| Our country walnut production is huge and walnut germplasm resources are rich,walnut has very high nutritional value often eat walnuts on consumers cardiovascular,sleep and so on have beneficial effects.With the development of the nut industry,the losses caused by oxidative rancidity of nuts are difficult to measure.Walnuts are especially susceptible to oxidative damage during storage due to their high oil content,which leads to rages and spoilage.This irreversible oxidation process has the greatest impact on the storage of peeled walnut kernel products.Because the antioxidant activity in the walnut is mainly concentrated in the walnut shell,walnut green peel,walnut seed coat.At present,the common method to extend the shelf life of walnut products is to exogenously add chemically synthesized antioxidants or find new packaging materials,which increases the cost of walnut products and is not good for consumers.The aim of this study was to develop the antioxidant potential of walnut proteins through enzymatic preparation and provide theoretical basis for prolonging the storage of peeled walnut kernels.At the same time,the antioxidant peptide obtained by enzymatic hydrolysis was separated by chromatography technology and its antioxidant mechanism was studied.It is expected to provide new ideas and theoretical basis for extending the shelf life of nutroasted food.The main research contents and conclusions are as follows:(1)Using peeling walnut kernel as raw material and antioxidant capacity of hydrolysate as index,single factor experiments were used to study the effects of substrate concentration,enzyme addition,hydrolysis temperature and hydrolysis time on the antioxidant activity of hydrolysate.On this basis,orthogonal experiments were used to optimize the enzymatic hydrolysis process conditions,and the optimal hydrolysis process was determined as: The hydrolysis was performed at 45 ℃ for 20 min with 12%enzyme and 40% substrate.Under the optimal hydrolysis process,the superoxide anion free radical scavenging rate was 63.21%,the hydroxyl free radical scavenging rate was 97.66%,and the reducing power was188.68%.(2)The effect of enzymatic hydrolysis on the oxidation stability of walnut kernels was studied by Rancimat lipid stability tester and the oxidation quality index of walnut kernels during accelerated storage.The results showed that after the walnut kernels were hydrolyzed by complex protease(trypsin),the walnut oil obtained by cold solvent extraction obtained obtained by cold solvent extraction had a longer oxidation induction time and Q10 index,and the oxidation free energy also increased from 59.896 KJ/mol to 78.103 KJ/mol.Surface enzymatic hydrolysis effectively improved the oxidation stability of walnut kernels.The peroxide value of the control group was always higher than that of the sample group during the storage process.Taking the peroxide value as the index and the kinetic equation of oil oxidation,the shelf life of walnut kernels after surface enzymatic hydrolysis at 20 ℃ was prolonged by 56.96 d compared with the control group.The results of this study provide a theoretical and technical basis for the efficient antioxidant and flavor quality maintenance of walnut kernels.(3)Walnut protein was prepared using peeled walnut kernels as substrate and the enzymatic digestion process was optimised by combining antioxidant parameters.The enzymatic digest was purified by Smartdex G-50 gel chromatography to obtain four fractions,from which the most active fraction was selected.The amino acid sequences of the fractions with the highest antioxidant activity were identified by LC-MS/MS and the resulting sequences were screened by computer virtual screening to obtain three peptides.The three peptides were molecularly docked to the crystal structure of the lipoxygenase protein,and the peptide with the lowest binding energy,R.AGIQFPVG.R,was selected with a binding energy of-5.24 kcal/mol.R can spontaneously bind to lipoxygenase under natural conditions to form a stable structure,and the binding site indicates that the peptide delays the acidification of walnut oil mainly through noncompetitive inhibition.In conclusion,R.AGIQFPVG.R is considered to be the main bearer of the antioxidant activity of the D-4 fraction.. |
