Study On The Antioxidative Peptides From Fermented Soybean Protein Meal By Lactobacillus Plantarum Lp6

Antioxidant compounds in food such as phenolic compounds played various roles as health promoting factors (e.g., cancer and cardiovascular disease), antimicrobial agents; flavor active compounds, colorants precursors, and colloidal stability affecting factors as well as chelating agents. Fermented foods such as soy products have been in existence for thousands of years and received attention as sources of many effective antioxidants. In this study, soybean protein meal was subjected to solid state fermentation with Lactobacillus plantarum Lp6 either in the presence or absence of a protease.The solid-state fermentation of soybean protein meal (SPM) by Lactobacillus plantarum Lp6 was studied to evaluate the influence of the soluble starch, acid protease and time, on degree of hydrolysis (DH) and viable cell counts (VCC). The fermented soybean protein meal (FSPM) was optimized for maximum DH and VCC using response surface methodology (RSM). The optimum conditions determined were the following: soluble starch (0.4 g/g of SPM), acid protease (0.1 g/g of SPM), and time (66 h). The optimized values were 22.58% and 9.08 (log CFU/g) for DH and VCC respectively. Fermentation using the optimized process conditions increased the amount of low molecular weight peptides (< 20 kDa) compared to SPM with high molecular weight polypeptides (> 97.4 kDa). The protein content (60.15%) of FSPM increased following fermentation of SPM. The free amino acids profile (0.32 to 8.03 g/100 g protein) and protein solubility (29.33% to 38.35%) increased significantly (P< 0.01) during fermentation due to the hydrolytic actions of L. plantarum Lp6 and acid protease. FSPM had the highest in vitro trypsin digestibilityFermented soybean protein meal hydrolysate (FSPMH) was fractionated by gel filtration on Sephadex G-15. The fractions obtained were subjected to various antioxidant assays, amino acid and molecular weight determinations. Among the seven fractions, the highest antioxidant activity was found in fraction F2, with significant differences (P< 0.01) 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, hydroxyl radicals (·OH) scavenging and Cu2+ chelating activity. F2 exhibited scavenging of DPPH (59.43%),·OH (72.80%) and 44.47% Cu2+ chelating activity. All other fractions showed variable activities in different assays. Amino acid analyses of F2 fraction with the strongest antioxidant activity also had the highest percentage of related antioxidative amino acids content (Histidine 3.46, Serine 5.78, Valine 4.08 and Lysine 11.49 g/100 g protein) compared with the other six fractions. The molecular weight distribution of F2 was found to vary from 170 to 1500 Da.The fraction F2 which showed the highest antioxidant properties was subjected to reverse phase high performance liquid chromatography (RP-HPLC) for purification, the resultant peaks were collected separately as fractions and subsequently subjected to DPPH radical scavenging and Cu2+ chelating tests. The amino acid sequences of identified peptides were then determined by liquid chromatography/tandem mass spectrometry (LC-MS/MS). The RP-HPLC fraction P1 showed stronger DPPH radical scavenging ability and possessed relatively strong Cu2+ chelation ability compared to 5 other fractions (P2, P3, P4, P5 and P6). The identified amino acid sequences of P1 contained Histidine.