Study On Storage And Preservation Technology Of Fresh Walnut Kernel

Walnut is a nutritious dried fruit with high economic value.In recent years,with the implementation of the national poverty alleviation strategy,large areas of walnut have been planted and put into production,resulting in a sharp decline in the price of dried fruit,walnut products to find a way to ensure the interests of fruit farmers is imperative.Fresh walnut meat in the catering industry annual demand increased sharply,the market price suddenly.In this study,fresh walnut shelled as raw material was used to obtain a set of fresh walnut meat preservation technology by studying its peeling process,preservative formula,packaging method and storage conditions,providing technical support for prolonging the shelf life of fresh walnut meat and better developing fresh walnut meat products.(1)Using response surface methodology(RSM)to optimize the peeling process of walnut kernels.The effects of sodium hydroxide concentration,ultrasonic time,ultrasonic temperature and ultrasonic time on the score of peeling difficulty and sensory score of fresh walnut kernel were studied.Through single factor test and response surface test optimization,the optimal technological conditions of walnut kernel peeling were obtained as follows:The concentration of sodium hydroxide was 0.4%,the ultrasonic temperature was 47?,the ultrasonic time was5min and the ultrasonic power was 377W.At this time,the peeling difficulty score of fresh walnut meat was 6.6 points.The adjustment and determination coefficient R~2=0.9864indicated that the regression equation fitted the experiment well and the regression effect was good.(2)Effects of different antioxidants on the quality of walnut kernelsThe influence of different antioxidants on fresh walnuts storage quality test results show that:compared with control group,different antioxidant processing of the unriped walnuts have certain effect,ascorbic acid with citric acid+L-cysteine experimental group treated fresh walnuts the off color,acid value,peroxide value,significantly lower than the other group,and inhibit polyphenol oxidase and lipase activity,keep the catalase is highly active.(3)Effects of different packing materials on walnut qualityThe effects of different packing materials and packing methods on the storage quality of fresh walnut kernels the experimental results show that aluminum foil film packing materials are more airtight than PE packing materials,which can effectively delay the water loss of fresh walnut kernels,the increase of color difference and the process of oxidation and rancidity.Compared with sealed packing and vacuum packing,vacuum-de-oxygenated packing can better maintain the sensory quality and color of fresh walnut meat.At the end of storage,the walnut meat packed with aluminum foil film vacuum deaerating has the best quality and preservation effect.(4)Effects of different storage conditions on the quality of walnut kernelThe effects of different storage conditions on the storage quality of fresh walnut kernels the results showed that the storage effect of fresh walnut kernels under frozen storage condition was better than that under normal temperature storage and cold storage,and the storage period of fresh walnut kernels could be extended to 75 days within the range of the experiment.At the end of storage,the sensory score,water content and fat content of walnut kernel stored in frozen storage condition were significantly higher than those in other storage conditions,and the color difference,acid value and peroxide value of walnut kernel were kept at a lower level,the activity of polyphenol oxidase and lipase were inhibited,and the catalase activity was kept at a higher level.By using low-field NMR instrument that:in the early stage of storage,the semi-binding water moved faster,and the water consumed by the respiration of fresh walnut kernel supplemented the free water through the semi-binding water,so the water content in the early stage of storage decreased more slowly.In the later stage of storage,the natural oxidation speed of walnut kernel was accelerated,and the water evaporation was more,indicating that the semi-binding water in the walnut kernel was migrating to free water with the extension of storage time,thus resulting in the decline of walnut kernel quality.(5)Shelf life prediction and quality standard establishment of walnut kernelBy using Arrhenius formula,a kinetic model was established for the sensory score,acid value and peroxide value in the storage process of fresh walnut kernels.The correlation coefficient R~2 of the regression equation was all greater than 0.9,indicating that the regression equation fitted the test well and could predict the shelf-life of fresh walnut kernels.Compared with the predicted shelf life,the error is within 10%.Therefore,the dynamic model can predict the shelf-life of fresh walnut meat relatively accurately.By referring to the requirements of relevant standards and combining with the actual situation of the product,the quality standard of fresh walnut meat was established.