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 a21.5 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, B1, B2, E and folic acid and the decrease of vitamin C in pressurised orange juice is neg￾ligible 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 pres￾sure 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) 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 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 treat￾ment. 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