Physicochemical, Textural and Sensory Characteristics of Probiotic Soy Yogurt Prepared from Germinated Soybean

Soymilk prepared from germinated soybean [Glycine max (L.) Merrill] with different hypocotyl lengths was fermented at 42 °C for approx. 4 h to produce soy yogurt (sogurt) with the combined probiotics of Lactobacillus helveticus B02, Streptococcus thermophilus IFFI 6038 and Lactobacillus bulgaricus AS1.1482. The physicochemical, textural and sensory characteristics of the fermented products were subsequently analyzed. Results showed that sogurt prepared from germinated soybean with the length of hypocotyls of 3 cm displayed lower pH and higher titratable acidity, and appeared to be more acceptable by the trained panel than sogurts prepared from soybean with hypocotyl length of 0 and 6 cm (p<0.05). Texture profile analysis demonstrated that the hardness of sogurts significantly decreased (from 26.71 to 16.89 g), while the adhesiveness significantly increased (from –71.77 to –31.94 g·s) as hypocotyl length increased (p<0.05). Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) profile of soymilk demonstrated that the a’ and a subunits of b-conglycinin (7S) and the acidic chains of glycinin (11S) were gradually degraded, which may be partly responsible for the decline of water holding capacity and the amelioration of textural properties of the germinated soy yogurt. The total concentration of free amino acids obtained by high-performance liquid chromatography (HPLC) was 515.78 mg/mL in the soymilk from ungerminated soybean (S0), while it reached 847.44 and 880.75 mg/mL from soybean with 3-cm (S3) and 6-cm (S6) hypocotyls, respectively. Some of the increased levels of free amino acids may account for the improvement of flavour and reproduction of lactic acid bacteria. It could be concluded that, with appropriate germination, the physicochemical and textural properties as well as sensory characteristics of sogurt could be improved significantly.