Solid-state fermentation alters the fate of red kidney bean protein during buccal and gastrointestinal digestion: Relationship with cotyledon cell wall integrity.

The relationship between legume cotyledon cell wall and macromolecular nutrient digestibility has attracted increased attention. In this study, the effect of solid-state fermentation by Rhizopus oligosporus RT-3 on the digestibility of red kidney bean protein and its relationship with cotyledon cell integrity were investigated. Buccal digestion and gastrointestinal digestion were performed to compare the fate of protein between unfermented (F0) and fermented samples. Results showed a remarkable disruption in cotyledon cell integrity at the late fermentation period, and it was accompanied by a possible migration/degradation of protein matrix. Buccal and gastrointestinal digestion barely affected cell wall integrity at F0 but notably disintegrated cell morphology at 29 h of fermentation (F29). As this fermentation time, gastrointestinal digestion resulted in higher contents of soluble proteins, peptides, and free amino acids by 1.4-, 1.8-, and 2.5-fold, respectively. Therefore, solid-state fermentation facilitated the structural breakdown of cotyledon cell walls, thereby further improving protein digestibility.