Preparation Of Walnut Protein Optimization And Determination Of Antioxidant Activity

Walnut is a genus of Juglandaceae Juglans. Walnut, whose edible parts is rich in nutrients, contains protein, unsaturated fatty acids, vitamin E, flavonoids, folic acid, polyphenols and other physiologically active ingredients, so that it has a good health care function.Given that the walnut oil contains essential fatty acids and contains up to 90% of the unsaturated fatty acids, people have successfully developed and launched high-quality walnut oil on the market. However, most manufacturers treat the degreasing walnut as feed processing, and failure to fully exploit its proper value at present. If it is made into walnuts peptides, that can not only turn waste into treasure, but also add a new peptide products for the healthcare market.Firstly, this paper compared the composition of different varieties of walnuts conming from different origin, to choose the best varieties of walnut meal protein as raw materials for the walnut peptide research. This paper used kjeldahl determination, DNS, soxhlet extraction method to determine the total protein, total sugar and fat content of different origin of five varieties of walnut kernel. In terms of protein content, the protein content of U.S. Howard, Xinjiang Xinguang Fenyang ZhonglinNo.1, Gansu Zhouzhigenian, Yunnan Niangqing walnut was 17.46%,19.3%,19.41%,17.61%,16.84%. So this paper choosed Fenyang Zhonglin No.1, whose protein content is the highest as raw materials for the walnut peptide.This paper used enzyme technology, optimized the preparation conditions of walnut peptide. It selected the pH, temperature, liquid-solid ratio, stirring time as factors. On the basis of single factor test, it selected the optimum mixing time as 60 min. Optimizing other factors by response surface software, it got the best alkali-soluble conditions, whose maximum extraction rate is 96.6485%, pH value is 10.67, temperature is 57.17℃ and the liquid-solid ratio is 89.99 mL/g. Verification tests and predicted values was closer, it showed that the model was correct. Then it did the univariate tests,that showed the optimal pH value of acid sinking for walnut protein is 5.Then, this paper optimized the conditions of the hydrolysis of walnut protein by neutral protease. This paper took enzyme concentration, substrate concentration, pH, temperature, hydrolysis time as influencing factors, optimized the hydrolysis condition by using response surface method. In this model, this paper got the optimal solution,that the degree of hydrolysis could reach 11.9986% when hydrolysis time was 3.5h, enzyme concentration was 9999.99U/g, substrate concentration was 10%, pH was 7.21, temperature was 50.07℃. The average of three validation tests for the degree of hydrolysis was 11.7277%, which was close to the predicted value. Walnut peptide was expected to less than 2000 Da in terms of the average molecular weight.According to the optimized conditions,this paper extracted the protein of walnut, dealt the protein with enzymatic hydrolysis, got through ultrafiltration membrane (2000 Da 5000Da), concentrated and got the product spray-dried to obtain two samples of walnut polypeptides:samples 1 and samples 2. In vitro antioxidant function test, this paper detected the scavenging capacity of hydroxyl radical, the scavenging capacity of superoxide radical and the reducing power of the two samples. The results showed that:both of the two samples have antioxidant activity, and the three antioxidant activity are consistent. When one of the antioxidant effect is strong, the other two have a strong antioxidant effect. Compared with the 2 samples, samples 1 had a stronger antioxidant capacity. On this basis, conducted the antioxidation in vivo in mice with samples 1, According to the method for determination of antioxidant capacity from "The handbook of inspection and evaluation for functional food" to determine the activity of glutathione peroxidase in blood and level of malonaldehyde in liver tissues and blood. Results showed that determination results of glutathione peroxidase and MDA assay in experimental animals were positive, so that the determination results of antioxidant test for walnut peptides were positive in animal experiments.This article chose the best raw material of the preparation of walnut peptide, optimized the extraction conditions of walnut protein and the preparation of walnut polypeptide, set up the production process of the preparation of walnut peptide by walnut pulp, and got a new walnut peptide product. Walnut peptide was proved to have good antioxidant activity by the biochemical experiment in vitro and the animal experiment in vivo. The experimental data lays the foundation for the application of walnut polypeptide.