Effect of freezing treatment of soybean on soymilk nutritional components, protein digestibility, and functional components.

Soymilk is a popular beverage in many countries owing to its nutrition and health effects. To increase household consumption of soymilk, instant soybeans were developed by freezing and subsequent drying pretreatment, which overcome the time-consuming need of soaking during soymilk preparation for home making. However, compared with the traditional soymilk making, the nutritional quality and functional properties of this soymilk made from the soybean by direct grinding in water without soaking are not clear yet. Soymilk made from untreated soybeans, soaked soybeans, and soaking, freezing, and air-drying soybeans (FADTS) were compared on their properties including nutritional components, in vitro protein digestibility, and functional components. It was found that FADTS was the best at extracting lipid and Ca, good at extracting of protein, carbohydrate, oligosaccharides, Fe, phytic acids, and tannins, and in producing soymilks with highest in vitro protein digestibility. The soluble protein and protein digestibility of FADTS (4 day) increased significantly from 44.4% and 78.5% of control to 56.2% and 85.0%, respectively. Soymilk from 4 days FADTS contained similar protein content and higher Fe content (4.40 mg/kg) compared to soaked sample (3.82 mg/kg). The results revealed that FADTS performed better at producing soymilk than untreated and soaked soybeans.