Further processing of soybean meal using thermomechanical and enzyme-facilitation modified secondary protein structure, in-vitro protein digestion kinetics and nutritive value in broiler chickens

Further processing of protein feedstuffs, such as conventional soybean meal (CSBM), may improve their nutritive value. This study evaluated chemical attributes, in-vitro protein digestion kinetics, apparent (AID) and standardized (SID) ileal digestibility of amino acids (AA), and apparent metabolizable energy (AME) in CSBM subjected to thermomechanical and enzyme-facilitated processing (PSBM). For the in vitro digestion, samples were sequentially incubated in triplicate, with pepsin at pH 2.5 for 0 and 0.5 h (gizzard phase), then with pancreatin and bile extract for 0, 0.5, 1, 1.5, 2, 2.5 and 3 h (intestinal phase, pH 6.5). A total of 180 one-day-old Ross 708 male chicks were fed a commercial starter diet until day 13 (n = 6). On day 14, birds were assigned to one of three diets: a nitrogen-free diet (NFD), or test ingredients containing 20 % crude protein (CP) from either CSBM or PSBM as the sole source of AA. Titanium dioxide (0.5 %) was included as an indigestible marker. Excreta were collected between days 17 and 20, and ileal digesta on day 21. Fourier-transform infrared spectroscopy revealed structural shifts (P < 0.05) in PSBM compared to SBM, including increased β-sheets, emergence of 3_10-helix, and reduced random coils and intramolecular aggregates. Compared to CSBM, PSBM had a higher proportion of fast-digestible protein (P < 0.001), representing a 21 % increase, and lower proportions of both slow-digestible (P = 0.001) and resistant protein fractions (P = 0.002). Compared to CSBM, PSBM had greater AID of CP, Lys, Met, and Thr (P = 0.001). The SID of Lys, His, and Val and total AA were greater in PSBM (P < 0.05) than CSBM. The PSBM tended to have greater AME than CSBM (P = 0.079). In conclusion, PSBM had modified secondary protein structure resulting in enhanced in vitro protein digestion kinetics profile, and improved digestibility of nutrients in broiler chickens.