Study On The Functional Properties Of Enzymatic Hydrolysates Of Walnut Protein Isolate

Walnut is widely distributed all the world and it is rich in nutrients,with high health function and economic value.The planting area and yield of walnut in China rank the first in the world.Excepts for exports,dried or as fresh food,walnuts are mainly processed into products,such as walnut oil,walnut milk,walnut powder,snack foods and so on.The extraction of high value of walnut oil is the main way of walnut processing,and the walnut meal after squeezed contains 50%?60%protein.As we all know,walnut protein is one of the high quality resource of plant protein,especially riched with Arg,Glu and Asp.However,due to different extraction methods of walnut oil,lacking of peeling and other pre-treatment process,the color of walnut meal is always deep with poor quality,poor function,which restricts the application of walnut meal in the field of food processing and food ingredients.As a result,most of the walnut meal is discarded or only for feeding.Not only cause the waste of resources,but also pollute the environment.In this study,the effects of enzymatic modification on the functional and antioxidant activities of walnut protein isolate were studied in this paper.During experiments,the main conclusions were as follows:1.The protein of walnut meal defatted powder was extracted by alkali soluble acid precipitation method.The protein content of walnut protein was 88.91%.2.The optimal process of alkaline protease digestion of walnut protein isolate was obtained by L9(34)orthogonal test.The results showed that optimum hydrolysis condition was as follows:pH 9.0,enzyme 4.0%,substrate concentration 5.0%and temperature 55.0?.3.The hydrophobicity of the walnut protein isolate decreased with the increase of the degree of hydrolysis,surface hydrophobicity index of the three enzymatic hydrolysates were 610,460 and 435 respectively,which indicated that the enzymatic hydrolysis could decrease the molecular groups of walnut protein isolate.4.When the hydrolysis degree was from 2.20%to 7.93%,the solubility of walnut protein isolate could be improved obviously.The solubility of walnut protein isolate increased from 3.87%to 55.99%at pH 4.5,the solubility of the hydrolysates were more than 50%at different pH,and the solubility increased with the increase of the degree of hydrolysis.Enzymatic modification technology can improve the solubility of walnut protein isolate,broaden the applicable pH range of walnut protein,and lay the foundation for food ingredients and processing industry.5.The emulsification property of the walnut protein isolate increased with the decrease or increase of the pH value,and the change trend was consistent with that of the walnut protein isolate.DH 7.93%of the hydrolysate at pH 10 had the best emulsifying and emulsifying stability,86.76 m2/g and 77.01%,respectively.6.Foaming capacity and foam stability of walnut protein isolate and its enzymatic hydrolysates were influenced by pH.When deviatied from the isoelectric point,the foam stability of hydrolysates were better.Enzymatic modification improved foaming capacity of walnut protein isolate.The foaming capacity of DH2.20%hydrolysate reached 143.33%at pH 2.0.The foaming stability of DH7.93%hydrolysate reached 80.01%at pH 2.0.7.Study on antioxidant capacity of walnut protein hydrolysates showed that the enzymatic hydrolysate of walnut meal had some ability of reducing ability,and the reducing power of the hydrolysate was higher than that of walnut meal,and higher than that of BHT.In the three free radical scavenging models,walnut protein isolate hydrolysate has the ability to scavenge DPPH free radical,superoxide anion radical,hydroxyl radical,and has obvious effect.