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 8-conglycinin alpha 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 8-conglycinin alpha/8 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 8-conglycinin alpha subunits at the late digestion (180 min). The spatial structures of glycinin G1 and 8-conglycinin alpha subunits demonstrated variations in seven and eight regions, respectively. Glycinin's region 6 (Y374-R388) and 8-con-glycinin's region 7 (L491-T519), which are located at the interior of the 3D structure, were the key regions contributing to the discrepancies.

Automated summary

Food matrix is important in regulating macronutrient digestibility. In this study, lactic acid bacteria (LAB)-fermented soy protein isolates (FSPIs) with varied concentrations were prepared and tested in an in vitro gastrointestinal model. A comparative digestomics research was conducted to analyze their structures and protein profiles. Results showed that FSPIs had varied structures and promoted the hydrolysis of different protein subunits at different stages of digestion. The spatial structures of glycinin G1 and 8-conglycinin alpha subunits played key roles in these discrepancies.