Abstract: In the present study, the digestion characteristics of the common soy products soy protein isolate (SPI), microwaved soybean, boiled soybean, soy milk, calcium chloride-coagulated tofu, and magnesium chloride-coagulated tofu were evaluated using the standardized INFOGEST static (INFOGEST 2.0) in vitro digestion system. The gastrointestinal digests were taken at different time points to determine the intact proteins, molecular mass distribution, free amino group concentration and particle size distribution. The different processing methods promoted the digestion of soy protein. Proteins in the five soy products were partly digested by simulated gastric fluid. During intestinal digestion, soybean proteins are all thoroughly digested into short peptides. Compared with SPI, the free amino group concentration of microwaved soybean and boiled soybean significantly increased, while the digestion of microwaved soy protein was more complete; the digestibility of soy protein was lower in soy milk than in calcium chloride-coagulated tofu and magnesium chloride-coagulated tofu, but there was no significant difference between the two types of tofu. In summary, the results of this study are helpful for better understanding the digestibility of proteins in soy products obtained by different processing methods, which will provide a reference for the consumption of dietary plant proteins.

Key words: INFOGEST 2.0; common soybean products; soybean protein; processing methods