Assessment of dynamic digestion fate of soy protein gel induced by lactic acid bacteria: A protein digestomics research

Food matrix plays an important role in regulating macronutrient digestibility. In this study, lactic acid bacteria (LAB)-fermented soy protein isolates (FSPIs) were prepared at a series of concentration (0.2%–5.0%, w/v). FSPIs with varied structures were obtained and tested in an in vitro dynamic gastrointestinal model. Then, a comparative digestomics research was conducted. Results demonstrated that the lowest gelation concentration of soy protein during LAB fermentation was 1.9% (w/v). The FSPIs showed structures ranging from a loosely stacked layer (non-gel, NG) to a denser gel network with varied hardness (weak gel, WG; medium gel, MG; and firm gel, FG) when the protein concentration was adjusted. The protein profile of gastrointestinal digestates demonstrated higher soluble protein and peptide in FSPI gels compared with FSPI-NG. FSPI gel digestates were predominantly promoted in glycinin G1 and the β-conglycinin α subunit. The change was dynamic between FSPI gels with varied structures. Weaker gels (FSPI-WG and FSPI-MG) facilitated the hydrolysis of glycinin G1/G4 and β-conglycinin α/β subunits at early and medium digestions (0–30 min). In comparison, the firmer gel (FSPI-FG) showed a postponed but more extensive promotion of the degradation of glycinin G1/G2 and β-conglycinin α subunits at the late digestion (180 min). The spatial structures of glycinin G1 and β-conglycinin α subunits demonstrated variations in seven and eight regions, respectively. Glycinin's region 6 (Y374–R388) and β-conglycinin's region 7 (L491–T519), which are located at the interior of the 3D structure, were the key regions contributing to the discrepancies.