Evaluation of protein digestibility of fermented soybeans and changes in biochemical characteristics of digested fractions

Abstract

This study evaluated the protein digestibility of fermented soybeans inoculated with Bacillus subtilis var. natto using a simulated in vitro gastrointestinal digestion model. It was found that the total trichloroacetic acid (TCA)-soluble peptide yield increased when the digestion stage progressed and compared to those of fermented soybeans before digestion. Most high molecular weight proteins disappeared after 4 h of digestion. All essential amino acids were found to increase remarkably (∼4%), especially Arg. Antioxidant amino acids such as Tyr, His and Phe were also found to increase. The highest antioxidant activity was found in the fractions after digestion corresponding to the antioxidant amino acids obtained. An increase in nitric oxide inhibition (9–29%) and a decrease in egg albumin denaturation activity (73–48%) were observed. Fermentation improved the protein digestibility of boiled soybeans by 45% and may benefit human health due to an improvement in essential amino acids and bioactivity through digestion.

Keywords

• Natto
• Processing
• Amino acids
• TCA-soluble peptides
• In vitro anti-inflammatory