Processing of soybean meal influences in vitro kinetics of protein digestion in the small intestine

The study investigated the processing effect on in vitro kinetics of protein digestion of soybean meal - non-processed (SBM) and after thermo-mechanical, enzyme-facilitated processing (TEP); and of TEP vs fermented soy protein (FSP) vs soy protein concentrate (SPC). Samples (n=72) were incubated in triplicate sequentially with pepsin at pH 3.5 for 1.5 h (stomach phase) and with pancreatin and bile extract at pH 6.8 for 0 to 6 h (small intestine phase). Protein was classified into CPfast, CPslow and CPresistant corresponding to digested CP within the first 0.5 h, from 0.5 to 4 h and after 4 h, respectively. The TEP increased digested CP by 13% (P<0.001) and CPfast by 24% (P=0.039), reduced CPresistant by 11% (P=0.002) and tended to decrease CPslow by 49% (P=0.060) compared with non-processed SBM. In vitro digestibility of CP was greater (P<0.001) in TEP than in FSP and SPC at each time point. The kinetic equation showed that TEP tended to have greater maximum protein digestion rate than FSP (0.70 vs 0.24%/h; P=0.058). The CPresistant content was lower in TEP than in SPC (141 vs 280 g/kg DM; P=0.022). Therefore, protein would be digested faster with less chance to reach the large intestine in TEP than SPC and FSP. In conclusion, processing of SBM enhanced the in vitro kinetics of protein digestion in small intestine. Thermo-mechanical, enzyme-facilitated processing of SBM enhanced in vitro protein digestion kinetics to a greater extent than fermentation and extensive extraction.