Preparation Of Cocoon Polypeptides And Study On Its Antioxidative Activity

The antioxidant peptide, as a kind of bioactive peptides, more and more was applied in the area of food to prevent oxidation and used as function factor in the area of cosmetic. Now using accessory substances produced by processing of agricultural materials to propare bioactive peptide is becoming the hot investigation in research and development.In our country, sericulture was major industry which producing a considerable amount of accessory substances such as cocoon. Cocoon protein was a kind of high quality, native, full value protein. The protein content of the cocoon was as high as 96%. In this dissertation, the cocoon polypeptide hydrolysates were obtained by hydrolyzing cocoon protein with proteinase, and then purified by ultra filtration. At the same time, the antioxidative activity of hydrolysates was studied. The principal contents are as follows:1. The reaction conditions of the ferric reducing/antioxidant power (FRAP) assay, which included pH value, reaction time were studied. The optimal pH value and reaction time were 3.4 and 10 min respectively respectively.2. The pretreatment method of raw materials was determined. The raw materials were heat treated at 100℃for 2 h. Multifect neutral was selected as the best hydrolyzing enzyme in five kinds of protein enzymes by assessing the total antioxidation capacity of hydrolysates.3. The optimum conditions are determined by only-factor and orthogonal experiments, which was: 60℃, pH 6.5, enzyme concentration 10%(w/w), substrate concentration 3.3g/100ML and reaction time 210min. Under this condition, the total antioxidation capacity(A₅₉₅) of hydrolysates which was diluted five times was 1.795, DH was 4.2% and Solids was 9.2mg/mL.4. The hydrolysates prepared under the optimum parameters with Multifect Neutral were filtrated by ultra filtration using MW 10kDa and 3kDa membranes respectively. A₅₉₅ of original hydrolysates, MW>10 kDa, MW<10kDa, MW 3～10kDa, MW< 3kDa peptides filtrate is 1.810, 0.593, 1.605, 0.783, 1.423. Cocoon antioxidant peptides powders of MW<3kDa were prepared by freeze-drying method. TCA of cocoon antioxidant peptides was 1.773, compared with that of BHT,Vc 2.618, 2.206, all at the concentation of 1.5mg/mL, which meant TCA of 1.5g cocoon antioxidant peptides was was equivalent to that of 0.4g BHT or 0.7g Vc. 5. UV-Vis, IR, CE were utilized to analyse cocoon antioxidant peptides. The results suggested that the characteristic absorption wavelengh of MW<3kDa antioxidant peptides was 274 nm. MW<3kDa antioxidant peptides consists of more than 10 components. The secondary structures contained mostα-helix, phenyl and hydroxyl.