The evaluation of structural changes, in vitro digestibility and digestates composition of protein in soybean meal during high-temperature storage

This study aimed to investigate the changes in protein structure, in vitro digestibility, and digestates composition in soybean meal (SBM) during simulated summer high-temperature storage. The SBM was stored at 35 °C for 0, 1, 2, 4, 8, and 16 weeks. The carbonyl and free thiol content, zeta-potential, secondary structure, and protein in vitro digestibility of the protein in SBM were determined. The amino acid content, molecular weight distribution, and peptide composition of the in vitro digestion products of SBM stored for 0, 1, 4, and 16 weeks were measured. The results showed that the protein carbonyl content started to increase from the first week, which increased by 44.19 % at 16th week, while the free sulfhydryl content decreased by 26.76 %. The zeta-potential of the protein in SBM was reduced and the thermal stability was enhanced at the first week. Cysteine, methionine, lysine, and arginine were oxidatively modified during high-temperature storage. The protein in vitro digestibility decreased by 4.81 % at 16th storage week. In addition, the proportion of small molecules (molecular weight <500 Da) was reduced in the digestion products, and the peptide composition of the digestion products from SBM stored for different durations varied. The peptide GDHTSQITK was identified as a potential oxidation marker. This study indicated that high-temperature storage results in protein oxidation of SBM, and causes a decrease in protein in vitro digestibility and free amino acids content in digestion products of SBM. This study was recommended that the storage time not exceed two weeks. • High temperature storage led to protein oxidation of soybean meal. • Protein oxidation of soybean meal affected protein in vitro digestibility. • Cysteine, methionine, lysine, and arginine were key oxidation sites in soybean meal. • The peptide GDHTSQITK was identified as a potential oxidation marker for soybean meal. • Recommended storage time under high temperature is not more than 2 weeks.