many studies on the effect of HPP on enzymesand proteins, also provided information on the successfuluse of HPP, either solely or in combination with other  processing techniques. Other reviews have focused on theeffect of HPP on microorganisms and food constituents(San Martin et al. 2002); the use of HPP in the dairy Food Bioprocess Technol (2008) 1:2  –  34 3  industry (O ’ Reilly et al. 2001; San Martin-Gonzalez et al.2006; Huppertz et al. 2006); the commercial opportunities and research challenges in HPP (Torres and Velazquez2005); the energy efficiency of HPP (Toepfl et al. 2006) and pressure-assisted freezing and thawing of foods(Cheftel et al. 2002). However, no review has completeda combined study of the modern engineering aspects of HPtechnology alongside its conventional and novel uses in thefood industry. Moreover, the extensive progress made invery recent years in non- and mildly thermal and lowtemperature HPP merits a state-of-the-art review. Conse-quently, this study addresses many of the aspects associatedwith applying high pressure as a processing method in thefood industry, from the engineering principles involved,through food quality and safety issues, to the most recent commercial and research applications, all of which haveseen great development in recent times. Engineering Concepts of HPP The governing principles of HPP are based on theassumption that foods which experience HP in a vesselfollow the isostatic rule regardless of the size or shape of the food. The isostatic rule states that pressure is instanta-neously and uniformly transmitted throughout a samplewhether the sample is in direct contact with the pressuremedium or hermetically sealed in a flexible package.Therefore, in contrast to thermal processing, the timenecessary for HPP should be independent of the samplesize (Rastogi et al. 2007).The effect of HP on food chemistry and microbiology isgoverned by Le Chatelier  ’ s principle. This principle statesthat when a system at equilibrium is disturbed, the systemthen responds in a way that tends to minimise thedisturbance (Pauling 1964). In other words, HP stimulates Fig. 1  (Color online) The num- ber of HP equipment installed inEurope by Hyperbaric® versus a  year of installment and  b  theindustrial sector for the install-ment (Urrutia-Benet  2005)4 Food Bioprocess Technol (2008) 1:2  –  34  some phenomena (e.g. phase transition, chemical reactivity,change in molecular configuration, chemical reaction) that are accompanied by a decrease in volume, but opposesreactions that involve an increase in volume. The effects of  pressure on protein stabilisation are also governed by this principle, i.e. the negative changes in volume with anincrease in pressure cause an equilibrium shift towards bond formation. Alongside this, the breaking of ions is alsoenhanced by HP, as this leads to a volume decrease due tothe electrostriction of water. Moreover, as hydrogen bondsare stabilised by high pressure, as their formation involves avolume decrease, pressure does not generally affect covalent bonds. Consequently, HP can disrupt largemolecules of or microbial cell structures, such as enzymes, proteins, lipids and cell membranes, and leave smallmolecules such as vitamins and flavour componentsunaffected (Linton and Patterson 2000).Due to the work of compression, HPP causes temper-atures to rise inside the HP vessel. This is known asadiabatic heating and should be given due considerationduring the preservation process. The value of the temper-ature increments in the food and pressure transmittingmedium will be different, as they depend on foodcomposition as well as processing temperature and pressureand the rate of pressurisation (Otero et al. 2007a). In foodsterilisation, adiabatic heating can be used advantageouslyto provide heating without the presence of sharp thermalgradients at the process boundaries (Toepfl et al. 2006).Knowledge of the engineering concepts of HPP has been broadened extensively in recent times. Therefore, relevant engineering principles that promote the capabilities of HPPare discussed in the following.The Mechanisms of Cellular InactivationThe effectiveness of a food preservation technique is primarily evaluated on the basis of its ability to eradicatethe pathogenic microorganisms that are present. Cellular inactivation is closely associated with morphologicalchanges that occur within individual microbial cells during Table 1  Main suppliers of high pressure processing equipment and servicesCompany Company specialisation Services and/or products offered Pressure capacityof standardmachines (MPa)Resato Internationalhttp://www.resato.comThis company commercialiseslaboratory and industrial high pressure hydrostatic machinesThe company pressure shift freezing systems. Theyuse single shot or reciprocating intensifiers which aresuitable for one or multiple autoclave systemsUp to 1,400Avure Technologies Inc.,http://www.avure.comManufactures batch presses that  pasteurize prepared ready-to-eat foods, e.g. packaged meatsHave unique pumping systems that enhance product throughput. Continuous systems are not currently being developed600Elmhurst Research, Inc.,http://www.elmhurstresearch.comDesigns and manufactures batch pressesThe company has developed a system whichincorporates patent pending vessel technology. Thesystem that was developed exclusively for the food processing industry from scratch689Engineered PressureSystems Inc., http://www.epsi-highpressure.comManufactures laboratory andindustrial high pressure equipment for many industriesManufacture hot, cold and warm isostatic presses 100  –  900Kobelco, laboratory andindustrial high pressure equipment for many industriesManufacture many hot and cold isostatic presses, wet and dry-bag processes98-686Mitsubishi HeavyIndustries, laboratory andindustrial high pressure equipment for many industriesManufacture isostatic pressing system with largeoperating temperature range as option686 NC Hyperbaric, http:// www.nchyperbaric.comEuropean leader in manufacture of industrial HPP equipment Designed a system to work with different volumes,guaranteeing the necessary versatility to process awide range of products of different sizes and shapes600Stansted Fluid Power LTD. Offer a full range of advanced, high pressure equipment for research anddevelopment applicationsSingle and multiple vessels with temperature controlfrom  − 20 °C to +150 °C. Multiple Telemetry optionand variable pressurisation times from 2sUp to 1,400Uhde Hockdrucktechnik,http://www.uhde-hpt.comUhde develop and build high pressure processes for industry andresearch purposesHelp in the development of plant processes frominitial testing to full scale application700Food Bioprocess Technol (2008) 1:2  –  34 5
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