Chemical composition and antioxidant activity of some fermented vegetable juices compared to fresh vegetable juices

Abstract

The aims of this study were to evaluate (1) the conversion rate of nitrate to nitrite in red pepper and tomato juices, and (2) the total polyphenols content (TPC), total carotenoid content (TCC) and antioxidant activity (AA) of fresh compared to fermented juices obtained from red pepper (Capsicum annuum L.) and tomato (Solanum lycopersicum L.). Red pepper and tomato juices were obtained from frozen fruits and fermentation was made in the presence of Staphylococcus xylosus ATCC strain 29971 (108 CFU/mL). The nitrate and nitrite concentration (ppm) was determined from 6 to 6 hours for 30 hours. For nitrate and nitrite determination, colorimetric methods were used. After 30 hours of incubation at 37°C, it was found a conversion rate of nitrate to nitrite of 85.10 % for red pepper, and 81.87 % for tomato. Fermented juices of red pepper and tomato showed similar conversion yield of nitrate to nitrite. The TPC, TCC and AA were determined for fresh and fermented juices using colorimetric methods. TPC, expressed as mg gallic acid equivalents/100 mL (mg GAE/100 mL) and TCC, expressed as mg β carotene equivalents/100 g wet weight (mg β-CarE/100g WW), varied considerably between unfermented and fermented sterilized juices, with highest concentrations in the unfermented pepper and tomato juices (42.34 ± 2.82 and 57.92 ± 3.86, respectively) for polyphenols, and (31.85 ± 2.12 and 61.76 ± 4.12, respectively) for carotenoids. AA was expressed as % Inhibition of DPPH•. After fermentation, the antioxidant activity decreased for both juices, the decrease rate was 39.50% for red pepper and 32.18% tomato juice.