Optimization Of The Preparation Process Of The Wheat Oligopeptides And Analysis Of The Antioxidant Ability

Wheat oligopeptides(WOP), as the gluten hydrolysate, exhibit healthcare function. It possesses significant value for the manufacture of WOP health food to investigate the hydrolysis of wheat gluten to increase the hydrolysis ratio of WOP and yield. In this paper, the wheat gluten was hydrolyzed by various enzymes to compare the hydrolysis ratio. The trypsin-alcalase hydrolysis system was the best one and the parameters were further optimized. Moreover, the amino acid composition, structure characteristics, antioxidant ability of the WOP were investigated. The contents and results were as the follows:(1) Optimization of the preparation of the wheat peptides by double enzyme method. Wheat gluten was chose as the raw material(75% protein), which is hydrolyzed by the papain, neutral protease, flavourzyme, trypsin, alcalase, with the degree of hydrolysis 3.7%, 5.2%, 13.7%,17.4% and 18.3%, respectively. Complex enzyme hydrolysis experiments were conducted by three enzymes with the high degree of hydrolysis. The trypsin-alcalase hydrolysis system showed the highest degree of hydrolysis 32.56%, which was further optimized by orthogonal experiment. The parameters of the trypsin-alcalase hydrolysis system were as the follows,hydrolysis temperature 40℃ and 65℃, pH 10 and 8, the addition of enzyme 7% and 7%,hydrolysis time 4 h and 3 h for the trypsin and alcalase, respectively, with the final degree of complex enzyme hydrolysis 37.72%. The molecular weight of the hydrolysate was mostly between 1374~445 Da with the ratio of 52.03% according to the peak area, which was determined by the HPLC.(2) The desalination of the wheat protein hydrolysate by series combination adsorbent resins. The series combination of the DA201-C macroporous resin and HW-40 S gel resin exhibited the good desalting effect on the hydrolysate according to the result of test. The parameters of the desalting system were investigated by the single factor and response surface experiment with the indicators of desalinization ratio and yield of peptide. The optimal conditions of the desalination were as follows, loading solution concentration 31 mg/m L, loading flow rate 2 mL/min, eluent flow rate 2 mL/min, 80% alcohol as the eluent. The ratios of desalination and recovery peptide were 98.24% and 95.5%, respectively. The hydrolysate was purified by the 1000 u ultrafiltration membrane to obtain the small peptide mixture less than1000 u.(3) Structure analysis, antioxidant ability of the WOP. The WOP conformed to the national standards of the food additives according to the analysis of the physical-chemical indexes. The contents of the histidine, serine, tyrosine, glutamic acid, valine, phenylalanine, methionine were higher than that of the crude protein. There was positive correlation between the enhancement of the hydrophobic amino acid and the antioxidant activity. There were characteristic absorptionpeaks in the 1290~1330 cm-1 and 1695~1660 cm-1 on the basis of the structural analysis by FTIR, which indicate the presence of α-helix and β-sheet with the major of β-sheet. The antioxidant activity of the WOP was determined by the ORAC, which showed the ability of scavenging lipid free radical. The ORAC value of the WOP was higher than that of glutamine as the concentration ≥1.5 mmol/L with the highest of 14.38 times, which demonstrated the significant antioxidant activity of the WOP.