Protein bioaccessibility of soymilk and soymilk curd prepared with two Lactobacillus plantarum strains as assessed by in vitro gastrointestinal digestion

Abstract The current study was conducted to compare the protein bioaccessibility of soymilk and two soymilk curds generated by fermentation with Lactobacillus plantarum B1-6 and Lactobacillus plantarum 70810. Soluble protein content, degree of hydrolysis, and electrophoretic patterns were monitored during in vitro gastrointestinal digestion of the soymilk and curds. Soluble protein content of digested soymilk was 2.0–2.6 times higher than that of digested curds as measured by the Bradford assay. The degree of hydrolysis was 1.6 times higher in digested soymilk than in digested soymilk curds as determined by the ortho -phthalaldehyde (OPA) method. Electrophoretic data showed that soymilk curds had slower protein digestion rates during simulated gastric and intestinal digestion. The soy protein 7S α′, 7S α and 11S acidic subunits and a peptide of 28 kDa were observed even after simulated intestinal digestion. The different degradation profiles suggest that the soymilk curd hinders enzymatic hydrolysis during simulated gastrointestinal digestion. Industrial relevance Soymilk curd is a popular food in East and Southeast Asian countries. Lactic acid fermentation is an emerging technology to form soymilk curds that creates a product with improved functional and probiotic properties. The purpose of the present study was to compare protein degradation profiles of soymilk curds produced by fermentation with Lactobacillus plantarum B1-6 and 70810, and of soymilk using an in vitro gastrointestinal digestion system. Results of the study will expand the knowledge base of the effects of this novel coagulation technology on the nutritional characteristics, especially protein bioaccessibility of soymilk curds and thus would be expected to provide fundamental information in the future application of the emerging coagulation technology using lactic acid bacteria.