Effect of soybean-to-water ratios on physicochemical properties, proximate composition, and sensory characteristics of soy yogurt

Soy yogurt is made by fermenting aqueous extracts obtained from soybeans and is a type of plant-based dairy alternative withtextural sensory qualities and an ability to host viable lactic acid bacteria for long-term storage. This study aims to improve the quality of soy yogurt by investigating the effects of different soybean-to-water ratios on the physicochemical parameters, proximate compositions, and sensory properties of soy yogurt (SY). The shelf-life of selected SY was also determined at 4℃ for 14 days.

During soymilk making process, different ratios of soybeans and water (1:5, 1:6, and 1:7 w/v) under constant cooking conditions (100℃ for 20 min) were investigated. After cooking, the soymilk samples were cooled down, inoculated with commercial yogurt culture (L.acidophilus, Bifidobacterium amimalis, L. bulgaricus, and S. thermophilus), and
incubated at 42℃ for 12h to obtain the SY for further analysis and sensory evaluation.

The ratios of soybeans and water significantly (p<0.05) affected the pH, total acidity, total soluble solids, water holder capacity, and consistency of SY ranged between 4.13 and 4.39, between 0.26 and 0.59%, between 8.63 and 15.33 ᵒBrix, between 37.83 and 73.68%, and between 7.83 and 18.15 cm/30s. The moisture, ash, protein, lipid, and carbohydrate content of SY had no significant
difference (p>0.05) between 83.22 and 89.39%, between 0.02 and 0.23%, between 2.81 and 4.94%, between 0.19 and 0.37%, and between 5.68 -and13.67%. However, the sensory evaluation of SY obtained from a 1:5 soybean-to-water ratio received the highest overall acceptance score of 6.38, compared to the SY using 1:6 and 1:7 ratios. The SY can also be safely consumed for up to 14 days of storage at 4℃ based on pH, total acidity, total soluble solids, and non-detectable microbial counts. Therefore, this
study revealed that selecting a suitable amount of water in soymilk processing had a significant effect on nutritional, functional, and sensory qualities in SY with a long shelf life.