Effects Of Different Frozen Conditions On Oxidation Resistance And Quality Of Fresh Walnuts

Compared with dried walnuts,fresh walnuts have relatively low fat content,high amino acid content and crisp taste.They are popular among consumers.However,due to their high water content and physiological characteristics,they are extremely susceptible to mildew and germination during storage and have short storage life.The current preservation technology cannot meet the long-term needs of the market.The frozen storage technology has been widely used in the preservation of fruits and vegetables due to its high efficiency and convenience,and has broad application prospects for the preservation of fresh walnuts.The research on the effect of frozen storage conditions on the oxidation resistance and quality of different fresh walnuts during the storage period was carried out by using'Xiangling'fresh walnuts as the test materials.The relationship between the antioxidant properties and quality of fresh walnuts under different frozen conditions was investigated.The suitable freezing conditions and best forms for long-term storage provide theoretical basis and technical support for the application of frozen technology for the annual supply of fresh walnuts.The main results were as follows:?1?The sensory quality of fresh walnuts was maintained better by the frozen storage.The seed coats of nuts and green fruits at-20? and-40? were still pale yellow and easy to peel off at 10 months.The walnut kernels had no odor,but the seed coat of the kernels were difficult to peel off.?2?The frozen storage could effectively maintain the high L*value and low?E*value of the seed coat in the fresh walnuts,and the preservation effect on the seed coat color of the nuts and the green fruits were more remarkable at-20?.?3?The frozen storage maintained the high SOD,CAT activity and DPPH clearance rate of nut kernels,slowed down the POD activity of fresh walnuts in the early stage and had the best inhibitory effect on nut kernels.Nut kernels remained the high total phenol content in the early frozen storage and the green fruit kernels maintained the high total phenolic content in the middle and late storage period.The peak of H₂O₂ was delayed at-20? in nut kernels,and maintained the lower H₂O₂ content and O₂^-·production rate in the early frozen storage.The rate of the high FRAP value in the middle and late stages of the nut seed was maintained.At the same time,the frozen treatment enhanced the cell membrane permeability of the fresh walnuts,and the relative conductivity of green fruit changed relatively smoothly.?4?Frozen storage slowed down the fat degradation of fresh walnut kernels.The effect of-40? on slowing down fat degradation was more obvious than-20?.Frozen storage could slowed down the rancidity of fresh walnut kernels.The frozen storage accelerated the fat oxidation of fresh walnut kernels in the early stage,and the oxidation of frozen nut kernels at-20? was the least.?5?In summary,it was determined that-20? is a suitable frozen temperature for fresh walnuts,and nuts are the most suitable storage form among green fruits,nuts and kernels.