New Methods in Food Processing

PUBLISHED WORKS GUT HEALTH

New Methods in Food Processing

Finn Holm FoodGroup Denmark - Denmark (November 2001)

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GM FOODS Finn Holm FoodGroup Denmark - Denmark (June 2002)

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MYCOTOXINS Jean-François Quillien Institut National de la Recherche Agronomique - France (October 2002)

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FOOD QUALITY SENSORS Finn Holm FoodGroup Denmark - Denmark (January 2003)

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NEW FUNCTIONAL FOOD INGREDIENTS CARDIOVASCULAR HEALTH Finn Holm FoodGroup Denmark - Denmark (August 2003)

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NEW FUNCTIONAL FOOD INGREDIENTS CANCERS AND OXIDATIVE DEGRADATIONS Finn Holm FoodGroup Denmark - Denmark (October 2003)

D. Behsnilian, M. Regier, M. Stahl BFE - Federal Research Centre for Nutrition Germany

Project n° QLK1-CT - 2000 - 00040 N° ISBN : 2-7380-1137-3 November 2003

SMEs N° 7

Flair-Flow 4 is funded by the European Commission within the 5th Framework Programme under the Quality of Life and Management of Living Resources, Key Action 1. FlairFlow 4 is a network that disseminates food research results in 24 European countries. The two objectives of Flair-Flow 4 National Network Leader

This document is a Flair-Flow 4 synthesis report. It is one of a serie of biannual publications targeted to three categories of end-users : SME, Consumers and Health Professionals.

1 – To disseminate results from European Union sponsored food research programmes. The European Commission finances about a hundred food research projects each year, on topics such as consumer needs and attitudes, nutrition, food safety, technology... In Flair-Flow 4 we tailor the scientific information to three categories of end users (Small and Medium Enterprises - Consumer Groups - Health Professionals) and disseminate these documents to end-users through our European network. 2 – To open a dialogue between scientists and each category of end-users. Each national Flair-Flow 4 network leader organises in their country debates in the form of panels. The topics for debates are chosen by the end-users themselves. The methodology used is the same in each country and for each type of end-users but the topics may be different.

Institut National de la Recherche Agronomique 147, rue de l’Université 75338 PARIS cedex 07 - France Coordinator : Jean-François Quillien [email protected]

www.flair-flow.com

NEW METHODS IN FOOD PROCESSING

D. Behsnilian, M. Regier, M. Stahl BFE - Federal Research Centre for Nutrition Germany

The opinions contained in this document are the sole responsibility of the authors and do not necessarily reflect the official opinion of th European Commission

SMEs n° 7

Contents Introduction

page 4

1- High pressure treatment 1.1 Why treat with high pressure? 1.2 How does the process function? 1.3 Products and legal regulations? 1.4 What effects does the process have on the quality of the product? 1.5 EU-financed research projects 1.6 Further literature 1.7 Project literature

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2- Osmotic treatment

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3- Electrical pulse methods (high voltage impulses) 3.1 Why treat with high voltage impulses? 3.2 How does the process function? 3.3 Products and legal regulations? 3.4 Overview of EU-financed projects 3.5 Further literature

33 33 33 35 37 38

4- New high (radio) frequency and microwave methods 4.1 Standard method for determining the uniformity of heating in microwave ovens 4.2 Optimum control of microwave combination ovens for heating foods 4.3 Electromagnetic heating processes for food production 4.4 Radio frequency heating technology for minimally-processed fish products 4.5 Further literature

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44 45 46 48

Illustration front page published by permission from BFE

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Introduction Food processing means the conversion (refinement) of biological raw materials into consumer foods and maintenance of their keeping quality during transport, trade and storage. Processing aims are therefore essentially concentrated on adapting products to the requirements of nutritional physiology. This can mean eliminating substances foreign to foods, improving raw material by concentrating desirable or depleting undesirable constituents and, in particular, the mildest possible processing to maintain the original properties of the food to the greatest possible degree, or even improve them. Within this framework, avoiding or minimising microbiological contamination as well as limiting food quality losses due to enzymatic reactions by thermal processing, e.g. by blanching, pasteurisation or sterilisation, play major roles in food production. In addition to conventional methods of heating food by contact, modern methods of food processing are increasingly being applied. Some of these new processing techniques were initially used in other industrial fields, e.g. in finishing of surfaces (plasma), for production of diamonds, compressed powders etc. (high pressure technique) or in radar technology (microwaves). Some of them however have been developed specifically for use in the food industry (e.g. osmotic treatment).

Examples of new food processing methods are heating by non-ionising radiation (infrared, radio frequency, microwave) or by ohmic methods, irradiation with ionising radiation, osmotic treatment, high pressure treatment, treatment with high electrical pulses or plasma sterilisation of packaging materials. These methods are becoming more and more important since, by applying them alone or in combination, it is possible to attain novel product properties and quality levels. This is also reflected in the sharply growing number of EU-financed projects concerned with modern methods of food processing and technology. A selection of EU-financed research projects is summarised in the following chapters. Further information can be obtained from the particular project co-ordinators named. These projects deal with the following new methods: 1. 2. 3. 4.

High pressure treatment Osmotic treatment Electrical pulse methods High frequency and microwave treatment

Reasons for the development and application of modern conventional and new food processing methods are: to enhance the nutritional, microbiological and sensory quality; to improve the processing characteristics of raw materials and semi-finished products; to increase product diversity and to augment the intrinsic value of ready to eat foods. Furthermore, economic and environmental criteria, which take into account consumer protection and meet consumer requirements, contribute to the further development of food processing methods. 4

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1- High pressure treatment 1.1 Why treat with high pressure? High pressure pasteurisation is a relatively new physical method of preserving foodstuffs. The generic terms «high pressure treatment», «ultra-high pressure treatment», «UHP» and «high pressure processing (HPP)» are often also used. The aim of high pressure treatment is to inactivate undesirable microorganisms and enzymes with this non-thermal («cold») method without having to accept the losses in quality which occur when heat is applied. The sensory and nutritional quality is said to be maintained particularly well in high pressure pasteurised products compared with untreated products. The use of sufficiently high pressures transferred by liquids (hydrostatic) has been the subject of intensive investigation for some years as a gentle alternative to preservation of foodstuffs by means of heat. Such pasteurised foodstuffs have already been introduced on to the Japanese market. In contrast to preserving by heating, low molecular weight compounds such as vitamins, essential amino acids, flavours, colour and structure are not, as a rule, affected by high pressure treatment. Fruit juices sterilised by high pressure can, e.g., retain their natural flavour.. Heat-sensitive, antimutagenic and therefore health-promoting substances in fruit and vegetables are also largely retained. In addition to prolonging the shelf life by inactivation of microorganisms and enzymes while at the same time retaining natural freshness, other properties of foodstuffs can also be modified by the effect of the pressure. By pressure, e.g., starch gels become more stable, muscle flesh becomes more tender and chocolate becomes creamier. Innovative products can be developed with properties that cannot be achieved by other means. In view of the comparatively high costs of constructing and maintaining 6

appropriate high pressure plants, however, the quality of foodstuffs treated under high pressure would have to be very convincing so that the consumer accepts the resultant higher prices. 1.2 How does the process function? The first plant for high pressure treatment of foodstuffs was constructed by Hite in 1889. Further research work followed in the 1920s and 1960s. However, only after technical advances in materials technology and the founding of a research consortium of 21 Japanese companies in 1989 with the aim of commercial utilisation of UHP technology did the high pressure research on foodstuffs and its use receive impetus. In the 1990s, various foodstuffs treated under high pressure appeared on the Japanese market. With this method, the chemical equilibrium and the rate of reaction are influenced by the increase in pressure. Generally, a process, whether a chemical reaction or a phase transition, will proceed preferentially under pressure if the end product occupies a smaller volume than the starting substance did (LeChatelier-Braun principle, «escape from force»). The action of pressure thus favours all processes that are associated with a reduction in volume. Phase transitions or chemical reactions in which the end product has a smaller volume than the starting substance therefore proceed preferentially. The individual constituents of a foodstuff react differently to exposure to high pressure. Since covalent bonds are retained under pressure, smaller molecules (e.g. vitamins, flavour substances) are less sensitive to pressure than larger molecules (e.g. proteins), whose spatial structure is caused by weaker types of bonds. For pressure treatment in the «wet bag» process, solid foodstuffs are packed in flexible, watertight and pressure-resistant containers (e.g. in welded films) and are introduced into a pressure container. This also contains water, which serves as the medium for transfer of pressure. Hydrostatic pressure is then applied to a foodstuff. After the foodstuffs (without inclusions of gas) have been introduced into the water-filled cylinder (Figure 1 – A), the pressure is increased with a tightly sealing

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plunger (Figure 1 – B) so that the pressure (up to 700 MPa) can be transferred in this way. The hydraulic liquid returns to the collecting tank (Figure 1 – C) via a throttle. During high pressure treatment, foodstuffs are exposed to a pressure of between 100 up to 1,000 MPa (1,000 to 10,000 bar). Liquids which are compatible with the materials of the high pressure plant and the packaging of the product are used as the pressure transfer medium. The pressure transfer medium should have the lowest possible compressibility so that the pressure can build up rapidly. Water containing anticorrosives (sodium benzoate) and lubricants are usually used as additives. Figure 1: Outline principles of a plant for high pressure preservation

The heating accompanying the compression increases the temperature only by about 3ºC at 100 MPa or 25º at 800 MPa. If required, the pressure chamber can also be temperature-controlled via a heat exchanger. At the end of the action time (usually 5-20 minutes), the chamber is released again to ambient pressure and the foodstuff is removed (batch process).

England milk, in Spain boiled ham). In addition, meat, fish, milk and eggs can also be treated by the high pressure technique. With the ruling of the European Commission of 23rd May 2001, approval was granted to bring fruit preparations pasteurised by high pressure on to the market in the EU as a novel foodstuff ingredient in the context of the Novel Food Regulation. The fruit preparations and any foodstuff in which these are used must be labelled «high pressure pasteurised». Foodstuffs, which have been subjected to treatment with pressures above 150 MPa, can be regarded as novel in the context of the Novel Food Regulation (EC No. 258/97). Novel Foods here are, amongst others, foods which have been processed by a hitherto uncommon method that results in significant changes in the composition and structure of the end product, which in turn has an effect on the nutritional value, the digestibility or the content of undesirable constituents. 1.4 What effects does the process have on the quality of the product? 1.4.1 Constituents

1.3 Products and legal regulations?

Under high pressure, the viscosity of water and aqueous solutions increases and the pH decreases. Salts and acids dissociate and as the pressure increases, they are increasingly present in the form of individual ions.

Products treated under high pressure, such as jams, fruit jellies, rice meals and mandarin and grapefruit juice, have been available on the market in Japan since 1990. The products are on average about 2.5 times more expensive than those produced by conventional methods. In the USA, avocado purée preserved using high pressure is available on the market. Before the Novel Food Regulation came into force, products pasteurised by high pressure were also already brought to market in various countries in Europe (in France orange and grapefruit juice, in

High pressure influences the bonds which stabilise the spatial structure of proteins. Depending on the pressure level, the protein structures are modified reversibly or irreversibly i.e. denatured. Influencing factors are the pressure, the temperature, the protein structure, the pH and the composition of the solvent. Hinrichs gives formal kinetic data on the pressure- and temperature-induced denaturation of various proteins. In the case of enzymes, which of course are also proteins, the change in structure (denaturing) can cause the properties of the enzymes to be

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affected. The activity of the enzyme can be either decreased or increased. However, proteins can also be modified in a targeted way by high pressure treatment. For example, the formation of protein gels, which are very smooth and elastic, is made possible by structural changes. The use of such gels for new products, e.g. in the desserts sector, is conceivable. The fact that muscle flesh and fish become tender by high pressure treatment can also be utilised in foodstuff technology. The action of high pressure can modify behaviour during melting and crystallisation of fats. Fats crystallise out under the action of pressure because the specific volume of crystallised fat is smaller than that of liquid fat. This also occurs in emulsion drops, the emulsion remaining stable. High pressure treatment also influences the chemical composition of fats. The extent to which fat decay is delayed or promoted by oxidation depends on the composition of the foodstuffs and the treatment conditions. The molecular structure of simple carbohydrates (sugars) is not modified by high pressure treatment. However, it is possible that the properties of carbohydrates are affected, e.g. their ability to bond water. Starch in an aqueous environment can be made into a paste under pressure. Starch gelled under pressure shows a lower degree of retrogradation during storage compared with one gelled under heat and its digestibility is additionally improved. Such gels can be used as substitutes for fats. The enzymatic breakdown of carbohydrates can proceed differently in foodstuffs treated under high pressure to that in untreated foodstuffs. Non-enzymatic browning reactions (Maillard reactions) such as often occur during pasteurisation by heat are suppressed by a high pressure treatment, so that fewer colouring and flavouring substances are formed. Studies show that vitamins A, B1, B2, B6 and C are stable over short exposure times. The vitamin C content e.g. in orange juice treated under high pressure is approximately the same as that in untreated juice. The water-soluble antioxidative potential of orange juice, for which Lascorbic acid and phenolic compounds are mainly responsible, is also

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largely retained after high pressure treatment. The carotenoid content of an orange-carrot-lemon nectar is affected only little, if at all, by high pressure treatment. Colourings and flavour substances are likewise stable given suitable process conditions. Flavouring substances are also retained virtually unchanged during the high pressure treatment. 1.4.2 Microorganisms Since enzymes and proteins are also important constituents of microorganisms, their modification can also have an effect here. Microorganisms have different sensitivities to pressure. While yeasts, moulds and vegetative microorganisms can be inactivated at a relatively low pressure, this only happens in some viruses and bacterial spores when they are exposed to very high pressures or are also additionally heat-treated. Spores can be made to germinate under low pressure, in order to kill the germinated spores under a higher pressure. Complete destruction of Bacillus subtilis, both of the vegetative organisms and of the spores, has been achieved at temperatures of about 70ºC and pressures of about 200 MPa. 1.4.3 Texture This method is suitable not only for prolonging the life of the foodstuff by reducing the microbial contamination and enzyme activity; it can also be applied to raw materials and ingredients to influence their functional properties. New process strategies e.g. in thawing and freezing and new innovative products can moreover be developed, since by protein denaturation, gel formation of carbohydrates and modification of activation volumes, modification in structure and texture and inactivation of enzymes can occur. Using pressure treatment, thawing and freezing can be carried out under milder conditions and fat crystallisation in chocolate and milk fat can be accelerated. The gelatinous consistency and viscosity of fermented yoghurt is likewise increased by hydrostatic pressure

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treatment. There is, furthermore, the possibility of producing novel products with a base matrix established by high pressure treatment of the foodstuff. Examples are pastes or gels based on egg, fish, meat and milk protein. 1.5 EU-financed research projects FAIR-CT96-1113 ”High pressure treatment of liquid foods and derived products” Contact: Jo Belsten, Press officer, Institute of Food Research, Colney, Norwich, NR4 7UA, UK; Tel: 01603 255218, Fax: 01603 255168, E-mail: [email protected] FAIR-CT96-1175 “Combined high pressure thermal treatment of foods: a kinetic approach to safety and quality evaluation” Contact: Prof. Dr. Ir. M. Hendrickx, Dept. of Food and Microbial Technology, Katholieke Universiteit Leuven, Kasteelpark Arenberg 22, B-3001 Heverlee, BELGIUM Tel: +32-16-321572, Fax: +32-16-321960. E-mail: [email protected]

QLK1-CT-2002-02230 (SAFE-ICE) "Low temperature-pressure processing of food: Safety and quality aspects, process parameters and consumer acceptance" Contact: Ulrike Schmidtberg, TU Berlin, 10623 Berlin, GERMANY. Tel: +49/30/314-22 365; Fax: +49/30/314-21 689; E-mail: [email protected] AIR 10296 "High hydrostatic pressure treatment, its impact on spoilage organisms, biopolymer activity, functionality and nutrient composition of food systems." Contact: Prof. Dr. Knorr Dietrich, TU-Berlin, Insitut für Lebensmitteltechnologie, 14195 Berlin, GERMANY. Tel:+49-30-31471250; Fax:+49-30-8327663; E-mail: [email protected]

ICA1-CT-2000-70005 "High pressure: a competitive method for the advancement of multidisciplinary research and industrial applications". Contact: Trezeciakowski, Witold, High Pressure Research Centre-Polish Academy of Sciences, 28-37 Sokolowska 29-37, P.O. Box 52, 01 142 Warszawa, POLAND. QLK1-CT-2001-42274 "Minimal and safe processing of foods by continuous high pressure homogenisation" Contact: Camps, Pere; XUCLA-Camps S.A., Avenue Europa 12, 17800 Olot, Girona, SPAIN.

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1.5.1 Selection from the research sector (overview) FAIR

Lipolysis, Goats' cheese, High pressure treatment

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1113 Changes in textural, microstructural and colour characteristics during ripening of cheeses from raw, pasteurised or high-pressure-treated goats' milk.

Texture, Microstructure, Colour, Goats' milk cheese, High pressure treatment

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1113 Different action patterns for apple pectin methylesterase at pH 7.0 and 4.5.

Apple, Pectin methylesterase, Action patterns, Interchain and intrachain distributions.

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1113 The effect of exposure to a pressure of 50 MPa on Cheddar cheese ripening.

High pressure, Cheddar, Cheese, Ripening.

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Key words

See project literature no.

1113 Emerging technologies: Chemical aspects

Non-thermal, Foodstuffs processing, Liquid high pressure; High voltage field.

1

1175 Changes in functional properties of vegetables induced by high pressure treatment

High pressure, Vegetables, Functional; Extractability, Availability.

2

1113 High pressure processing of dairy foods

Cheddar cheese, Ripening, 3 Inactivation, Costs, Bacteriocins. High pressure, Ultra-high pressure, Antimutagenic, Antioxidative, Fruit, Vegetables.

4

1175 Influence of activation and germination on high pressure inactivation of ascospores of the mould Eurotium repens.

Activation, Ascospores, Dormant spores, Eurotium repens, Heat activation, Moulds, Germination, Pressure activation.

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1113 Influence of ultra-high pressure processing on fruits and vegetable products

High pressure, Gouda, Cheese, Rheology

5

1175 Kinetics studies on high-pressure inactivation of Bacillus stearothermophilus spores suspended in food matrices

Bacillus stearothermophilus, Spores, Pressure, Temperature.

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1113 Rheological properties of high pressure-treated Gouda cheese 1113 Proteolysis of highpressure-treated Gouda cheese

High pressure, Gouda cheese, Ripening.

6

1175 Effect of high pressure on the physical properties of barley starch.

High pressure, Barley, Starch, Gelling, Rheology, Microscopy, TLC, Retrogradation

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1113 Transport of sodium chloride and water in Gouda cheese as affected by high pressure brining

High pressure, Alkaline solution, 7 Gouda, Cheese.

1175 Effect of combined application of high pressure treatment and modified atmosphere on the shelf-life of fresh Atlantic salmon.

Salmon, Decay, High Pressure, Modified atmosphere, Hurdle technology.

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1113 Proteolysis in goats' cheese made from raw, pasteurised or pressuretreated milk.

High pressure, Goats' cheese, Proteolysis.

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High pressure treatment, Model development, Heat transfer, Process uniformity.

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1113 The effects of high pressure treatment on the functional and rheological properties of Mozzarella cheese.

High pressure, Mozzarella, Cheese, Functionality

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11175 A modelling approach for evaluating process uniformity during batch high hydrostatic pressure processing: combination of a numerical heat transfer model and enzyme inactivation kinetics. 11175 Two-dimensional Fourier-transformation infrared correlation spectroscopy study of the high-pressure tuning of proteins

H/D exchange, Proteins, FTIR correlation, Spectroscopy.

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1113 Effects of high pressure treatment on viability and autolysis of starter bacteria and proteolysis in Cheddar cheese

High pressure, Cheddar, Cheese, Autolysis, Proteolysis, Lactococcus lactis.

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11175 Evaluation and modelling of rheological properties of high pressure treated waxy maize starch dispersions.

Modelling, Rheology, Maize, Starch.

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1113 Effect of high pressure processing on physico-chemical characteristics of fresh goats' milk cheese (Mató).

High pressure processing, Fresh cheese, State, Structure.

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11175 In situ observation of pressure-induced gelation of starches studied with FTIR in the diamond anvil cell

Starch, Gelling, High Pressure, Infra-red spectroscopy.

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Title

1113 Lipolysis in cheese made from raw, pasteurised or high-pressure-treated goats' milk.

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1.6 Further literature J.C. Cheftel High Pressure and Biotechnology, 224, 1992, 195-209. R. Hayashi (ed.) Use of High Pressure in Food. San-Ei Publ. Co., Kyoto, 1989. W. Buchheim, D. Prokopek Deutsche Milchwirtschaft, 43, 1992, 1374-1378. D. Knorr New Methods of Food Preservation (ed. G.W. Gould), 159-175, Blackie Academic & Prof., London, 1995. B. Tauscher Pasteurisieren von Lebensmitteln mit hydrostatischem Hochdruck, AID Verbraucherdienst [Pasteurisation of Foodstuffs with Hydrostatic High Pressure, AID Cunsumer Service, Zeitschrift für Fach-, Lehr- und Beratungskräfte im Bereich Ernährung, 40, 1995, 3, 51-57. P. Butz, B. Tauscher Internat. Rev. Food Sci. Technol. 2002, 1, 84-87.

K.J. Morris Isostatic Pressing Technology (ed. P.J. James), 92-115, Applied Science Pul., London, 1983. V. Heinz, D. Knorr, O. Schlüter, O. Spektrum der Wissenschaft, 1989, 11,132-136. J.C. Cheftel High Pressure Food Science, Bioscience and Chemistry, (ed. N.S. Isaacs),506-507, The Royal Society of Chemistry, Cambridge, UK, 1998. P. Rovere Ultra High Pressure Treatment of Foods (ed. M.E.G. Hendrickx, D. Knorr), 251-268, Kluwer Academic / Plenum Publishers, New York, 2002. EU Ruling of the Commission of 23rd May 2001 on the approval of marketing of high pressure-pasteurised fruit preparations in accordance with Regulation (EC) No. 258/97 of the European Parliament and Council, OJ No. L 151 of 07.06.2001, 42–43.

B.H. Hite West Virginia Agrucultural Experiment Station, Morgantown, Bulletin, 58, 1899, 15-35.

M. Michel, K. Autio Ultra High Pressure Treatment of Foods (ed. M.E.G. Hendrickx, D. Knorr), 189-214, Kluwer Academic / Plenum Publishers, New York, 2002.

A.J.H. Sale, G.W. Gould, W.A. Hamilton, J. Gen Microbiology, 60, 1970, 323-334.

C. Balny, P. Masson Food Rev. Int., 1993, 9, 611-628.

M. Pfister, L.I. Dehne Deutsche Lebensmittel-Rundschau, 97, 2001, 7, 257–268.

P. Masson High Pressure and Biotechnology (ed. C. Balny, R. Hayashi, K. Heremans, P. Masson), 89-99, J. Libbey, Eurotext Ltd., 1992.

P.J. James Isostatic Pressing Technology (ed. P.J. James), 1-25, Applied Science Pul., London, 1983. 16

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A. Fernández García, P. Butz, B. Tauscher Mechanism-based irreversible inactivation of horseradish peroxidase at 500 MPa, Biotechnology Progress 18, 2002, 1076-1081.

N.S. Isaacs, M. Coulson High Pressure Bioscience and Biotechnology (ed. R. Hayashi, C. Balny),479-484, Elsevier, Amsterdam, 1996.

L. Ludikhuyze, A. Van Loey, Indrawati, S. Deny, M.E.G. Hendrickx Ultra High Pressure Treatment of Foods (ed. M.E.G. Hendrickx, D. Knorr), 115-166, Kluwer Academic / Plenum Publishers, New York, 2002.

A. Fernández García, P. Butz, A. Bognar, B. Tauscher Eur. Food Research Technology, 213, 2001, 290–296.

J.C. Cheftel, J. Culioli Meat Sci., 46, 1997, 211-236. M. Gudmundsson, H. Hafsteinsson Trends Food Sci. Technol. 12, 2001, 3-4, 122-128. D.A. Ledward Fresh novel foods by high pressure (ed. K. Autio), 165-176, VTT Symposium 186, Espoo, Finland, 1998. E. Dransfield Adv. Meat Res. 9, 1994, 289-315. W. Buchheim, E. Frede, M. Wolf, P. Baldenegger Advances in High Presure Bioscience and Biotechnology (ed. H. Ludwig), 153-156, Springer, Berlin, 1999. W. Buchheim, A.-M. El-Nour Fat. Sci. Technol. 94, 1992, 369-373. G. Donsi, G. Ferrari, M. de Matteo Ital. J. Food Sci., 1996, 2, 99-106. K. Autio, M. Stolt Fresh Novel Foods by High Pressure (ed. K. Autio), 61-67, Julkaisija Utgivare, Espoo, Finland, 1998.

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J.P. Smelt, J.C: Hellemons, M. Patterson Ultra High Pressure Treatment of Foods (ed. M.E.G. Hendrickx, D. Knorr), 55-76, Kluwer Academic / Plenum Publishers, New York, 2002. B. Rademacher Dissertation, TU München-Weihenstephan, 1999. V. Heinz Dissertation, Technical University, Berlin, 1997. S. Denys, O. Schlüter, M.E.G. Hendrickx, D. Knorr Ultra High Pressure Treatment of Foods (ed. M.E.G. Hendrickx, D. Knorr), 215-248, Kluwer Academic / Plenum Publishers, New York, 2002. D. Knorr, O. Schlüter, V. Heinz Food Techn. 52, 1998, 9, 42-45. W. Buchheim, E. Frede DMZ, 1996, 5, 228-237. J. Hinrichs, B. Fertsch Deutsche Milchwirtschaft, 20, 1999, 50, 875-878. P. Butz, B. Tauscher Emerging technologies: Chemical Aspects, Food Research International 35, 2002, 279–284.

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1.7 Project literature 1- P. Butz, B. Tauscher, Emerging technologies: Chemical Aspects, Food Research International 35, 2002, 279–284. 2- P. Butz, R. Edenharder, A. Fernández García, H. Fister, C. Merkel, B. Tauscher, Changes in functional properties of vegetables induced by high pressure treatment, Food Research International 35, 2002, 295–300.

8- A.J. Trujillo, M. Buffa, I. Casals, P. Fernández, b. Guamis, Proteolysis in goat cheese made from raw, pasteurized or pressuretreated milk, Innovative Food Science & Emerging Technologies 3, 2002, 309-319. 9- Ciara E. O´Reilly, Patrick M. Murphy, Alan L. Kelly, Timothy P. Guinee, Mark A.E. Auty, Thomas P. Beresford, The effect of high pressure treatment on the functional and rheological properties of Mozzarella cheese, Innovative Food Science & Emerging Technologies 3, 2002, 3-9.

3- W.J. Donelly, T. Beresford et al., High Pressure Processing of Dairy Foods, Dairy Products Research Center, Moorepark, Project Report DPRC No. 22, 1999.

10- Ciara E. O´Reilly, Paula M. O´Connor, Patrick M. Murphy, Alan L. Kelly, Thomas P. Beresford, Effect of high-pressure treatment on viability and autolysis of starter bacteria and proteolysis in Cheddar cheese, Innovative Food Science & Emerging Technologies 12, 2002, 915-922.

4- P. Butz, A. Fernández García, R. Lindauer, S. Dietrich, A. Bognár, B. Tauscher, Influence of ultra high pressure processing on fruit and vegetable products, Journal of Food Engineering 56, 2003, 233-236.

11- M. Capellas, M. Mor-Mur, e. Sendra, B. Guamis, Effect of high-pressure processing on physico-chemical characteristics of fresh goat´ milk chees (Mató), International Dairy Journal 11, 2001, 165-173.

5- Winy Messens, Davy Van de Walle, Juan Arevalo, Koen Dewettinck, André Huyghebaert, Rheological properties of high pressure-treated Gouda cheese, International Dairy Journal 10, 2000, 359-367.

12- Martín Buffa, Buenaventura Guamis, Marta Pavia, Antonio J. Trujillo, Lipolysis in cheese made from raw, pasteurized or high-pressuretreated goat´s milk, International Dairy Journal 11, 2001, 175-179.

6- Winy Messens, Juncal Estepar-García, Koen Dewettinck, André Huyghebaert, Proteolysis of high-pressure-teated Gouda cheese, International Dairy Journal 9, 1999, 775-782.

13- Martín Buffa, Antonio J. Trujillo, Marta Pavia, Buenaventura Guamis, Changes in textural, microstructural, and colour characteristics during ripening of cheeses made from raw, pasteurized or high-pressuretreated goats´milk, International Dairy Journal 11, 2001, 927-934.

7- Winy Messens, Koen Dewettinck, André Huyghebaert, Transport of sodium chloride and water in Gouda cheese as affected by high-pressure brining, International Dairy Journal 9, 1999, 569-576.

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14- Jean-Marc Denès, Alain Baron, Catherine M.G.C. Renard, Christophe Péan, Jean-François Drilleau, Different action patterns for apple pectin methylesterase at pH 7.0 and 4.5, Carbohydrate Research 327, 2000, 385-393. 21

15- Ciara E. O´Reilly, Paula M. O´Connor, Patrick M. Murphy, Alan L. Kelly, Thomas P. Beresford, The effect of exposure to pressure of 50 MPa on Cheddar cheese ripening, Innovative Food Science & Emerging Technologies 1, 2000, 109-117.

22- M. Stolt, N.G. Stoforos, P.S. Taoukis, K. Autio, Evaluation and modelling of rheological properties of high pressure treated waxy maize starch dispersions, Journal of Food engineering 40, 1999, 293-298.

16- R. Eicher, H. Ludwig, Influence of activation and germination on high pressure inactivation of ascospores of the mould Eurotium repens, Comparative Biochemistry and Physiology Part A 131, 2002, 595–604.

23- P. Rubens, J. Snauwaert, K. Heremans, R. Stute, In situ observation of pressure-induced gelation of starches studied with FTIR in the diamond anvil cell, Carbohydrate Polymers, 1999, 231-235.

17- E. Ananta, V. Heinz, O. Schlüter, D. Knorr, Kinetic studies on high-pressure inactivation of Bacillus stearothermophilus spores suspended in food matrices, Innovative Food Science & Engineering Technologies 2, 2001, 261-272. 18- M. Stolt, S. Oinonen, K. Autio, Effect of high pressure on the physical properties of barley starch, Innovative Food Science & Emerging Technologies 1, 2001, 167-175. 19- A. Amanatidou, O. Schlüter, K. Lemkau, L.G.M. Gorris, E.J. Smid, D. Knorr, Effect of combined application of high pressure treatment and modified atmospheres on the shelf life of fresh Atlantic salmon, Innovative Food Science & Emerging Technologies 1, 2000, 87-98. 20- S. Denys, A.M. Van Loey, M.E. Hendrickx, A modeling approach for evaluating process uniformity during batch high hydrostatic pressure processing: combination of a numerical heat transfer model and enzyme inactivation kinetics, Innovative Food Science & Emerging Technologies 1, 2000, 5-19. 21- L. Smeller, P. Rubens, J. Frank, J. Fidy, K. Heremans, Two-dimensional Fourier-transformation infrared correlation spectroscopy study of the high-pressure tuning of proteins, Vobrational Spectroscopy 22, 2000, 119-125.

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2- Osmotic treatment Osmosis Osmotic treatment has been used for preserving foodstuffs in a more or less empirical manner for a long time. Candying of fruit and salting of vegetables, meat and fish are examples of traditional preserving processes based on the principle of osmosis. Removal of water and impregnation of the food material with sugar or salt are of major importance for the long term preservation of the products. Nowadays osmotic treatment is no longer used merely as a method for preserving foodstuffs, but as a pre-treatment to drying or freezing. The aim is to modify the chemical (composition) and/or physical (porosity, density) properties of the food material in a controlled manner. For osmotic treatment, the food material (plant or animal tissue) is introduced into an aqueous solution of increased osmotic pressure, i.e. with a relatively high concentration of dissolved substances. Because of the existence of semi-permeable cell membranes in the tissue and the different concentrations of dissolved substances in the cell fluid and in the solution, the following processes are triggered: - Water diffuses out of the cells (tissue) into the solution, and so is removed from the tissue. - Due to the removal of water, the cells shrink and the intercellular spaces become larger and are filled with the solution. An uptake of dissolved substances by the tissue takes place. The process can be carried out in various temperature ranges depending on subsequent processing steps (see Table 1), the product is not additionally exposed to heat. Since usually only water activity values above aw = 0.9 can be attained in osmotic solutions suitable for food, it is not possible to preserve food material in the long term by osmotic treatment alone.

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Osmosis is the diffusion of molecules or ions through a selective (semi-permeable) membrane from a place of higher concentration to a place of lower concentration until the concentration on both sides is equal. The selectivity can be achieved, for example, by the pore/particle size ratio or specific interactions. Osmosis is the diffusion of water molecules through a membrane, as shown by the example of a sugar solution in the figure. Since the membrane is semi-permeable, the small water molecules can migrate through in both directions, but the large sugar molecules cannot penetrate through the membrane into the water (Figure a). A one-sided migration of the water molecules into the sugar solution can be observed, so that the level in this chamber rises (Figure b). Sugar Water

Semi-permeable membrane

25

Process parameter

Cases

Range

Temperature

standard treatment and blanching treatment and cooling standard POD / PVOD

20 °C – 50 °C 60 °C - 90 °C 10 °C atmospheric vacuum / pulsed vacuum high pressure 30 – 240 min up to 24 h

Pressure

Treatment time

standard

Table 1: Typical process parameters in osmotic treatment.

Products treated by osmosis are particularly suitable for further processing, e.g. for hot air drying or for freezing; in both cases the process costs are considerably lower than those for processing fresh material. When refrigerated, the products can be stored longer than fresh products. Fruit and vegetables exposed to a mild osmotic treatment can be eaten or processed in the same way as fresh fruit and vegetables. Such products can be added to yoghurt or other dairy products, fresh salads or uncooked meals. Partial removal of water by osmotic treatment in concentrated sugar solutions has also been proposed for optimising the quality of frozen or dried fruit.

Mono-, di- and polysaccharides and inorganic salts are chiefly employed as osmotically-active substances (Table 2). When choosing these substances, not only their osmotic action is of importance, but also their influence on the sensory properties of the product and their suitability as foodstuff additives, since the solutes are taken up by the tissue. By osmotic treatment, a great part of the initial water can be removed without exposure to heat. A low exposure to heat is generally associated to a low loss of colour and flavour components. At the same time as water is removed, it is also possible to introduce into the foodstuff protective substances in a controlled way, such as e.g. sucrose. Table 3 shows a summary of some advantageous properties of products which have been produced by osmotic treatment.

Agent

Concentration- %(w/w)

aw

Sucrose Glucose Maize syrup Glycerol Sodium chloride

60 50 60 90 10

0.89 0.95 0.93 0.57 0.93

-

70 55 70 96 22

-

0.84 0.93 0.89 0.52 0.82

Table 2: Examples of solutions for osmotic treatment and water activity values.

Comprehensive information currently exists on the use of osmotic treatment as a precursor to the following processes: air drying; vacuum drying; microwave drying; freeze-drying; sun drying; pasteurisation; production of preserves; freezing. The use of osmotic treatment has been studied mainly on fruit and vegetables, but also on fish and meat. The effectiveness of various solutes in binary - or multi-component aqueous solutions and the influence of temperature, concentration of the solution and contact time on the water transport have been intensively investigated.

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27

Process

Product

Advantages of an osmotic treatment Air drying kiwi, cherry, improved texture, strawberry, apple, colour and flavour retention carrot Microwave-vacuum apple low shrinkage, increased drying porosity, better rehydration Freeze-drying blueberry better texture and better flavour «Dehydro-freezing»: apricot, peach as an intermediate (for yoghurt): drying + freezing improved texture, prevents whey separation Freezing peas, strawberries better colour and texture; less «drip loss» Production of preserves peach improved texture Table 3: Advantages of an osmotic treatment as a precursor to conventional production processes.

The energy consumption for the removal of water and the process costs are very low compared with air drying. The spent solution is only rarely sold together with the product after osmotic treatment, contrary to what occurs in the production of preserves. However, the economic efficiency of the process is closely-linked to the recycling, re-use or further use, of the solution. During the treatment, the solution is diluted by the water removed from the product and also by the impregnation of the product. Furthermore, some soluble constituents of the food material, e.g. fruit acids or soluble proteins, are leached out and, as a consequence of slight mechanical damage, small pieces of the foods can also remain in the solution. Reuse (in the same process or in other processes) or disposal of the solution must therefore be optimised specifically for each application. The process was traditionally called «osmotic drying». Other common names are: «dewatering impregnation soaking (DIS)» and vacuum infusion (for treatment under vacuum or with a vacuum pulse).

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Water content (WC) = 80-90% Osmotic agent Fruit, vegetables, fish, meat

concentrated solution

Osmosis treatment

Concentrate

WC = 40% Treated product

Drying

Dilute solution

H2O

Freezing

Figure 1: Osmotic treatment as a component step of the process chain.

In the context of the project FAIR-96-1118 [1], which has already ended, the partners were concerned with three main fields of this technology application: 1.development of mathematical models of the treatment; 2.optimisation of the combined processes: Osmotic treatment + further processing; 3.management of the dilute solutions under economically favourable and environmentally-friendly conditions. The treatment of fruit, vegetables, fish and meat under various temperature and pressure conditions was investigated; both simple empirical and very complex mathematical models – which consider the microscopic properties of the tissue – were drafted and checked; new and valuable knowledge was obtained in the recycling of the solution. The books listed under «Further literature» at the end of this section summarise a great part of the results of FAIR-96-1118. 29

In the context of FAIR-98-3814 [3], the suitability and profitability of the vacuum infusion technique for processing fruit and vegetables was demonstrated. During the treatment, some of the gas enclosed in the plant tissue is removed (vacuum, 1 – 2 minutes under 0.1 – 0.2 bar) and replaced by the infusion or impregnation solution, which contains hydrocolloids (e.g. pectins, alginate or gelatin), fruit acids (e.g. ascorbic, citric or malic acid), calcium and sugar. By this treatment, some quality parameters, e.g. texture and appearance, are maintained to the optimum after further processing steps. Apples, peaches, strawberries, pears, mushrooms, cucumbers, pumpkins and other plant material were tested in the course of the project. The results showed that an increased firmness and reduced drip loss were achieved in thawed or pasteurised berries and fruit (e.g. for yoghurt, jams or confectionery fillings). The legal situation is still to be clarified in respect of the novel food regulation. Since vacuum infusion is considered as a new technology, approval for its products on the market has to be obtained. Osmotic treatment is also one of the favoured areas in co-operation projects with non-EU countries. The main goal of the Combidry project [4] is to gain the necessary scientific knowledge to optimise the application of osmotic treatment as a precursor to microwave drying of fruit.

EU-financed research projects 1- Osmotic Improvement of overall food quality by application of osmotic treatments in conventional and new processes (FAIR-96-1118) Project Coordinator: Prof. Dr.-Ing. Walter E.L. Spieß Federal Research Centre for Nutrition, Institute of Process Engineering Haid-und-Neu-Straße 9, 76131 Karlsruhe, GERMANY E-mail: [email protected] URL: www.bfa-ernaehrung.de/Bfe-Englisch/intern.htm 2- Osmotic Dehydration of fruits and vegetables at high temperature CIPE-92-6012 Project Coordinator: Andrzej Lenart Dep. Food Engineering,Warsaw Agricultural University, ul. Nowoursynowska 166, Warsaw 02 - 766, POLAND Fax: +48 22 434 602 E-mail: [email protected] 3- Improvement of processed fruit and vegetable texture by using a new technology. «vacuum technology» FAIR-98-3814 Project Coordinator: Khue-Chung Chantelier TMI International S.A. (Technology Marketing Innovation) Le Britannia Bt. C, 20 Bd. Eugène Deruelle, 69432 Lyon Cedex 03, FRANCE Tel : + 33 4 78 69 53 41 E-mail: [email protected] 4- COMBIDRY New combined drying technologies for development of high quality shelf-stable fruit products. ICA4-2002-10034 (Programme INCO 2) Project Coordinator: Dr. Kaj Martensson Swedish institute for food research and biotechnology AB Frans Perssons Vaeg 6, P.O. Box 5401, 402 29 - Göteborg, SWEDEN Tel:+46 31 33 55 600;Fax:+46 31 83 37 82 E-mail: [email protected]

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Further literature

3- Electrical pulse methods (high voltage impulses)

Dalla Rosa, M.; Spieß, W.E.L. (2000) Industrial applications of osmotic dehydration/treatments of food. Forum, Udine ISBN 88-8420-010-5

3.1 Why treat with high voltage impulses?

Fito, P.; Chiralt, A.; Barat, J.M.; Spiess, W.E.L.; Behsnilian, D. (2001) Osmotic dehydration and vacuum impregnation. Applications in food industries. Technomics Publ. Co., Lancaster Journal of Food Engineering Special Issue «Osmotic Treatments» (2001) 49 2/3 75-270 Sereno, A. (1998) Osmotic treatments for the food industry. FEUP Ed., Porto ISBN 972-752-026-X

Pulsed electrical fields of high field strength (high electric field pulses: HELP) can kill pathogenic and other microorganisms in foodstuffs without adverse effects on their nutritional value or their sensory properties. This new food processing technique is a non-thermal «pasteurisation» method which complies with the concept of minimal processing (MP). This concept is based on the requirement of the consumer for fresh and at the same time safe foodstuffs without the use of traditional preservatives [1,2,3,4,5,6]. Many traditional thermal processes are therefore ruled out, while other processes such as short-term high temperature, aseptic and in vacuum processes can be called MP processes. Other examples of non-thermal MP processes for erecting effective hurdles against microbial growth are: high pressure processes, packaging under a modified atmosphere, irradiation, light pulses, natural preservatives and combinations and moderate heat treatments. 3.2 How does the process function? The use of high voltage impulses for perforation of cell membranes was described for the first time in 1962 [7]. Thanks to technological advances, especially in the development of treatment chambers which can be operated continuously and scaled up, the foodstuffs industry has been showing interest in the potential of this method since the 1990s. HELP is a non-thermal method which uses electrical pulses of high field strength to tear the membranes of chiefly vegetative (microbial) cells or to make these membranes irreversibly permeable in order to bring about cell death. For treatment with high voltage impulses (PEF treatment), the goods to be treated are exposed to electromagnetic impulses of high field strengths (0.5 – 100 kV/cm) within micro- to milliseconds in a treatment chamber (discharge zone between two electrodes) (Fig. 1).

32

33

Generator

Charging circuit

Capacitor C, Voltage U 0 Discharge circuit

Charging resistance

Connecting resistance Switch

Conductivity k Treatment - chamber

Fig. 1 Diagram of a plant for treatment of foodstuffs with high voltage impulses (from [12]).

To generate the impulses, a capacitor is charged up by a high voltage generator and discharged in very short rectangular or exponentiallyfalling pulses (duration: to ms, energy densities in the range of 101 – 104 J/kg). 1 – 200 pulses are usually released. The time between the pulses is significantly longer than the duration of the pulses. The treatment chamber is filled with the foodstuff (batch operation) or the foodstuff flows through it (continuously operating plant) [8,9]. A dielectric collapse with sparking can cause problems. This is promoted above all in dispersions (foams, suspensions) and at higher temperatures

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[10,11]. Liquid foodstuffs are therefore degassed before the treatment. The action of the PEF process is based on permeabilisation of cell walls: In a pulsed electrical field the critical transmembrane potential of approx. 0.7 – 2.2 V is exceeded within less than 1 ms after the high voltage impulse has been triggered [12,13]. This leads to a sudden collapse of the membrane and local changes to the structure of the cell membrane. Open pores are formed within nanoseconds and grow within milliseconds [14,15,16,17,18]. The remaining matrix remains relatively unaffected by this [19,20]. The method is therefore comparable to electroporation known in biomedicine and cell biology. The pores can also close again within seconds on the basis of endogenous cell repair mechanisms (reversible pore formation), depending on the process conditions [21,22]. If the pulse frequency is the optimum and the critical field strength (10 – 15 kV/cm, [23]) is exceeded however, the pore formation is irreversible and leads to cell death [21, 24]. In addition, it may also be found that sub-lethal damage to the cell membrane is caused by high voltage impulses of low energy, leading to an irreversible permeabilisation of the cell membranes only some hours after the PEF treatment. This opens up new possibilities for an even milder product treatment [25,26]. PEF treatment can therefore be used as an alternative, non-thermal method for inactivating various vegetative microorganisms. Although no thermal energy is introduced directly into the product, a moderate increase in temperature nevertheless occurs, depending on its specific thermal capacity [27,28]. 3.3 Products and legal regulations? In spite of many advantages for the product and energy efficiency, this process has not yet become well accepted in the rather conservative foodstuff market. Things are made more difficult by the fact that the new process is subject to approval in accordance with the Novel Food Regulation (EC No. 258/97).

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Uses so far are chiefly in the pasteurisation of liquid products, for example green pea soup, milk and yoghurt, orange and apple juice and egg yolk and liquid egg [29,30,31,32]. Promising scientific studies show the suitability of a PEF treatment for pre-treatment of various varieties of fruit and vegetable (carrots, potatoes, apples, grapes, blackcurrants, coconuts or beetroot) before juice production or osmotic or thermal drying [33,34]. A PEF plant for increasing the extraction rate of sugar beet juice has also been developed at the TU Berlin and at the Forschungszentrum Karlsruhe [35,36]. Promising tests at a sugar producer's premises have led to the construction of a pilot plant with a throughput of 2,000 t/d [37,38]. The microstructure and texture of meat and fish are modified by electroporation of the cell membranes. Partial discharge of collagen into the cell interstices occurs. The PEF process is therefore not suitable for preserving fresh meat and fish [39].

Foodstuff

Apple juice from concentrate

Fresh apple juice

Untreated Beaten eggs skimmed milk

Green peas

Max. field strength / (kV/cm)

50

50

40

35

35

Pulse duration / ms

2

2

2

2

2

Pulse count / -

10

16

20

10

32

Starting temperature / ºC

8.5 ± 1.5

8.5 ± 1.5

10.0 ± 1.5

8.5 ± 1.5

22.0 ± 2.0

Max product temperature / ºC

45 ± 5

45 ± 5

50 ± 4

45 ± 5

53 ± 2

Table 1: Examples of process parameters for pasteurisation of various products (from [40])

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3.4 Overview of EU-financed projects: FAIR CT97-3044 The HELP project has been concluded and the results are published in Trends in Food Science & Technology (2002), 12, no 3-4, p. 93-144. The most important findings are: • In contrast to vegetative cells, most foodstuffs enzymes are not affected by HELP, proteins are not denatured and emulsions are not changed; • HELP can be a quality-maintaining method of preserving liquid foodstuffs; • HELP can inactivate microorganisms, including in particular yeast fungi and also Gram-positive and –negative bacteria, while bacterial spores are more resistant; • HELP has a softening effect on the texture of raw fish and meat; • HELP can be used effectively to improve mass transfer in subsequent processes, such as drying, extraction and pressing. Information can be obtained from: Prof. Dietrich Knorr Head of Department of Food Biotechnology and Process Engineering Berlin University of Technology Koenigin-Luise-Str. 22 D - 14195 Berlin, GERMANY Tel: +49 30 31471250; fax: +49 30 8327663 E-mail: [email protected] URL: http://www.tu-berlin.de/~foodtech QLK1-CT-2000-40742 Industrial process of food preservation by pulsed electric fields. Information can be obtained from: Milly, Roger; Enertronic SA, 30 rue du Ruisseau, 38070 Grenoble, FRANCE.

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3.5 Further literature 1- G.V. Barbosa-Canovas, M.M. Gongora-Nieto, U.R. Pothakamury, E.G. Swanson, Preservation of Foods with Pulsed Electric Field, Academic Press, San Diego, London, Boston, 1999. 2- Q.H. Zhang, G.V. Barbosa-Canovas, B.G. Swanson, J. Food. Engin. 25, 1995, 261-281. 3- Q.H. Zhang, F.J. Chang, G.V. Barbosa-Canovas, B.G. Swanson, Lebensm.-Wiss. u. Technol. 27, 1994, 538-543. 4- A.H. Bushnell, J.E. Dunn, R.W. Clark US Patent 5,048,404, 1991. 5- B.-L. Qin, G.V. Barbosa-Canovas, B.G. Swanson, P.D. Pedrow, R.G. Olsen, IEEE Trans. Ind. Applic. 34, 1998, 43-50. 6- Y. Yin, Q.H. Zhang, S.K. Sastry US Patent 5,690,978, 1997 7- H. Doevenspeck, Arch. Lebensmittelhyg. 13, 1962, 3, 6-7. 8- Q.H. Zhang, G.V. Barbosa-Canovas, B.G. Swanson, J. Food. Engin. 25, 1995, 261-281. 9- R. Heiss, K. Eichner Haltbarmachen von Lebensmitteln [Preserving Foodstuffs], 4th ed., 308-310, Springer, Berlin Heidelberg, 2002. 10- H.G.L.Coster, U. Zimmermann, J. Membr. Biol. 22, 1975, 73-90.

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11- B.L. Qin, Q. Zhang, G.V. Barbosa-Canovas, B.G. Swanson, P.D. Pedrow, Trans ASAE 38, 1995, 2, 557-565. 12- B. Rademacher Dissertation, TU München-Weihenstephan, 1999. 13- A. Angersbach, V. Heinz, D. Knorr Innov. Food Sci. & Emerg. Technol. 1, 2000, 135-149. 14- B. Rademacher Dissertation, TU München-Weihenstephan, 1999. 15- V. Heinz, I. Alvarez, A. Angersbach, D. Knorr Trends Food Sci. Technol. 12, 2001, 103-111. 16- A. Angersbach, V. Heinz, D. Knorr Innov. Food Sci. & Emerg. Technol. 1, 2000, 135-149. 17- J. Teissie, N. Eynard, B. Gabriel, M.P. Rols Adv. Drug Delivery Rev. 35, 1999, 3-19. 18- B. Rademacher Dissertation, TU München-Weihenstephan, 1999. 19- D. Knorr, A. Angersbach Trends Food Sci. Technol. 9, 1998, 185-191. 20- L. Barsotti, J.C. Cheftel Food Rev. Internat. 15, 1999, 2, 181-213. 21- A. Angersbach, V. Heinz, D. Knorr Innov. Food Sci. & Emerg. Technol. 1, 2000, 135-149. 22- B. Mertens, D. Knorr Food Technology, 5, 1992, 124-133.

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23- R. Heiss, K. Eichner Haltbarmachen von Lebensmitteln [Preserving Foodstuffs], 4th ed., 308-310, Springer, Berlin Heidelberg, 2002. 24- W.A. Hamilton, A.J.H. Sale Biochimica et Biophyica Acta, 148, 1967, 789-800. 25- B. Rademacher Dissertation, TU München-Weihenstephan, 1999. 26- D. Knorr et al. Trends in Food, Food Science & Technology (2001), 12, 129-135 27- G.V. Barbosa-Canovas, M.M. Gongora-Nieto, U.R. Pothakamury, E.G. Swanson Preservation of Foods with Pulsed Electric Field, Academic Press, San Diego, London, Boston, 1999. 28- B.L. Qin, Q. Zhang, G.V. Barbosa-Canovas, B.G. Swanson, P.D. Pedrow Trans ASAE 38, 1995, 2, 557-565. 29- G.V. Barbosa-Canovas, M.M. Gongora-Nieto, U.R. Pothakamury, E.G. Swanson Preservation of Foods with Pulsed Electric Field, Academic Press, San Diego, London, Boston, 1999.

33- G. Donsi, G. Ferrari, M. de Matteo Ital. J. Food Sci., 1996, 2, 99-106. 34- B. Mertens, D. Knorr Food Technology, 5, 1992, 124-133. 35- M.N. Eshtiaghi, D. Knorr Internat Patent WO 99/64634, 1999. 36- M.N. Eshtiaghi, D. Knorr Food Eng. Packaging Technol. (LVT), 45, 2000, 23-27. 37- J. Hoffmann Press information from the FZK Forschungszentrum Karlsruhe 31/2001, http://hikwww9.fzk.de/aktuelles/presseinfo/2001/PI31_2001.html. 38- Südzucker Annual Report, 2002 http://www.suedzucker.de/downloads/04_investor_relations/gb_2002. pdf. 39- M. Gudmundsson, H. Hafsteinsson Trends Food Sci. Technol. 12, 2001, 3-4, 122-128. 40- B.L. Qin, U.R. Pothakamury, M. Vega, O. Martin, G.V. BarbosaCanovas, B.V. Swanson Food Technology, 49, 1995, 12, 55-60.

30-B.-L. Quin et al. Food Technol. 49, 1995, 55-60. 31- B.L. Qin, F.J. Chang, G.V. Barbosa-Canovas, B.G. Swanson, Lebensmittelwiss. u. Technol. 28, 1995, 564-568. 32- S. Ho, G.S. Mittal Food Rev. Internat. 16, 2000, 4, 395-434.

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4- New high (radio) frequency and microwave methods High frequency and microwaves are electromagnetic waves each in defined frequency ranges. Figure 1 shows how the frequency ranges are assigned [1]. Radio & TV

Mobile phone

Microwaves

Further background information on the usual high frequency and microwave applications in the food sector are to be found, for example, in [2] and [3] and the references cited there. Water and salt containing foods can often be heated very rapidly and penetratingly by means of high frequency or microwaves. This means that heat does not have to be conveyed from the outside into the inside of the product by slow thermal conduction, which is the basis for the quality advantages of microwave-processed foods. On the other hand, problems are reported in the uniformity of the temperature distribution in foods heated by high frequency and microwaves.

Frequency-Hz Wavelength-m

Low-frequency fields

High frequency fields

Optical radiation

Fig. 1: Spectrum of electromagnetic radiation [1]. At even higher frequencies or shorter wavelengths, ultraviolet, X and gamma rays follow. The high frequency applications operate in the range labelled radio and TV.

For applications on the other side of telecommunications and radar, socalled ISM (industrial, scientific, medical) bands exist which, as the name already suggests, are reserved for industrial, scientific and medical purposes and in which other applications have to tolerate certain (interference) radiation outputs. An overview of the ISM bands mainly used for food treatment is summarised in Table 1. Range

ISM frequencies

High frequency

13.56 MHz ± 0.05 % 27.12 MHz ± 0.60 % 40.68 MHz ± 0.05 %

Microwaves

ª 900 MHz (depending on the country) 2450 MHz ± 50 MHz

In the following, EU-financed projects are described in which a standard method for microwave ovens for determining the uniformity of their heating [4] and control strategies for combined microwave/hot air ovens [5] are being developed. Further on, projects which show the advantages of foods processed by high frequency or microwaves [6,7] are reported. 4.1 Standard method for determining the uniformity of heating in microwave ovens The aim of this method is objective testing of the uniformity of heating in various microwave ovens. When drawing up the method, particular care was taken that, while respecting the reproducibility and applicability to all commercially available domestic microwave appliances, it is based as closely as possible on the reality of use of microwave ovens in the home. In addition to the quality of the foods, the microbiological safety was defined as a test parameter. Two model foods were developed for this, which avoid the natural variability intrinsic in biological material but at the same time are similar

Tab. 1: Overview of the usual ISM frequency bands for food treatment 42

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to true refrigerated foods in their thermal and dielectric properties. Two different packagings based on actual food packagings can also be used. To determine the temperature distributions, 12 fibre-optic temperature sensors and infra-red cameras are used «inline» during the heating, while after the heating the temperature distribution is recorded with 39 thermocouples. The method is conducted with the aid of a precisely defined measurement protocol, in which the test conditions (nature, shape, production and storage of the model food, central positioning in the microwave oven, power setting) are specified to ensure optimum reproducibility. The data are evaluated by means of a computer which assess the «quality» of the microwave oven investigated in respect of food quality and safety, determined with the aid of the temperature uniformity and water loss. In addition to the data measured, this quality is specified with a characteristic index which allows simple comparison between different microwave ovens. To increase the acceptance of this characteristic index, its determination algorithm is being developed in collaboration with end-users, consumer centres, microwave and food producers, representatives of the IEC (International Electrotechnical Commission), CENELEC (European Committee for Electrotechnical Standardization) and microwave experts 4.2 Optimum control of microwave combination ovens for heating foods Microwave combination ovens in which the microwave heating is combined with hot air heating are becoming more and more popular in Europe. They are said to overcome the problems which exist in conventional microwave ovens, such as a non-uniform temperature distribution, while at the same time retaining the high heating speed.

The problem of these combination ovens is that the use of the two heating modes makes the instructions for use and the use itself more complicated. In the project described here, the use of such combination ovens was optimised with a view to maximising temperature uniformity and quality of the food. First, models and software for calculating the heating of food in combination ovens were developed, followed by methods of evaluating the temperature variation with a variable starting product quality. The heating process was quantified here, in the same way as in [4], by «quality factors» which take into account microbiological safety. Robust online controls which seek to achieve optimum heating even under varying product and process conditions were then drawn up with these parameters. It was found that the best results were achieved by means of a short microwave pulse at the start of heating, followed by subsequent hot air heating. 4.3 Electromagnetic heating processes for food production The aim of this project was to develop microwave and high frequency processes to make possible better food product qualities in respect of microbiology, enzyme activity and chemical composition. While microwave treatments concentrated on enzyme inactivation in wheat, parboiling of rice, drying of yellow beans and microbiological inactivation of herbs, soya beans and mustard grains were treated by means of high frequency for enzyme inactivation. The following promising results were achieved: - The drying time of «parboiled» rice could be reduced by up to 94% compared with the conventional process.

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- The nutritional value of yellow beans could be improved by combination of germination with conventional and microwave drying. - The germ count in herbs could be reduced by up to 103 with only small losses in flavours by microwave heating. - The baking quality of wheat flour can be increased by inactivating the heat-resistant alpha-amylase while preserving the heat-sensitive gluten-forming protein. This process depends greatly on the initial water content and can sometimes be achieved with a very short but intense microwave pulse with simultaneous cooling with air. - High frequency treatments on soya beans can reduce the trypsin inhibitor activity by 16-23%, depending on the final temperature reached and the pre-moistening level. - In the case of mustard grains, the composition (amino acids and fatty acids) and the sensory quality are not changed by high frequency treatments, while the cholesterol content is lowered. After the treatment the number of colony-forming units was less than 104 CFU/g. As a «by-product» of the project a high frequency pilot plant has been developed to treat mustard grains for inactivation of myrosinase and therefore to produce mild mustard. At an output of 40 kW (at 27.12 MHz), it achieves a throughput of 250 kg/h at half the investment costs of a conventional plant. Since October 2000, it has been operating industrially in Hungary and is therefore the only industrial high frequency cereal treatment plant in Europe. 4.4 Radio frequency heating technology for minimally-processed fish products In this current project the potential of high frequency heating for the production of minimally-processed cook/chill or cook/freeze fish products is being determined. Starting from existing vacuum-packed products which have been conventionally heat-treated, high frequency heating at 27.12 MHz is used to bring the fish products quickly (approximately 1-2 min instead of 30 min) to the desired temperature of 75 or 95ºC. The packaging is immersed in de-ionised water during the high frequency heating in order to make the heat treatment spatially uniform at a negligible high frequency energy loss.

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In addition to the uniformity and rapidity, the reproducibility, quality (texture, taste, colour, shelf life) and microbiological safety are the most important aims of the project. Experiments and models are also intended to validate the process and allow scale-up. Finally, the economic aspects of the method, the market and the distribution chain for appropriate products will also be observed. During the first year of this 3-year project, the high frequency plant (with the capability of temperature distribution measurement) was constructed and experiments and methods developed. An individual portion of cod and fillet of salmon, each vacuum-packed in flexible, high frequency-transparent, heat-resistant and relatively oxygen-tight film, were chosen as the fish products. The starting material was characterised in respect of composition, physical properties and microbiological state and methods for investigating the quality and microbiology of the raw and processed fish were chosen and tested. Two temperature regimes were defined on the basis of a microbiological risk analysis: A final temperature of more than 75ºC is said to inactivate all vegetative microorganisms and leads to a shelf life of 10 days at 4ºC, while a final temperature of 95ºC is said to inactivate even spores of pathogenic microorganisms which can grow under cool conditions, so that a shelf life of more than 20 days at 4ºC can be expected. First experiments resulted in heating rates of 1ºC/s in the high frequency plant constructed, with negligible heating of the de-ionised water, which can be produced inexpensively by an ion exchanger. Results on important quality features, such as water retention capacity, firmness and colour, were influenced positively by the rapid heating process in salmon samples. In the future years of the project, the desired outcomes should be achieved and may probably also be applied to other cooked/refrigerated foodstuffs.

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4.5 Further literature 1- Bundesamt für Strahlenschutz Strahlenschutz bei Radio- und Mikrowellen, http://www.bfs.de/bfs/druck/strahlenthemen/radio_mikrowellen.html, 2003. 2- A.T. Rowley Radio frequency heating, in: P. Richardson, Thermal technologies in food processing Woodhead Publishing Ltd, p. 163 – 177, 2001. 3- M. Regier, H. Schubert Microwave Processing, in: P. Richardson, Thermal technologies in food processing Woodhead Publishing Ltd, p. 178 – 207, 2001.

6- Electromagnetic heating processes for food production IC 1597 1001 (INCO) Project Coordinator: Mr S. James Food Refrigeration and Process Engineering Research Centre (frperc), University of Bristol, Churchill Building, Langford, Bristol, BS40 5DU, UK Tel : +44 (0)117 928 9239, Fax : +44 (0)117 928 9314 E-mail: [email protected] 7- RF-Fish Radio-frequency heating technology for minimally processed fish products QLK-CT-2001-01788 Project Coordinator: Dr. T. Pfeiffer Fraunhofer-Institut für Verfahrenstechnik und Verpackung, Giggenhauser Str. 35, D-85354 Freising, GERMANY Tel : +49 (0) 8161 491424, Fax : +49 (0) 8161 491444 E-mail: [email protected]

4- Determination of unsatisfactory temperature distributions within chilled foods heated in microwave ovens EU-Standards, Measurements and Testing Programme Food Refrigeration and Process Engineering Research Centre (frperc) University of Bristol, Churchill Building, Langford, Bristol, BS40 5DU, UK Tel : +44 (0)117 928 9239, Fax : +44 (0)117 928 9314; E-mail: [email protected] 5- Optimal control of microwave combination ovens for food heating FAIR-CT96-1192 Project Coordinator: Prof. B. Nicolai Katholieke Universiteit Leuven, de Cruylaan 42, BE-3001 Heverlee, BELGIUM Tel : +32 1632 2375, Fax : +32 1632 2955 E-mail: [email protected]

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