| Bioactive peptides from soybean have attracted much attention in recent years. Soybeanpeptides have many advantages that can be easily digested and absorbed. Besides, they havemany bioactivities including antifatigue and reduce cholesterol.In this paper, the processing conditions of preparation of bioactive peptides by soyprotein isolate enzymolysis with commercial proteases and solid fermentation of soybeanmeal were systematically studied. Ultrafiltration, ion-exchange chromatography, and gelfiltration chromagraphy were applied to the separation of peptides. ESI-MS/MS was adoptedfor the identification of peptides. Moreover, the application of soybean peptides in tobaccofilters was also studied. Main results achieved in this research were as follows:With soy protein isolate as raw material, three commercial proteases (Alcalase, Neutrase,Pepsin) were used to prepare soybean peptides (CP) with antioxidant activity. The antioxidantcapacities (AOC) of enzymatic hydrolysates were evaluated by ORAC (oxyen radicalabsorbance capacity). The results showed that, in the appropriate enzymatic condition, theORAC value of the hydrolysate zymolysised by Alcalase, which was1910.48μmol Troloxequivalent/g Peptide,1611.91mg Glutathione equivalent/g Peptide, was the highest, that byNeutrase took the second place, and that of Pepsin was the lowest. At the same time, thesignificant correlation between ORAC value of soybean peptide and its DPPH radicalscavenging capacity was found.With defatted soybean and wheat bran as nitrogen source and carbon source forAspergillus oryzae, the koji-making conditions of Aspergillus oryzae were optimized, and theeffects of the ratio of material carbon and nitrogen (C/N), culture time and inoculum size tohydrolysis characteristics of koji and antioxidant activities of its hydrolysis products (FP)were studied. The results showed that the optimum koji-making conditions were as follows:C/N for1/5, culture time for44h, and inoculum size for0.05%(W/W). Under aboveconditions, the alkaline protease activity of koji was up to3109.85U/g and the effects of theaddition of soybean protein isolated or soybean protein extracted, pH, substrate proteinconcentration, and hydrolysis time on hydrolysis characteristics and antioxidant of itshydrolysis product (FP) were also studied. The results showed that the optimum hydrolysisconditions were as follows: pH for7, substrate protein concentration for8%, there was noneed to add nutrition, hydrolysis time for4h. Under above conditions, the ORAC value ofhydrolysis product was up to2130.22μmol Trolox equivalent/g Peptide, and the IC50ofDPPH was0.2975mg/mL, which indicated that the antioxidant capacity of FP was higer compared with the peptide product by commercial proteases enzymolysis (the ORAC value ofhydrolysis product was1910.48μmol Trolox equivalent/g Peptide and the IC50of DPPH was7.08mg/mL).Ultrafiltration, ion-exchange chromatography, and gel filtration chromagraphytechniques were performed to purify CP and FP. It was found that alkaline peptides hadgreater contributions to the antioxidant activities of CP and FP than acidic peptides or neutralpeptides. The peptides with molecular weight less than1,000Da was more important to theantioxidant activities of CP and FP. The purified peptide from CP was identified as Ser-Phe-Val (352.4Da) using RP-HPLC connected on-line to an electrospray ionization massspectrometry, and the purified peptide from FP was identified as Leu(Ile)-Tyr-His-Thr (531.9Da) using RP-HPLC connected on-line to an electrospray ionization mass spectrometry.Application of antioxidant peptide in tobacco filters was preliminary explored. Theoptimum conditions for the absorption of FP-V with glass beads were protein concentration4.0mg/mL, absorption temperature30oC and absorption time8h.The FP-V could stillmaintained78.24%of its original ORAC value and76.44%of its DPPH radicals scavengingactivity. This reached the application conditions of tobacco filters and provided theoreticalbasis for the application of cigarette filters. |
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