Preparation And Characterization Of Hydrolyzed Protein From Walnut Meal

Walnut is a kind of tree nut with high nutritional value,Nowadays,China's walnut planting area,harvest area and walnut yield are the highest in the world,in addition to domestic sales of fresh food and part of the export abroad,is mainly processed into walnut milk,walnut oil,walnut meal and other products.In the process of producing walnut oil,it produced a large number of by-products of walnut meal,which contain a large amount of protein in these meals,many walnut processing enterprises use walnut meal as feed or directly discarded,this causes the waste of protein resources in walnut.In order to make full use of walnut cake and increase its added value,in this study,the basic nutrients of walnut meal which is a by-product of walnut oil extraction were determined first,enzymatic hydrolysis of walnut meal was used to extract protein hydrolysate directly,then the hydrolytic enzymes were screened and the factors affecting the enzymatic hydrolysis were systematically discussed,finally,the characteristics of walnut meal with different degree of hydrolysis were studied by limiting enzymatic hydrolysis.The results show that:(1)Walnut meal was used as raw material to determine its basic nutritional components: In walnut meal,including 61.94% protein content,12.79% moisture content,9.18% fat content and 7.82% ash content.The kinds and contents of amino acids in walnut meal were determined.The results showed that there were 17 kinds of amino acids in walnut meal.The contents of arginine,serine,glutamate and aspartic acid were high,and the nutritive components were rich.It can be used as a good source of plant protein.(2)The process of enzymatic hydrolysis of hydrolyzed protein of walnut meal was studied,and five proteases were screened for alkaline protease,neutral protease,papain,compound protease and compound flavor protease.The hydrolysis degree and protein extraction rate were used as the index to screen the neutral protease.On the basis of determining the hydrolytic enzyme as neutral protease,the optimum process for extracting hydrolyzed protein from enzymatic walnut meal was determined by single factor test and orthogonal test.The enzyme was added to 3000 u/g,pH8.0,the hydrolysis temperature was 55,the ratio of material to liquid was 1:12,and the time of enzymatic hydrolysis was 45 min.(3)For the hydrolysis protein of walnut meal can be better used in food processing,the functional properties of hydrolyzed protein with different degree of hydrolysis are studied.The results showed that the nitrogen content index of hydrolyzed protein was higher than that of walnut meal,and the nitrogen content index of hydrolyzed protein was above 70%.The oil absorption of hydrolyzed protein was higher than that of walnut meal,and when the degree of hydrolysis was 3,the oil absorption ability of the hydrolyzed protein was the highest,reaching 4.172 g/g.When pH is 3,the emulsifying property of walnut meal is higher than that of hydrolytic protein,and the best emulsification stability is hydrolytic protein with 4 hydrolysis degree.When pH is 5,the emulsification of walnut meal is lower than that of hydrolysate,and the best emulsification stability is hydrolytic protein with the degree of hydrolysis of 4,and the stability of the walnut meal is less than that of the hydrolytic protein;pH is 7 when the emulsification is 7.The emulsification of the hydrolysate with 1 hydrolysate was the highest,the best emulsifying stability was walnut meal;when the pH was 9,the hydrolysate protein with the hydrolysis degree of 2 was the highest,and the best emulsifying stability was the hydrolysate protein with the degree of hydrolysis of 1.SDS-PAEG gel electrophoresis showed that the electrophoretic bands of walnut meal protein were mainly 48~63 kDa,and the bands of hydrolytic protein with hydrolysis degree of 1~7 were mainly between 25~35 kDa.17 kinds of amino acids of hydrolyzed protein were detected,and the amino acids of higher content were consistent with walnut meal.In this study,the resources of walnut meal were utilized,and the added value was improved,which provided theoretical support for the application of hydrolysate protein of walnut meal in food processing.