Preparation And Application Of Antioxidant Peptides From Walnut Grown In Xinjiang, China

Walnut is one of the main economic forest trees which with a long history of cultivation in Xinjiang China. Walnut protein content accounts for 14% to 17% in Walnut kernel, its digestion rate can reach to 85%, and contains 8 essential amino acids ,so walnut is a good source of protein. Walnut products on the market at present are single, deep processing products are rarely.Walnut oil production factories now have amounted to dozens ,a lot of skim walnut meals are used as fodder、fertilizer or discarded, environment polluted with waste discharge, its added value is lower. It’s reported that the protein in the walnut residue reaches up to 53.89%. So the development and utilization of defatted walnut meals have extremely practical value and broad prospects. The preparation of walnut peptides using skim walnut meal as raw materials was deliberated in this research:the ultrasound-assisted was used to prepare walnut protein, the response surface method was used to optimize and determine the optimum process conditions; the SDS-polyacrylamide gel electrophoresis was used to determine the molecular weight distribution of walnut protein; enzyme and aspergillus fermentation methods were used in the preparation of walnut peptides respectively, with the DPPH radical scavenging rate、the absorbance value as the index, the response surface method was used to optimize and determine the optimum process conditions; barrier separation was used to study the molecular weight distribution of walnut peptides with the antioxidant activity,and combined with chemical analysis method; the response surface method was used to optimize and determine the optimum process conditions of walnut peptide oral liquid, with sensory evaluation value as index, for skim walnut meal applications in food, medicine, daily chemical provided scientific basis and theoretical guidance.The preparation technology of walnut protein was observed in this paper.The method of ultrasound-assisted was used to process skim walnut meal, with protein leaching rate as an index, and response surface analysis method was applied to optimize the formular.The best preparation process parameters were as follows: ultrasonic time for 19min, ultrasonic temperature for 46℃, ratio of solution / material for 20, pH for 8.6.The molecular weight distribution of walnut protein was studied in this paper.The SDS-polyacrylamide gel electrophoresis was used to determine the molecular weight distribution of walnut protein, electrophoresis pattern showed that the molecular weight of walnut protein were mainly distributed in the 14.4 KDa～66.2 KDa.Preparation methods of walnut peptides were discussed in this paper.Enzyme method was used in the preparation of walnut peptides. With degree of hydrolysis as index, the alkaline protease was chose to hydrolyze walnut protein. Single-factor experiments and response surface analysis were adpoted to study the effect of [E]/[S], pH value and enzymolysis temperature on preparation of antioxidant peptide, with the DPPH radical scavenging rate as the index. According to the above results,the optimum enzymatic hydrolysis conditions for preparation of antioxidant peptides from Walnut protein using alkaline protease enzyme was obtained as follows:[E]/[S] 2.6%,pH 9,enzymolysis temperature 49℃,[S]2%, enzymolysis time 2 h. Under these conditions, the scavenging rate of DPPH radical was up to 69.85%.Aspergillus fermentation method was researched in this paper.Single-factor experiments and response surface analysis were used to study the effect on preparation of antioxidant peptide, with the absorbance value as the index, the optimum fermentation conditions for preparation of peptides from walnut meal using aspergillus was obtained as follows: the concentration of walnut meal 7%, pH6, inoculum 11%, proven experimental showed that under optimum conditions this peptide content of walnut was 22.33μg/mL.The molecular weight distribution of walnut peptides with the antioxidant activity were studied in this paper.Ultrafiltration was used in the purification of walnut protein hydrolysate, reductive force determination、removal ability with diphenyl generation bitter hydrazine base free radicals（DPPH·）、superoxide anion radical（02 -·）、hydroxyl radical（·OH） were used to discuss the antioxidant activity of various components in proteolytic walnuts from the angle of molecular weight distribution.The results showed that: the walnut protein peptide all represent strong antioxidant activity in four kinds of in vitro antioxidant model, and have more significant concentration-response relations; antioxidant activity of walnut protein hydrolysates has a certain relationship with the size of the molecular weight, reductive ability of MW <1 kDa were the strongest, MW>10 kDa showed the weakest reductive. Peptides with molecular weight of MW <1 kDa showed the strongest scavenging ability with DPPH·、·OH, 0₂^-·, while the molecular weight of MW>10 kDa showed the weakest scavenging ability with DPPH·,·OH), 0₂^-·.The optimum processing technology and formular of walnut peptide oral liquid were obtained with sensory evaluation value as index,and response surface analysis mathod was applied to optimize the formular .The best recipe process parameters were as follows: 2% of peptide, 8% of xylitol, 0.2% of malic acid, proven experimental confirmed that under optimum conditions the oral sensory evaluation of walnut peptide is 93.5.