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 afterpossible 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 (i) microorganism inactivation; (ii) modification of bio￾polymers 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 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 inactivating 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-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), pressure￾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). Besides, 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 40°C 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 434 The nutrition handbook for food processors