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, Bj, 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 (200-500MPa/30°C/1min) 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 900MPa/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 600MPa for 10-30min (Kimura, 1992; Kimura et al, 1994). In freshly squeezed citrus juices, high pressures up to 600 MPa at 23°C for 10min 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 400MPa/20°C/30min (88.68% of the initial content in fresh sample) and in guava purée, high pressure (400 and 600MPa/15min) 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 20°C for 30min 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 (500MPa/room temperature/3min) 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 (500-700MPa/50-60°C/60-90 s) was 20-45% higher than in heat treated juice (98°C/10s) during storage at 4 and 8°C for 20 weeks (Parish, 1997).

Studies on guava purée showed that different high pressure processes have a

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

Pokka Corp. (stopped c2000-2001)

Wakayama Food Ind.

Nisshin fine foods

Kibun (stopped in 1995)

Yaizu fisheries (test market only)

Chiyonosono

Fruit based products (pH < 4.5); jams (apple, kiwi, strawberry); jellies; purées; yoghurts; sauces

Grapefruit juice

Mandarin juice (winter season only) (only «20% of HP juice in final juice mix)

Fuji chiku mutterham Raw pork ham

'Shiokara' and raw scallops

Fish sausages, terrines and 'pudding'

Sugar impregnated tropical fruits (kept 50-200 MPa at -18°C without freezing). For sorbet and ice cream

400MPa /

Pasteurisation, improved gelation, faster sugar penetration; limiting residual pectinmethylesterase activity

Reduced bitterness

Reduced odor of dimethyl sulphide; reduced thermal degradation of methyl methionine sulphoxide; replace first thermal pasteurisation (after juice extraction) and final pasteurisation before packing: 90 °C, 3min

Faster sugar penetration and water removal

Faster maturation (reduced from 2 weeks to 3 hours); faster tenderisation by internal proteases, improved water retention and shelf life

Microbial sanitation, tenderisation, control of autolysis by endogenous proteases

Gelation, microbial sanitation, good texture of raw HP gel

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) Continued

Company

Product

P/T/time combination

Role of HP

QP corp

Ehime co. Echigo seika

Takansi

Pon (test market in 2000)

Ice nucleating bacteria (for fruit juice and milk)

Japanese mandarin juice

Moci rice cake, Yomogi fresh aromatic herbs, hypoallergenic precooked rice, convenience packs of boiled rice

Fruit juice

Orange juice

400-600MPa, 10min, 45 or 70°C

Inactivation of Xanthomonas, no loss of ice nucleating properties

Cold pasteurisation

Microbial reduction, fresh flavour and taste, enhances rice porosity and salt extraction of allergenic proteins

Cold pasteurisation

EUROPE Pampryl (France)

Espuna (Spain)

Orchard House Foods Ltd. (UK) (since July 2001)

Fruit juice (orange, grape fruit, citrus, mixed fruit juice)

Deli-style processed meats (ham)

Squeezed orange juice

400MPa, room temperature

400-500MPa, few minutes, room temperature

500MPa, room temperature

Inactivation of micro flora (up to 106CFU/g), partial inactivation of pectinmethylesterase

Inactivation of micro flora (especially yeast) and enzyme, keeping natural taste

THE UNITED STATES Avomex

Motivatit, Nisbet Oyster Co, Joey Oyster

Hannah International Foods

Avocado paste (guacamole, chipotle sauce, salsa) and pieces

Oysters Hummus

300-400MPa, room temperature, 10 minutes

Microorganism inactivation, polyphenoloxidase inactivation, chilled process

Microorganism inactivation, keeping raw taste and flavour, no change in shape and size o r.

/ indicates no detailed information available.

different influence on the stability of vitamin C during storage. The ascorbic acid content in untreated and pressurised (400MPa/room temperature/15min) guava puree started to decline respectively after 10 and 20 days whereas that in heated (88-90°C/24s) and (600MPa/room temperature/15min) 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 (400MPa/20°C/30min) 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 40min 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 (600MPa 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 850MPa and 50°C for 1 hour, no ascorbic acid loss was observed. The high pressure/thermal degradation of ascorbic acid at 850MPa and 65-80°C followed a first order reaction. The rate of ascorbic acid degradation at 850MPa 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 (850MPa) 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 40min (Tauscher, 1998). Similar findings have also been reported by de Ancos and co-workers (2000) showing that carotene loss in carrot homogenates and carrot paste was maximally 5% under pressure condition of 600MPa/75°C/40min. In orange, lemon and carrot mixed juice, high pressure (500 and 800MPa/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 300MPa/25°C/15min) and Sharon cultivars (50 and 400MPa/25°C/15min). The increase in extraction yield of carotene (40% higher) was also found in pressurised carrot homogenate (600MPa/25°C/10min) (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 600MPa 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. 650MPa/70°C/15 minutes and 600MPa/25°C/40 minutes. At 90°C, 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; 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).

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 20°C for 30 minutes have no significant effect on vitamin Bj (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,

In cow's milk, high pressure (400MPa/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 (100-250MPa/20°C/10 minutes) even after long exposure time of 18h at 600 MPa and 20°C (Bognar et al, 1993). However, under extreme conditions of high temperature (100°C) combined with 600MPa, 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 600MPa 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 1000MPa 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 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 for spore inactivation lead to improved vitamin retention. The available data suggest positive effects but more research is needed.

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