Preparation Of Peanut Antioxidant Peptide By Ultrasonic-assisted Enzymatic Hydrolysis

According to researches at home and abroad，the peanut protein hydrolysate has a goodantioxidant activity．Ultrasonic cavitation can promote the process of protein hydrolysis.Peanut meal left50percent of protein after oil expression. However at present the peanutmeal is mainly used of the forage. In this study, we used the peanut meal by low-temperatureof discarding solvent as material，extract peanut-protein-isolate(PPI) from the material, inorder to prepare peanut peptide by enzymatic hydrolysis PPI. And thereby research thestructure and antioxidant activity of the peanut peptide.In this paper， we studied the preparation of antioxidant peanut peptides byultrasonic-assisted enzymatic hydrolysis respectively using Flavourzyme，Alcalase and thecombination of Flavourzyme and Alcalase. Selecting the hydrolysis degree as evaluationindex，we studied the effects of ultrasonic pretreatment，water-curing treatment，andultrasonic-assisted enzyme treatment on the preparation of the peanut peptides. The resultsshowed that the hydrolysis degree of ultrasonic pretreatment was larger than those ofwater-curing treatment and ultrasonic-assisted enzyme treatment under the same conditions.The hydrolysis degree reached the highest value29.81%after ultrasonic pretreatment andAlcalase hydrolysis for8hours. With the increase of the hydrolysis degree in the hydrolysisprocess，the reducing power of the peanut peptides increased first and then decreased. Thepeanut peptides prepared by ultrasonic pretreatment and Alcalase hydrolysis had the largestreducing power，and the antioxidant ability was equal to that of Vc with the concentration of50.92μg/mL.Colour chromatism analysis showed that ultrasonic can reduced peanut protein yellowdegree, had little impact on peanut peptide by the same enzymatic reaction. The yellowdegree of Alcalase hydrolysis was higher than Flavourzyme hydrolysis. The analyse of-SHand-S-S-showed that the ultrasonic pretreatment lead to a significant decrease of the amountof disulfide bonds and an increase of the amount of-SH．After ultrasonic, the total-SH ofpeanut protein reduced; The molecular weight distribution (MWD) of the peanut peptidesshowed that ultrasonic can decrease peptide of>5000D from4.31%to3.75%, while canincrease peptide of <1000D from73.36%to75.70%. Amino acid analysis results showed that ultrasonic can increase the amount of Pro from3.14%to3.82%, and can increase the amountof Arg from12.26%to12.48%. Infrared Spectroscopy analysis, showed that fitting analysisindicated that spectra of amideⅠshowd that structure of peanut protein β-turn accounted for alarger proportion. After ultrasonic, the amount of β-sheet increased, no rules curly decreased.Compared with water-curing treatment，the amount of β-sheet the peanut peptides prepared byultrasonic pretreatment and Alcalase hydrolysis increased from33.08%to63.69%, α-helixdecreased from14.64%to4.21%. The fluorescence spectra of peanut protein and peanutpeptides excited to exhibit characteristic absorbency of Trp residues and Tyr residuces at280nm. Compared with peanut protein, the largest emission peak of PPI solution’ s fluorescencespect rashifted in red shift, indicating that the environment of the Trp residues in PPI hadaltered with ultrasound treatment.Determination of antioxidant activity showed that: Using ultrafiltration, we prepared5kinds of peanut peptides, We did several experiments include reducing power, DPPH radicalscavenging rate, OH radical scavenging rate and O—2radical scavenging rate. The antioxidantactivity of5kinds of peanut peptides increased with the concentration of peanut peptides. Thesize of antioxidant activity for5kinds of peanut peptides was <1kD、1~3kD、3~5kD、>10kDand5~10kD. Peanut peptides (<1kD) had the highest antioxidant activity. Meanwhile, theantioxidant activity of peanut peptides mainly concentrated in the range of low molecularweights.