Soaking Time and Temprature on Condensed Tannin and Phytic Acid of Sybean Products

Abstract

To enrich the diet, soybean plays great role by reducing protein malnutrition by substituting animal protein. However, the major problems in raw soybeans are off flavor and anti-nutritional factors. Processing also affect nutritional value unless optimum processing methods are used. Thus, this investigation was carried out to evaluate the effect of soaking temperature and time on anti-nutritional factors (phytic acid and condensed tannins) made from soybean variety AFGAT (Glycine max). Two soaking temperatures hot water (40^°C) and ambient temperature (25^°C) and three soaking times (8, 12 and 16 hrs) were considered in the experiment. The study revealed that soaking time and temperature had significantly (p<0.05) affected on anti-nutritional factors. Soy flour condensed tannin was significantly (p<0.05) higher (0.23 mg CE g ^-1) at 16 hrs soaking time with 40^°C. The values exhibited reduction in condensed tannin (0.03±0.01 mg CE g ^-1) soaking at 8 hrs for 40^°C. The soaking time and temperature showed reduction in condensed tannins from 0.29 mg CE g ^-1 (raw) to 0.02 mg CE g ^-1. Higher (9.17mg g^-1) soy flour phytic acid was observed at 12 hrs soaking time with 40^°C. Increased in the level of phytic acid from 4.11 mg g^-1 (raw) to maximum 9.17mg g^-1(soaked for 12 hr at 40^°C) in flour was observed. Soy milk condensed tannin was also affected by soaking time and temperature and ranged from 0.07 to 0.24 mg CE g ^-1 for soybean soaked for 8 hrs at 25^°C and 40^°C and for soybean soaked for 16 hrs at 25^°C, respectively. The higher soy milk phytic acid was 8.31 mg g^-1for soybean soaked for 8 hrs at 25^°C. The phytic acid was decreasing when the soaking time increases at lower temperature. In conclusion the anti-nutritional factors of soybean flour and milk were influenced by soaking time and temperature. The result obtained suggests that good quality soybean flour and soybean milk can be obtained from soybean soaked for 8 hrs at 40^◦C.

Keywords: Anti-nutritional factors, Soaking time, temperature, Soybean, Soy flour, Soy milk