Impact of Thermal Processing Parameters During Black Soymilk Extraction and Pasteurization on Key Bioactive Compounds and Antioxidant Capacity

Heat treatments applied to soymilk during extraction and pasteurization may affect, among other aspects, the content of bioactive compounds. In this study, we identified favorable processing conditions during black soymilk production (extraction and pasteurization) to preserve key bioactive compounds and the antioxidant capacity (AC) of the black soybean. Temperature (80-98°C) and time (5-15min), conditions for black soymilk extraction from (unpeeled) milled beans followed a 22 factorial design. Anthocyanins and isoflavones were analyzed by HPLC-PDA-reverse phase system. AC was measured by ORAC and DPPH assays. Results were treated by ANOVA and Fisher test at p ≤ 0.05. Soymilk samples were treated by batch pasteurization (98°C for 10 and 5min, respectively) and ultra-high-temperature (UHT) (134°C for 6 sec). The best pasteurization parameters for high flavonoid contents and AC were chosen for the preparation of a chocolate-soymilk-beverage which was tested for sensory acceptability. Changes in temperature and time affected significantly the content of anthocyanins and AC. The best soymilk extraction and pasteurization conditions for anthocyanin and AC preservation were 80°C for 5min and 98°C for 5min, respectively, with 80% anthocyanins, 100% isoflavones, and 100% AC recovery compared to non-pasteurized control. The developed functional black soymilk beverage presented similar acceptance to a commercial organic yellow soy-based beverage.