Study On The Extraction Process And Functional Properties Of Cottonseed Protein Isolates

The amino acid composition of Cottonseed protein is complete, have a good balance in essential amino acids composition compared with the FAO standard, and have a higher nutritional value. Cottonseed protein is not only an important source of feed protein, but human-edible high quality plant protein. In this thesis, we studied the extraction process and functional properties of cottonseed protein isolates; optimized the detection conditions of the cottonseed protein peptide obtained by enzymatic hydrolysis; compared the effect of peptide yield between conventional and microwave-assisted enzymatic hydrolysis method, optimized the microwave-assisted enzymatic hydrolysis conditions and studied the antioxidant activity of the hydrolysates. The results are as follows:1. The cottonseed protein isolate was prepared according to the Alkali-soluble extraction and acid precipitation method, the optimal conditions as follows:extraction pH11.0, temperature45℃, extracting time h, solid to liquid ratio of1:25. centrifuge and filter the extraction, adjust the supernatant to pH4.5for precipitation, than centrifugation and filtration, the precipitate was freeze-dried to get cottonseed protein isolate products. At these conditions, the rate was70.45%, protein content was96.97%, and the free gossypol content was45.85mg/kg. Cottonseed protein isolate’s water absorption, oil absorption, solubility, emulsification, emulsion stability, foaming capacity and foam stability were analyzed. We obtained that cottonseed protein isolate had good food functional properties, can be applied to food.2. The determination conditions of peptide molecular weight distribution of Cottonseed protein hydrolyzate were optimized. We choose the cytochrome C, Aprotinin, bacitracin, oxidized glutathione and reduced glutathione as a standard molecular weight substances, obtained the retention time and molecular weight relationship equation was Y=-4125.6X+45264, R2=0.9982, where Y is the molecular weight, X is the retention time.3. The optimal conditions for conventional enzymatic hydrolysis of crude cottonseed protein as follows:the first step, the substrate concentration5%, temperature60℃, the system pH8.0, the alkaline protease addition3%; the second step, the temperature of50℃, the system pH7.0, the flavour protease addition4%, enzymatic hydrolysis time4h. In this condition, the degree of hydrolysis of cottonseed protein was25.74%and the peptide yield was64.33%.4. Raw materials was pretreated by ultrasonic, microwave, ultrasonic and microwave three kinds of pretreatment methods, compared with the control group, pretreatment before microwave-assisted enzymatic hydrolysis can improve the yield of cottonseed protein peptide, ultrasonic and microwave pretreatment compared with the other two pretreatment, the difference is significant; compare with the natural pH pretreatment, adjusting the pH to8.0before pretreatment, can improved the peptide yield;5%of substrate concentration, the peptides yield was higher than the10%of substrate concentration; The use of alkaline protease combined with flavour protease, can got more peptide than only use the alkaline protease. 5. The optimal condition of microwave-assisted enzymatic hydrolysis of crude cottonseed protein through the response surface methodology was:substrate concentration5.06%, enzyme concentration5.83%, microwave power44.63W, hydrolysis time59.70min, pH8.0, temperature60℃.Under this condition, the peptide yield of crude cottonseed protein was58.39%.6. The optimal condition of microwave-assisted enzymatic hydrolysis of cottonseed protein isolate through the response surface methodology was:substrate concentration4.08%, neutral protease concentration14.45%, microwave power39.18W, the enzymatic hydrolysis time60min, pH7.0, temperature40℃. Under this condition, the peptide yield was79.82%. Ultrafiltration of the hydrolysates, Comparison of antioxidant capacity through DPPH radical, hydroxyl radical and superoxide anion radical scavenging capacity, results show that antioxidant capacity of the fraction1(<2kDa) is greater than the fraction2(2-5kDa) and mixtures.