21 High pressure processing Indrawati, A. Van Loey and M. Hendrickx Katholieke Universiteit, Leuven 21.1 Introduction Food quality, including colour, texture, flavour and nutritional value, is of key importance in the context of food preservation and processing. Colour, texture and flavour refer to consumption quality, purchase and product acceptability whereas the nutritive values (i.e. vitamin content, nutrients, minerals, health related food components)refer to hidden quality aspects. In conventional thermal processing, process optimisation consists of reducing the severity of the thermal process in terms of food quality destruction without compromising food safety. Due to the consumer demand for fresher, healthier and more natural food prod ucts, high pressure technology is considered as a new and alternative unit opera tion in food processing and preservation 21.2 High pressure processing in relation to food quality and safety The effect of high pressure on food microorganisms was reported for the first time by Hite in 1899, by subjecting milk to a pressure of 650MPa and obtaining a reduction in the viable number of microbes. Some years later, the effect of high pressure on the physical properties of food was reported, e.g. egg albumin co- angulation(Bridgman, 1914), solid-liquid phase diagram of water(Bridgman, 1912)and thermophysical properties of liquids under pressure(Bridgman, 1923). A more extensive exploration of high pressure as a new tool in food technology started in the late 1980s(Hayashi, 1989). Recently, extensive research has been conducted and is in progress on
21 High pressure processing Indrawati, A. Van Loey and M. Hendrickx, Katholieke Universiteit, Leuven 21.1 Introduction Food quality, including colour, texture, flavour and nutritional value, is of key importance in the context of food preservation and processing. Colour, texture and flavour refer to consumption quality, purchase and product acceptability whereas the nutritive values (i.e. vitamin content, nutrients, minerals, healthrelated food components) refer to hidden quality aspects. In conventional thermal processing, process optimisation consists of reducing the severity of the thermal process in terms of food quality destruction without compromising food safety. Due to the consumer demand for fresher, healthier and more natural food products, high pressure technology is considered as a new and alternative unit operation in food processing and preservation. 21.2 High pressure processing in relation to food quality and safety The effect of high pressure on food microorganisms was reported for the first time by Hite in 1899, by subjecting milk to a pressure of 650 MPa and obtaining a reduction in the viable number of microbes. Some years later, the effect of high pressure on the physical properties of food was reported, e.g. egg albumin coagulation (Bridgman, 1914), solid–liquid phase diagram of water (Bridgman, 1912) and thermophysical properties of liquids under pressure (Bridgman, 1923). A more extensive exploration of high pressure as a new tool in food technology started in the late 1980s (Hayashi, 1989). Recently, extensive research has been conducted and is in progress on
434 The nutrition handbook for food processors possible applications of high pressure for food preservation purposes or for changing the physical and functional properties of foods. The potentials and limit ations of high pressure processing in food applications have become more clear. A number of key effects of high pressure on food components have been de- monstrated including (1) microorganism inactivation; (ii) modification of bio- polymers including enzyme activation and inactivation, protein denaturation and gel formation;(ii) quality retention (e.g. colour, flavour, nutrition value)and (iv) modification of physicochemical properties of water( Cheftel, 1991; Knorr, 1993). One of the unique characteristics of high pressure is that it directly affects non-covalent bonds(such as hydrogen, ionic, van der Waals and hydrophobic bonds)and very often leaves covalent bonds intact(Hayashi, 1989). As a conse- quence, it offers the possibility of retaining food quality attributes such as vita- mins(Van den Broeck et al, 1998), pigments( Van Loey et al, 1998)and flavour components, while activating microorganisms and food-quality related enzymes, changing the structure of food system and functionality of food pro- teins(Hoover et al, 1989; Knorr 1995: Barbosa- Canovas et al, 1997; Messens et al, 1997; Hendrickx et al, 1998). Furthermore, by taking advantage of the effect on the solid liquid phase transition of water, some potential applications in food processing such as pressure-assisted freezing(pressure shift freezing), pres ssure assisted thawing(pressure shift thawing), non-frozen storage under pressure at subzero temperature and formation of different ice polymorphs can be offered while keeping other food quality properties(Kalichevsky et al, 1995). Beside pressure can also induce increased biochemical reaction rates with effect on bio- conversions and metabolite production(Tauscher, 1995). Based on these effects of high pressure on food systems, several potential applications can be identified such as high pressure pasteurisation of fruit and vegetables products(Parish, 1994: Yen and Lin, 1996), tenderisation of meat products(Elgasim and Kennick, 1980; Ohmori et al, 1991; Cheftel and Culioli, 1997), texturisation of fish pro- teins, applications in the dairy industry(Messens et al, 1997) and high pressure freezing/thawing(Kalichevsky et al, 1995) With regard to food safety, the effect of combined high pressure and tem- perature on microorganisms has been investigated extensively (Sonoike et al 1992: Hashizume et al, 1995; Knorr, 1995: Heinz and knorr 1996: Hauben, 1998; Reyns et al, 2000). The number of vegetative cells can be remarkably reduced by applying pressures up to 400 MPa combined with moderate temperatures up to 40C for 10-30 minutes(Knorr, 1995). On the other hand, exposing the sur- viving fraction of vegetative cells to repeated pressure cycles can also increase their pressure resistance, e.g. Escherichia coli mutants resistant to high pressure inactivation were created (Hauben, 1998; Alpas et al, 1999: Benito et al, 1999) Microbial spores can be inactivated by exposure to high pressure but a pressure treatment at room temperature may not be sufficient for substantial reduction of viable spore counts. Most studies show that pressure can induce spore germina- tion and the extent of spore inactivation can be increased by increasing pressure and temperature(Knorr, 1995; Wuytack, 1999). However, tailing phenomena for germination and inactivation curves can occur for 'super dormant spores after
possible applications of high pressure for food preservation purposes or for changing the physical and functional properties of foods. The potentials and limitations of high pressure processing in food applications have become more clear. A number of key effects of high pressure on food components have been demonstrated including (i) microorganism inactivation; (ii) modification of biopolymers including enzyme activation and inactivation, protein denaturation and gel formation; (iii) quality retention (e.g. colour, flavour, nutrition value) and (iv) modification of physicochemical properties of water (Cheftel, 1991; Knorr, 1993). One of the unique characteristics of high pressure is that it directly affects non-covalent bonds (such as hydrogen, ionic, van der Waals and hydrophobic bonds) and very often leaves covalent bonds intact (Hayashi, 1989). As a consequence, it offers the possibility of retaining food quality attributes such as vitamins (Van den Broeck et al, 1998), pigments (Van Loey et al, 1998) and flavour components, while inactivating microorganisms and food-quality related enzymes, changing the structure of food system and functionality of food proteins (Hoover et al, 1989; Knorr, 1995; Barbosa-Cànovas et al, 1997; Messens et al, 1997; Hendrickx et al, 1998). Furthermore, by taking advantage of the effect on the solid liquid phase transition of water, some potential applications in food processing such as pressure-assisted freezing (pressure shift freezing), pressureassisted thawing (pressure shift thawing), non-frozen storage under pressure at subzero temperature and formation of different ice polymorphs can be offered while keeping other food quality properties (Kalichevsky et al, 1995). Besides, pressure can also induce increased biochemical reaction rates with effect on bioconversions and metabolite production (Tauscher, 1995). Based on these effects of high pressure on food systems, several potential applications can be identified such as high pressure pasteurisation of fruit and vegetables products (Parish, 1994; Yen and Lin, 1996), tenderisation of meat products (Elgasim and Kennick, 1980; Ohmori et al, 1991; Cheftel and Culioli, 1997), texturisation of fish proteins, applications in the dairy industry (Messens et al, 1997) and high pressure freezing/thawing (Kalichevsky et al, 1995). With regard to food safety, the effect of combined high pressure and temperature on microorganisms has been investigated extensively (Sonoike et al, 1992; Hashizume et al, 1995; Knorr, 1995; Heinz and Knorr, 1996; Hauben, 1998; Reyns et al, 2000). The number of vegetative cells can be remarkably reduced by applying pressures up to 400 MPa combined with moderate temperatures up to 40°C for 10–30 minutes (Knorr, 1995). On the other hand, exposing the surviving fraction of vegetative cells to repeated pressure cycles can also increase their pressure resistance, e.g. Escherichia coli mutants resistant to high pressure inactivation were created (Hauben, 1998; Alpas et al, 1999; Benito et al, 1999). Microbial spores can be inactivated by exposure to high pressure but a pressure treatment at room temperature may not be sufficient for substantial reduction of viable spore counts. Most studies show that pressure can induce spore germination and the extent of spore inactivation can be increased by increasing pressure and temperature (Knorr, 1995; Wuytack, 1999). However, tailing phenomena for germination and inactivation curves can occur for ‘super dormant’ spores after 434 The nutrition handbook for food processors
High pressure processing 435 long exposure times. As a consequence, to achieve sterility with minimal impact on nutrition value, flavour, texture and colour, high pressure processing using multiple high pressure pulses and achieving an end temperature above 105oC under pressure for a short time has been proposed(Meyer et al, 2000; Krebbers etal,2001) 21.3 High pressure technology and equipment for the food industry High pressure technology has been used in the industrial production process of ceramics, metals and composites in the last three decennia. As a result, today, high pressure equipment is available for a broad range of process con- ditions, i.e. pressures up to 1000MPa, temperatures up to 2200C, volumes up to several cubic meters and cycling times between a few seconds and several Since high pressure technology offers advantages in retaining food quality attributes, it has recently been the subject of considerable interest in the food industry as a non-thermal unit operation. High pressure equipment with pressure levels up to 800 MPa and temperatures in the range of 5 to 90C(on average)for times up to 30 minutes or longer is currently available to the food industry The actual high pressure treatment is a batch process. In practice, high pres- Ire technology subjects liquid or solid foods, with or without packaging, to pres- sures between 50 and 1000 MPa. According to Pascals principle, high pressure acts instantaneously and uniformly throughout a mass of food and is independent of the size and shape of food products. During compression, a temperature increase or adiabatic heating occurs and its extent is influenced by the rate of pressurisation, the food composition and the( thermo)physical properties of the pressure transfer medium. The temperature in the vessel tends to equilibrate towards the surrounding temperature during the holding period. During pressure release(decompression), a temperature decrease or adiabatic cooling takes place In high pressure processing, heat cannot be transferred as instantaneously and uniformly as pressure so that temperature distribution in the vessel might become crucial. During the high pressure treatment, other process parameters such as treatment time, pressurisation/decompression rate and the number of pulses have to be considered as critical L. Two types of high pressure equipment can be used in food processing: con- entional batch systems and semi-continuous systems. In the conventional batch systems, both liquid and solid pre-packed foods can be processed whereas only pumpable food products such as fruit juice can be treated in semi-continuous systems. Typical equipment for batch high pressure processing consists of a cylin drical steel vessel of high tensile strength, two end closures, a means for restrain ing the end closures(e g a closing yoke to cope with high axial forces, thread pins),(direct or indirect) compression pumps and necessary pressure controls and
long exposure times. As a consequence, to achieve sterility with minimal impact on nutrition value, flavour, texture and colour, high pressure processing using multiple high pressure pulses and achieving an end temperature above 105°C under pressure for a short time has been proposed (Meyer et al, 2000; Krebbers et al, 2001). 21.3 High pressure technology and equipment for the food industry High pressure technology has been used in the industrial production process of ceramics, metals and composites in the last three decennia. As a result, today, high pressure equipment is available for a broad range of process conditions, i.e. pressures up to 1000 MPa, temperatures up to 2200°C, volumes up to several cubic meters and cycling times between a few seconds and several weeks. Since high pressure technology offers advantages in retaining food quality attributes, it has recently been the subject of considerable interest in the food industry as a non-thermal unit operation. High pressure equipment with pressure levels up to 800 MPa and temperatures in the range of 5 to 90°C (on average) for times up to 30 minutes or longer is currently available to the food industry. The actual high pressure treatment is a batch process. In practice, high pressure technology subjects liquid or solid foods, with or without packaging, to pressures between 50 and 1000 MPa. According to Pascal’s principle, high pressure acts instantaneously and uniformly throughout a mass of food and is independent of the size and shape of food products. During compression, a temperature increase or adiabatic heating occurs and its extent is influenced by the rate of pressurisation, the food composition and the (thermo)physical properties of the pressure transfer medium. The temperature in the vessel tends to equilibrate towards the surrounding temperature during the holding period. During pressure release (decompression), a temperature decrease or adiabatic cooling takes place. In high pressure processing, heat cannot be transferred as instantaneously and uniformly as pressure so that temperature distribution in the vessel might become crucial. During the high pressure treatment, other process parameters such as treatment time, pressurisation/decompression rate and the number of pulses have to be considered as critical. Two types of high pressure equipment can be used in food processing: conventional batch systems and semi-continuous systems. In the conventional batch systems, both liquid and solid pre-packed foods can be processed whereas only pumpable food products such as fruit juice can be treated in semi-continuous systems. Typical equipment for batch high pressure processing consists of a cylindrical steel vessel of high tensile strength, two end closures, a means for restraining the end closures (e.g. a closing yoke to cope with high axial forces, threads, pins), (direct or indirect) compression pumps and necessary pressure controls and High pressure processing 435
436 The nutrition handbook for food processo instrumentation. Different types of high pressure vessels can be distinguished, 1.e (i)'monobloc vessel(a forged constructed in one piece);(ii)multi layer vessel consisting of multiple layers where the inner layers are pre-stressed to reach pressure or(iii)wire wound vessel cons sisting of pre-stressed vessels formed by winding a rectangular spring steel wire around the vessel. The use of monobloc vessels is limited to working pressures up to 600 MPa and for high pressure application above 600MPa, pre-stressed vessels are used. The position of high pressure vessels can be vertical, horizontal or tilting depending on the way of processing(Mertens and Deplace, 1993; Zimmerman and Bergman, 1993 Galazka and Ledward, 1995; Mertens, 1995: Knorr, 2001) 21.4 Commercial high pressure treated food products With regard to the large-scale application of high pressure technology in the food industry, a problem still to be solved today is the improvement of the economic feasibility, i.e. the high investment cost mainly associated with the high capital cost for a commercial high pressure system. The cost of a vessel is determined y the required working pressure/temperature and volume. Furthermore, once technically and economically feasible processes have been identified, one needs to evaluate whether the unique properties of the food justify the additional cost and to what extent consumers are willing to pay a higher price for a premium ity produc High pressure technology is unlikely to replace conventional thermal pro- tood g, because the second \echnique is a well-established and relatively cheap food preservation method. Currently, the reported cost range of high pressure processes is 0. 1-0.2S per litre(Grant et al, 2000) whereas the cost for thermal treatment may be as low as 0.02-0.04$ per litre. However, the technology offers commercially feasible alternatives for conventional heating in the case of novel food products with improved functional properties which cannot be attained by conventional heating Today, several commercial high pressure food products are available in Japan, Europe and the United States. A Japanese company, Meidi-Ya, introduced the first commercial pressure treated product(a fruit-based jam) on the market in April 1990, followed in 1991 by a wide variety of pressure-processed fruit yoghurts, fruit jellies, fruit sauces, savoury rice products, dessert and salad dress ings(Mertens and Deplace, 1993). Recently, there were more than 10 pressure treated food products available in Japan. In Europe, fruit juice was the first commercially available high pressure product in France followed by a pressurised delicatessen style ham in Spain and pressurised orange juice in the United Kingdom. In the United States, high pressure treated guacamole has been launched on the commercial market. In addition, pressure treated oysters and hummus are commercially available. A list of commercially available pressurised food products in Japan, Europe and the United States in the last decade is sum- marised in Table 21.1
instrumentation. Different types of high pressure vessels can be distinguished, i.e. (i) ‘monobloc vessel’ (a forged constructed in one piece); (ii) ‘multi layer vessel’ consisting of multiple layers where the inner layers are pre-stressed to reach higher pressure or (iii) ‘wire-wound vessel’ consisting of pre-stressed vessels formed by winding a rectangular spring steel wire around the vessel. The use of monobloc vessels is limited to working pressures up to 600 MPa and for high pressure application above 600 MPa, pre-stressed vessels are used. The position of high pressure vessels can be vertical, horizontal or tilting depending on the way of processing (Mertens and Deplace, 1993; Zimmerman and Bergman, 1993; Galazka and Ledward, 1995; Mertens, 1995; Knorr, 2001). 21.4 Commercial high pressure treated food products With regard to the large-scale application of high pressure technology in the food industry, a problem still to be solved today is the improvement of the economic feasibility, i.e. the high investment cost mainly associated with the high capital cost for a commercial high pressure system. The cost of a vessel is determined by the required working pressure/temperature and volume. Furthermore, once technically and economically feasible processes have been identified, one needs to evaluate whether the unique properties of the food justify the additional cost and to what extent consumers are willing to pay a higher price for a premium quality product. High pressure technology is unlikely to replace conventional thermal processing, because the second technique is a well-established and relatively cheap food preservation method. Currently, the reported cost range of high pressure processes is 0.1–0.2 $ per litre (Grant et al, 2000) whereas the cost for thermal treatment may be as low as 0.02–0.04 $ per litre. However, the technology offers commercially feasible alternatives for conventional heating in the case of novel food products with improved functional properties which cannot be attained by conventional heating. Today, several commercial high pressure food products are available in Japan, Europe and the United States. A Japanese company, Meidi-Ya, introduced the first commercial pressure treated product (a fruit-based jam) on the market in April 1990, followed in 1991 by a wide variety of pressure-processed fruit yoghurts, fruit jellies, fruit sauces, savoury rice products, dessert and salad dressings (Mertens and Deplace, 1993). Recently, there were more than 10 pressure treated food products available in Japan. In Europe, fruit juice was the first commercially available high pressure product in France followed by a pressurised delicatessen style ham in Spain and pressurised orange juice in the United Kingdom. In the United States, high pressure treated guacamole has been launched on the commercial market. In addition, pressure treated oysters and hummus are commercially available. A list of commercially available pressurised food products in Japan, Europe and the United States in the last decade is summarised in Table 21.1. 436 The nutrition handbook for food processors
High pressure processing 437 21.5 Effect of high pressure on vitamins Many authors have reported that the vitamin content of fruit and vegetable prod ucts is not significantly affected by high pressure processing. According to Bignon(1996), a high pressure treatment can maintain vitamins C, A, B,, B2, E and folic acid and the decrease of vitamin C in pressurised orange juice is ligible as compared to flash pasteurised juices during storage at 4C for 40 da Similar findings have been reported for red orange juice; high pressure (200- 500MPa/30C/1 min) did not affect the content of several vitamins(vitamins C, B1, B2, Bs and niacin)(Donsi et al, 1996) 21.5.1 Ascorbic acid he effect of high pressure treatment on ascorbic acid has been more intensively studied than on vitamins such asa.b.d.e and k studies on ascorbic acid stability in various food products after high pressure treatment are available Most authors have reported that the ascorbic acid content is not significantly affected by high pressure treatment. For example, in fruit and vegetables, about 82%o of the ascorbic acid content in fresh green peas can be retained after pres sure treatment at 900 MPa/20C for 5-10 minutes(Quaglia et al, 1996). Almost 95-99%o of the vitamin C content in strawberry and kiwi jam can be preserved by pressurisation between 400 and 600MPa for 10-30min(Kimura, 1992; Kimura et al, 1994). In freshly squeezed citrus juices, high pressures up to 600MPa at 23C for 10 min did not affect the initial(total and dehydro)ascor bic acid concentration(Ogawa et al, 1992). Similar findings are also reported in strawberry ' coulis'(a common sauce in French dessert) and strawberry nectar the vitamin C content was preserved after 400MPa/20C/30min(88.68% of the initial content in fresh sample) and in guava puree, high pressure(400 and 600MPa/15 min) maintained the initial concentration of ascorbic acid (Yen and Lin, 1996). Also, ascorbic acid stability in egg yolk has been investigated showing that high pressure treatment(200, 400, 600MPa) at 20oC for 30 min did not significantly affect the vitamin C content(Sancho et al, 1999). The evolution of the vitamin C content in high pressure treated food products during storage has also been investigated. Most studies show that storage at low temperature can eliminate the vitamin C degradation after high pressure treat- 2-3 months at 5C but a deterioration of vitamin C was noly unchanged for ment. For example, the quality of high pressure treated jam was unchanged for at 25C(Kimura, 1992; Kimura et al, 1994). Another study on strawberry nectar showed that ascorbic acid remained practically the same during high pressure processing(500MPa/room temperature/3 min) but decreased during storage(up to 75%o of the initial concentration after storage for 60 days at 3C)(Rovere et al, 1996). In valencia orange juice, the percentage of ascorbic acid in pressurised juice(500-700MPa/50-60.C/60-90s) was 20-45% higher than in heat treated juice(98 C/10s) during storage at 4 and 8C for 20 weeks(Parish, 1997) Studies on guava puree showed that different high pressure processes have a
21.5 Effect of high pressure on vitamins Many authors have reported that the vitamin content of fruit and vegetable products is not significantly affected by high pressure processing. According to Bignon (1996), a high pressure treatment can maintain vitamins C, A, B1, B2, E and folic acid and the decrease of vitamin C in pressurised orange juice is negligible as compared to flash pasteurised juices during storage at 4°C for 40 days. Similar findings have been reported for red orange juice; high pressure (200– 500 MPa/30°C/1 min) did not affect the content of several vitamins (vitamins C, B1, B2, B6 and niacin) (Donsì et al, 1996). 21.5.1 Ascorbic acid The effect of high pressure treatment on ascorbic acid has been more intensively studied than on vitamins such as A, B, D, E and K. Studies on ascorbic acid stability in various food products after high pressure treatment are available. Most authors have reported that the ascorbic acid content is not significantly affected by high pressure treatment. For example, in fruit and vegetables, about 82% of the ascorbic acid content in fresh green peas can be retained after pressure treatment at 900 MPa/20°C for 5–10 minutes (Quaglia et al, 1996). Almost 95–99% of the vitamin C content in strawberry and kiwi jam can be preserved by pressurisation between 400 and 600 MPa for 10–30 min (Kimura, 1992; Kimura et al, 1994). In freshly squeezed citrus juices, high pressures up to 600 MPa at 23°C for 10 min did not affect the initial (total and dehydro) ascorbic acid concentration (Ogawa et al, 1992). Similar findings are also reported in strawberry ‘coulis’ (a common sauce in French dessert) and strawberry nectar; the vitamin C content was preserved after 400 MPa/20°C/30 min (88.68% of the initial content in fresh sample) and in guava purée, high pressure (400 and 600 MPa/15 min) maintained the initial concentration of ascorbic acid (Yen and Lin, 1996). Also, ascorbic acid stability in egg yolk has been investigated, showing that high pressure treatment (200, 400, 600 MPa) at 20°C for 30 min did not significantly affect the vitamin C content (Sancho et al, 1999). The evolution of the vitamin C content in high pressure treated food products during storage has also been investigated. Most studies show that storage at low temperature can eliminate the vitamin C degradation after high pressure treatment. For example, the quality of high pressure treated jam was unchanged for 2–3 months at 5°C but a deterioration of vitamin C was noticed during storage at 25°C (Kimura, 1992; Kimura et al, 1994). Another study on strawberry nectar showed that ascorbic acid remained practically the same during high pressure processing (500 MPa/room temperature/3 min) but decreased during storage (up to 75% of the initial concentration after storage for 60 days at 3°C) (Rovere et al, 1996). In valencia orange juice, the percentage of ascorbic acid in pressurised juice (500–700 MPa/50–60°C/60–90 s) was 20–45% higher than in heat treated juice (98°C/10 s) during storage at 4 and 8°C for 20 weeks (Parish, 1997). Studies on guava purée showed that different high pressure processes have a High pressure processing 437
Table 21.1 Commercial pressurised food products in Japan, Europe and the United States in the last ten years(after Cheftel, 1997) Company Product P/T/time combination Role of hp JAPAN Meidi-ya Fruit based products(pH 4.5); jams 400MPa, 10-30min, Pasteurisation, improved gelation, faster sugar 3 (apple, kiwi, strawberry): jellies 20°C penetration; limiting residual purees; yoghurts: sauces pectinmethylesterase activity Pokka Corp(stopped Grapefruit juice 200 MPa 10-15min. Reduced bittern 5°C Wakayama Food Ind Mandarin juice(winter season only) 300-400 MPa, 2-3 Reduced odor of dimethyl sulphide; reduced (only≈20% of HP juice in final juice20°C thermal degradation of methyl methionine sulphoxide: replace hrst thermal pasteurisation 2 before packing: 90C, 3 Nisshin fine foods Sugar impregnated tropical fruits(kept 50-200MPa Faster sugar penetration and water removal at-18C without freezing). For sorbet and ice cream Fuji chiku mutterham Raw pork ham 250MPa. 3 hours Faster maturation (reduced from 2 weeks to 3 hours); faster tenderisation by internal proteases, improved water retention and shelf Kibun(stopped in Shiokara and raw scallops Microbial sanitation. tenderisation. control autolysis by endogenous proteases Yaizu fisheries(test Fish sausages, terrines and 'pudding 400 MPa Gelation, microbial sanitation, good texture of raw hP gel Raw’sake( rice wine Yeast inactivation, fermentation stopped without heating
438 The nutrition handbook for food processors Table 21.1 Commercial pressurised food products in Japan, Europe and the United States in the last ten years (after Cheftel, 1997) Company Product P/T/time combination Role of HP JAPAN Meidi-ya Fruit based products (pH < 4.5); jams 400 MPa, 10–30 min, Pasteurisation, improved gelation, faster sugar (apple, kiwi, strawberry); jellies; 20 °C penetration; limiting residual purées; yoghurts; sauces pectinmethylesterase activity Pokka Corp. (stopped Grapefruit juice 200 MPa, 10–15 min, Reduced bitterness c2000–2001) 5 °C Wakayama Food Ind. Mandarin juice (winter season only) 300–400 MPa, 2–3 min, Reduced odor of dimethyl sulphide; reduced (only 20% of HP juice in final juice 20 °C thermal degradation of methyl methionine mix) sulphoxide; replace first thermal pasteurisation (after juice extraction) and final pasteurisation before packing: 90 °C, 3 min Nisshin fine foods Sugar impregnated tropical fruits (kept 50–200 MPa Faster sugar penetration and water removal at -18 °C without freezing). For sorbet and ice cream Fuji chiku mutterham Raw pork ham 250 MPa, 3 hours, Faster maturation (reduced from 2 weeks to 20 °C 3 hours); faster tenderisation by internal proteases, improved water retention and shelf life Kibun (stopped in ‘Shiokara’ and raw scallops / Microbial sanitation, tenderisation, control of 1995) autolysis by endogenous proteases Yaizu fisheries (test Fish sausages, terrines and ‘pudding’ 400 MPa Gelation, microbial sanitation, good texture of market only) raw HP gel Chiyonosono ‘Raw’ sake (rice wine) / Yeast inactivation, fermentation stopped without heating
Table 21.1 Commercial pressurised food products in Japan, Europe and the United States in the last ten years(after Cheftel, 1997) Company Product P/T/time combination Role of HP Ice nucleating bacteria(for fruit juice Inactivation of Xanthomonas. no loss of ice and milk) Japanese mandarin juice Echigo seika Moci rice cake, Yomogi fresh aromatic 400-600 MPa, 10min, Microbial reduction, fresh flavour and taste, erbs, hypoallergenic precooked rice 45or70° enhances rice porosity and salt extraction of convenience packs of boiled rice Takansi Fruit juice Pon(test mar Orange juice EUROPE pry(france) Fruit juice(orange, grape fruit, citrus, 400MPa, room Inactivation of micro flora(up to 10CFU/g) mixed fruit juice) temperature partial inactivation of pectinmethylesterase Espuna(Spain) Deli-style processed meats(ham) 400-500 MPa, few ninutes room temperature Orchard house Squeezed orange juice 500MPa. room Inactivation of micro flora(especially yea Ltd. ( UK)(since temperature and enzyme, keeping natt 2001) THE UNITED STATES Avocado paste(guacamole, chipotle 700 MPa, 10-15 min, Micro m inactivation, polyphenoloxidase sauce, salsa) and pieces 20°C nactivation, chilled process Nisbet 300-400MPa, roor Microorganism inactivation, keeping raw taste loey Oyster temperature, 10 m and flavour, no change in shape and size E080≌= ternational Foods indicates no detailed information available
High pressure processing 439 QP corp Ice nucleating bacteria (for fruit juice / Inactivation of Xanthomonas, no loss of ice and milk) nucleating properties Ehime co. Japanese mandarin juice / Cold pasteurisation Echigo seika Moci rice cake, Yomogi fresh aromatic 400–600 MPa, 10 min, Microbial reduction, fresh flavour and taste, herbs, hypoallergenic precooked rice, 45 or 70°C enhances rice porosity and salt extraction of convenience packs of boiled rice allergenic proteins Takansi Fruit juice / Cold pasteurisation Pon (test market in Orange juice / / 2000) EUROPE Pampryl (France) Fruit juice (orange, grape fruit, citrus, 400 MPa, room Inactivation of micro flora (up to 106CFU/g), mixed fruit juice) temperature partial inactivation of pectinmethylesterase Espuna (Spain) Deli-style processed meats (ham) 400–500 MPa, few / minutes, room temperature Orchard House Foods Squeezed orange juice 500 MPa, room Inactivation of micro flora (especially yeast) Ltd. (UK) (since July temperature and enzyme, keeping natural taste 2001) THE UNITED STATES Avomex Avocado paste (guacamole, chipotle 700 MPa, 10–15 min, Microorganism inactivation, polyphenoloxidase sauce, salsa) and pieces 20°C inactivation, chilled process Motivatit, Nisbet Oysters 300–400 MPa, room Microorganism inactivation, keeping raw taste Oyster Co, Joey Oyster temperature, 10 minutes and flavour, no change in shape and size Hannah International Hummus / / Foods / indicates no detailed information available. Table 21.1 Commercial pressurised food products in Japan, Europe and the United States in the last ten years (after Cheftel, 1997) Company Product P/T/time combination Role of HP Continued
440 The nutrition handbook for food processors different influence on the stability of vitamin C during storage. The ascorbic acid content in untreated and pressurised (400 MPa/room temperature/15 min) guava puree started to decline respectively after 10 and 20 days whereas that in heated (88-90C/24s)and( 600 MPa/room temperature/15 min) pressurised guava puree remained constant during 30 and 40 days respectively (Yen and Lin, 1996) Kinetics of vitamin C degradation during storage have been studied in high pressure treated strawberry coulis. Vitamin C degradation of pressurised (400 MPa/20oC/30 min) and untreated coulis are nearly identical during storage at 4C. Moreover, it has been shown that a pressure treatment neither accelerates nor slows down the kinetic degradation of ascorbic acid during subsequent storage(Sancho et al, 1999) The effect of oxygen on ascorbic acid stability under pressure has been studied by Taoukis and co-workers(1998). At 600 MPa and 75C for 40 min exposed to air, ascorbic acid in buffer solution(sodium acetate buffer(0. 1 M: pH 3.5-4)) degraded to 45%o of its initial content while in the absence of oxygen, less vitamin loss was observed. Moreover, the addition of 10% sucrose resulted in a protec tive effect on ascorbic acid degradation. It was also noted that vitamin C loss was higher in fruit juice compared to that in buffer solutions. Vitamin C loss in pine- apple and grapefruit juice after pressurisation(up to 600 MPa and 75C)was max 70%o and 50% respectively. At constant pressure(600 MPa after 40 min), the pres- sure degradation of vitamin C in pineapple juice was temperature sensitive, e.g loss 20-25% at 40C. 45-50% at 60C and 60-70% at 75C in contrast to that in grapefruit juice. Detailed kinetics of combined pressure and temperature stability of ascorbic acid in different buffer(pH 4, 7 and 8)systems and real products(squeezed orange and tomato juices) have been carried out by Van den Broeck and co- workers(1998). At 850MPa and 50C for 1 hour, no ascorbic acid loss was observed. The high pressure/thermal degradation of ascorbic acid at 850 MPa and 65-80oC followed a first order reaction the rate of ascorbic acid degradation at 850 MPa increased with increasing temperature from 65 to 80C indicating that pressure and temperature act synergistically. Ascorbic acid in tomato juice was more stable than in orange juice. It was also reported that temperature depend- ence of ascorbic acid degradation(z value)was independent of the pressure level Based on this study, it can be concluded that ascorbic acid is unstable at high pressure(850MPa)in combination with high temperature(65-80oC) 21.5.2 Vitamin a and carotene The effect of high pressure treatment on carotene stability has been studied in carrots and in mixed juices. Based on the available literature data, we can con- clude that high pressure treatment does not affect (or affects only slightly) the carotene content in food products. a-and B-carotene contents in carrot puree were only slightly affected by pressure exposure at 600MPa and 75.C for 40 min (Tauscher, 1998). Similar findings have also been reported by de acos and co- workers(2000)showing that carotene loss in carrot homogenates and carrot paste
different influence on the stability of vitamin C during storage. The ascorbic acid content in untreated and pressurised (400 MPa/room temperature/15 min) guava puree started to decline respectively after 10 and 20 days whereas that in heated (88–90°C/24 s) and (600 MPa/room temperature/15 min) pressurised guava purée remained constant during 30 and 40 days respectively (Yen and Lin, 1996). Kinetics of vitamin C degradation during storage have been studied in high pressure treated strawberry coulis. Vitamin C degradation of pressurised (400 MPa/20°C/30 min) and untreated coulis are nearly identical during storage at 4°C. Moreover, it has been shown that a pressure treatment neither accelerates nor slows down the kinetic degradation of ascorbic acid during subsequent storage (Sancho et al, 1999). The effect of oxygen on ascorbic acid stability under pressure has been studied by Taoukis and co-workers (1998). At 600 MPa and 75°C for 40 min exposed to air, ascorbic acid in buffer solution (sodium acetate buffer (0.1 M; pH 3.5–4)) degraded to 45% of its initial content while in the absence of oxygen, less vitamin loss was observed. Moreover, the addition of 10% sucrose resulted in a protective effect on ascorbic acid degradation. It was also noted that vitamin C loss was higher in fruit juice compared to that in buffer solutions. Vitamin C loss in pineapple and grapefruit juice after pressurisation (up to 600 MPa and 75°C) was max. 70% and 50% respectively. At constant pressure (600 MPa after 40min), the pressure degradation of vitamin C in pineapple juice was temperature sensitive, e.g. loss 20–25% at 40°C, 45–50% at 60°C and 60–70% at 75°C in contrast to that in grapefruit juice. Detailed kinetics of combined pressure and temperature stability of ascorbic acid in different buffer (pH 4, 7 and 8) systems and real products (squeezed orange and tomato juices) have been carried out by Van den Broeck and coworkers (1998). At 850 MPa and 50°C for 1 hour, no ascorbic acid loss was observed. The high pressure/thermal degradation of ascorbic acid at 850 MPa and 65–80°C followed a first order reaction. The rate of ascorbic acid degradation at 850 MPa increased with increasing temperature from 65 to 80°C indicating that pressure and temperature act synergistically. Ascorbic acid in tomato juice was more stable than in orange juice. It was also reported that temperature dependence of ascorbic acid degradation (z value) was independent of the pressure level. Based on this study, it can be concluded that ascorbic acid is unstable at high pressure (850 MPa) in combination with high temperature (65–80°C). 21.5.2 Vitamin A and carotene The effect of high pressure treatment on carotene stability has been studied in carrots and in mixed juices. Based on the available literature data, we can conclude that high pressure treatment does not affect (or affects only slightly) the carotene content in food products. a- and b-carotene contents in carrot puree were only slightly affected by pressure exposure at 600 MPa and 75°C for 40 min (Tauscher, 1998). Similar findings have also been reported by de Ancos and coworkers (2000) showing that carotene loss in carrot homogenates and carrot paste 440 The nutrition handbook for food processors
High pressure processing 441 was maximally 5% under pressure condition of 600 MPa/75 C/40 min In orange lemon and carrot mixed juice, high pressure(500 and 800 MPa/room tempera ture/5 min) did not affect or only slightly affected the carotenoid content and during storage at 4C: the carotenoid content in the pressure treated juice remained constant for 21 days(Fernandez Garcia et al, 2001) In addition, high pressure treatment can affect the extraction yield of carotenoids. Studies on persimmon fruit purees showed that high pressure treat- ment could increase the extraction yield of carotenoids between 9 and 27%e.g Rojo Brillante cultivars(50 and 300 MPa/25C/15 min) and Sharon cultivars(50 and 400MPa/25C/15 min). The increase in extraction yield of carotene (40% higher) was also found in pressurised carrot homogenate(600 MPa/25C/10 min) (de Ncos et al, 2000) Pressure stability of retinol and vitamin A has been studied in buffer systems In the model systems studied, pressure treatment could induce degradation of vitamin A. For example, pressures up to 400-600 MPa significantly induced retinol (in 100% ethanol solution) degradation. Degradation up to 45% was obtained after 5 minutes exposure to 600 MPa combined with temperatures at 40 60 and 75C Pressure and temperature degradation of retinol followed a second order reaction. Another study on vitamin A acetate(in 100%o ethanol solution) showed that degradation of vitamin A acetate was more pronounced by increas ing pressure and temperature. About half of the vitamin A acetate concentration could be retained by pressure treatment at different pressure/temperature/time combinations. i.e. 650MPa/70 C/15 minutes and 600 MPa/259C/40 minutes. At 90C, complete degradation was observed after 2-16 minutes(pressure up to 600MPa). No effect of oxygen was noticed on retinol and vitamin A acetate degradation(Butz and Tauscher, 1997; Kubel et al, 1997; Tauscher, 1999) However, findings on retinol pressure stability in real food products differ from those obtained in model systems. In egg white and egg yolk, the initial retinol content can be preserved by pressure treatment from 400 up to 1000 MPa at 5C for 30 minutes(Hayashi et al, 1989) 21.5.3 Vitamins b. e and K The stability of vitamins B, E and K towards pressure treatment has been studied in model systems and food products In food model systems, high pressure(200, 400, 600MPa) treatments at 20C for 30 minutes have no significant effect on vitamin B1(thiamine)and B6(pyridoxal)(Sancho et al, 1999). Studies on the pressure effect on vitamin K showed that small quantities of m-and Diels-Alder products were formed after 3 hours at 650 MPa and 70C(Tauscher, 1999) In cow's milk, high pressure(400 MPa/room temperature/30 minutes)did not alter the content of vitamin B, and B,(pyridoxamine and pyridoxal)(Sierra et al, 2000). The thiamine content in pork meat was not affected by high pressure (100-250MPa/20C/10 minutes)even after long exposure time of 18h at 600 MPa and 20oC(Bognar et al, 1993). However, under extreme conditions of
was maximally 5% under pressure condition of 600 MPa/75°C/40 min. In orange, lemon and carrot mixed juice, high pressure (500 and 800 MPa/room temperature/5 min) did not affect or only slightly affected the carotenoid content and during storage at 4°C; the carotenoid content in the pressure treated juice remained constant for 21 days (Fernández Garcia et al, 2001). In addition, high pressure treatment can affect the extraction yield of carotenoids. Studies on persimmon fruit purées showed that high pressure treatment could increase the extraction yield of carotenoids between 9 and 27% e.g. Rojo Brillante cultivars (50 and 300 MPa/25°C/15 min) and Sharon cultivars (50 and 400 MPa/25°C/15 min). The increase in extraction yield of carotene (40% higher) was also found in pressurised carrot homogenate (600 MPa/25°C/10 min) (de Ancos et al, 2000). Pressure stability of retinol and vitamin A has been studied in buffer systems. In the model systems studied, pressure treatment could induce degradation of vitamin A. For example, pressures up to 400–600 MPa significantly induced retinol (in 100% ethanol solution) degradation. Degradation up to 45% was obtained after 5 minutes exposure to 600 MPa combined with temperatures at 40, 60 and 75°C. Pressure and temperature degradation of retinol followed a second order reaction. Another study on vitamin A acetate (in 100% ethanol solution) showed that degradation of vitamin A acetate was more pronounced by increasing pressure and temperature. About half of the vitamin A acetate concentration could be retained by pressure treatment at different pressure/temperature/time combinations, i.e. 650 MPa/70°C/15 minutes and 600 MPa/25°C/40 minutes. At 90°C, complete degradation was observed after 2–16 minutes (pressure up to 600 MPa). No effect of oxygen was noticed on retinol and vitamin A acetate degradation (Butz and Tauscher, 1997; Kübel et al, 1997; Tauscher, 1999). However, findings on retinol pressure stability in real food products differ from those obtained in model systems. In egg white and egg yolk, the initial retinol content can be preserved by pressure treatment from 400 up to 1000 MPa at 25°C for 30 minutes (Hayashi et al, 1989). 21.5.3 Vitamins B, E and K The stability of vitamins B, E and K towards pressure treatment has been studied in model systems and food products. In food model systems, high pressure (200, 400, 600 MPa) treatments at 20°C for 30 minutes have no significant effect on vitamin B1 (thiamine) and B6 (pyridoxal) (Sancho et al, 1999). Studies on the pressure effect on vitamin K1 showed that small quantities of m- and p-isomeric Diels–Alder products were formed after 3 hours at 650 MPa and 70°C (Tauscher, 1999). In cow’s milk, high pressure (400 MPa/room temperature/30 minutes) did not alter the content of vitamin B1 and B6 (pyridoxamine and pyridoxal) (Sierra et al, 2000). The thiamine content in pork meat was not affected by high pressure (100–250 MPa/20°C/10 minutes) even after long exposure time of 18 h at 600 MPa and 20°C (Bognar et al, 1993). However, under extreme conditions of High pressure processing 441
442 The nutrition handbook for food processors high temperature(100oC)combined with 600MPa, almost 50%o of the thiamine in pork meat was degraded within 15 min. Moreover, riboflavin in pork meat was only slightly affected (less than 20%) after pressure treatment at 600 MPa for 15 minutes combined with temperatures between 25 and 100oC (Tauscher, 1998) Heat-sensitive vitamin derivatives in egg white and/or egg yolk, i.e. riboflavin, folic acid, a-tocopherol and thiamine did not change during pressure treatment from 400 up to 1000 MPa at 25C for 30 minutes(Hayashi et al, 1989) It can be concluded that high pressure treatment has little effect on the vitamin content of food products. However, at extreme conditions of high pressure com- bined with high temperature for a long treatment time period, vitamin degrada- tion is observed. Regarding the use of high pressure in industrial applications, an optimised pressure/temperature/time combination must be chosen to obtain limited vitamin destruction within the constraints of the target microbial inacti- vation. For example, a mild pressure and temperature treatment can be developed equivalent to the conventional pasteurisation processes in order to keep the vitamin content in food products while inactivating vegetative microbial cells When spore inactivation is targeted, combined high pressure thermal treatments are needed and these treatments will affect nutrients. It is still an open question whether equivalent conventional thermal and new high pressure processes used or spore inactivation lead to improved vitamin retention. The available data suggest positive effects but more research is needed 21.6 Effect of high pressure on lipids The most interesting effect of high pressure on lipids in foods is the influence on the solid-liquid phase transition, e.g. a reversible shift of 16.C per 100 MPa for milk fat, coconut fat and lard( Buchheim et al, 1999). With respect to the nutri tional value of lipids, the effect of high pressure on lipid oxidation and hydroly sis in food products is of importance. Lipid oxidation is a major cause of food quality deterioration, impairing both flavour and nutritional values (related to health risks, e.g. development of both coronary heart disease and cancer). Effect of high pressure on lipids has been reported by many authors and the available literature shows that pressure could induce lipid oxidation especially in fish and meat products but did not, or only slightly, affect lipid hydrolysis. For example, pressures up to 1000MPa and 80oC did not affect the hydrolysis of tripalmitin and lecithin. Therefore, no fat/oil hydrolysis is expected to occur under condi- tions relevant for food processing(e.g 600MPa/60 C/time less than 30 minutes) (saacs and Thornton-Allen, 1998) Pressure induced lipid oxidation has been studied in different model systems and food products. In model systems, pressures up to 600 MPa and temperatures up to 40oC (less than 1 hour) had no effect on the main unsaturated fatty acid in milk, i.e. oleic acid. Linoleic acid oxidation was accelerated by exposure to pres sure treatments of less than one hour, but the effect was relatively small(about 10% oxidation)(Butz et al, 1999). Increasing pressure(100 up to 600 MPa and
high temperature (100°C) combined with 600 MPa, almost 50% of the thiamine in pork meat was degraded within 15 min. Moreover, riboflavin in pork meat was only slightly affected (less than 20%) after pressure treatment at 600 MPa for 15 minutes combined with temperatures between 25 and 100°C (Tauscher, 1998). Heat-sensitive vitamin derivatives in egg white and/or egg yolk, i.e. riboflavin, folic acid, a-tocopherol and thiamine did not change during pressure treatment from 400 up to 1000 MPa at 25°C for 30 minutes (Hayashi et al, 1989). It can be concluded that high pressure treatment has little effect on the vitamin content of food products. However, at extreme conditions of high pressure combined with high temperature for a long treatment time period, vitamin degradation is observed. Regarding the use of high pressure in industrial applications, an optimised pressure/temperature/time combination must be chosen to obtain limited vitamin destruction within the constraints of the target microbial inactivation. For example, a mild pressure and temperature treatment can be developed equivalent to the conventional pasteurisation processes in order to keep the vitamin content in food products while inactivating vegetative microbial cells. When spore inactivation is targeted, combined high pressure thermal treatments are needed and these treatments will affect nutrients. It is still an open question whether equivalent conventional thermal and new high pressure processes used for spore inactivation lead to improved vitamin retention. The available data suggest positive effects but more research is needed. 21.6 Effect of high pressure on lipids The most interesting effect of high pressure on lipids in foods is the influence on the solid–liquid phase transition, e.g. a reversible shift of 16°C per 100 MPa for milk fat, coconut fat and lard (Buchheim et al, 1999). With respect to the nutritional value of lipids, the effect of high pressure on lipid oxidation and hydrolysis in food products is of importance. Lipid oxidation is a major cause of food quality deterioration, impairing both flavour and nutritional values (related to health risks, e.g. development of both coronary heart disease and cancer). Effect of high pressure on lipids has been reported by many authors and the available literature shows that pressure could induce lipid oxidation especially in fish and meat products but did not, or only slightly, affect lipid hydrolysis. For example, pressures up to 1000 MPa and 80°C did not affect the hydrolysis of tripalmitin and lecithin. Therefore, no fat/oil hydrolysis is expected to occur under conditions relevant for food processing (e.g. 600 MPa/60°C/time less than 30 minutes) (Isaacs and Thornton-Allen, 1998). Pressure induced lipid oxidation has been studied in different model systems and food products. In model systems, pressures up to 600 MPa and temperatures up to 40°C (less than 1 hour) had no effect on the main unsaturated fatty acid in milk, i.e. oleic acid. Linoleic acid oxidation was accelerated by exposure to pressure treatments of less than one hour, but the effect was relatively small (about 10% oxidation) (Butz et al, 1999). Increasing pressure (100 up to 600 MPa and 442 The nutrition handbook for food processors
