Study On The Fresh-keeping Mechanism Of Strawberry By Low Voltage Electrostatic Field Combined With Low Temperature

Strawberry fruit is sweet and nutritious,and is deeply popular with the majority of consumers.However,its delicate tissue and high moisture content make it vulnerable to mechanical damage and microbial infection in the process of picking,transportation and sale,leading to spoilage and deterioration.Therefore,appropriate postharvest preservation methods play an important role in improving its economic value.In this study,low voltage electrostatic field(LVEF),a new,non-thermal and low-cost physical fresh-keeping technology,was applied to the postharvest storage of strawberries.Firstly,the effects of LVEF treatment on the physiological quality of postharvest strawberries were explored,and the fresh-keeping mechanism of LVEF was explored from the point of view of cell wall metabolism,active oxygen metabolism and antioxidant metabolism.Then,the fresh-keeping effect of LVEF treatment on postharvest vibration-damaged strawberries was studied.Finally,the effects of LVEF treatment on the quality of fresh strawberries at different storage temperatures were explored,and a shelf life prediction model based on quality index was established.This study provides a reference for the transportation and storage of strawberries,and the specific research contents are as follow:(1)Strawberries were stored in the LVEF environment of(4 ± 1)℃ and 85%-95% relative humidity to study the effects of LVEF treatment on postharvest physiological quality and cell wall metabolism of strawberries.The changes of quality indexes such as decay rate,firmness,total soluble solids,malondialdehyde and cell membrane permeability of strawberry during storage were measured.And then the effects of LVEF treatment on the physiological quality of postharvest strawberries were analyzed,and the fresh-keeping effect of LVEF treatment on strawberries was discussed.The mechanism of LVEF on strawberry preservation was analyzed from the point of view of cell wall metabolism by measuring the changes of cell wall components(protopectin and soluble pectin)and cell wall degrading enzyme activity of strawberry during storage.The results showed that LVEF treatment reduced the degree of cell membrane lipid peroxidation and maintained the integrity of cell membrane structure,which was beneficial to maintain the quality of strawberry during storage.Meanwhile,LVEF treatment inhibited the activity of strawberry cell wall degrading enzymes(polygalacturonase,pectin methyl esterase,cellulase,β-glucosidase,xyloglucan endotransglycosylase/hydrolase and β-xylosidase),slowed down the degradation of cell wall components,and then maintained the stability of cell wall structure.(2)Strawberries were stored in the LVEF environment of(4 ± 1)℃ and 85%-95% relative humidity to study the effects of LVEF treatment on reactive oxygen species and antioxidant metabolism of strawberries.The changes of reactive oxygen species and antioxidant metabolism related indexes such as hydrogen peroxide,superoxide anion production rate,total phenols,anthocyanins,ascorbic acid,reduced glutathione,superoxide dismutase,catalase and ascorbate peroxidase were measured during storage.The mechanism of LVEF treatment on the preservation of strawberry was analyzed from the point of view of active oxygen and antioxidant metabolism.The results showed that LVEF treatment maintained the contents of antioxidant substances such as total phenols,anthocyanins,ascorbic acid and reduced glutathione,and increased the activities of antioxidant-related enzymes such as superoxide dismutase,catalase and ascorbate peroxidase,which significantly inhibited the accumulation of hydrogen peroxide and superoxide anion in strawberry fruit,thus reducing the oxidative damage of strawberry fruit and showing better physiological quality than the control group.(3)Strawberries were placed on a vibration test-bed for transportation simulation,vibrating for 1 h to simulate road transportation for 10 h.After vibration,strawberries were placed in a LVEF environment of(4 ± 1)℃ and 85% relative humidity,and the effect of LVEF treatment on the physiological quality of strawberries damaged by vibration was studied.The firmness,weight loss,respiratory intensity,total soluble solids,anthocyanins,ascorbic acid,malondialdehyde and cell membrane permeability of strawberries were measured,and the fresh-keeping effect of LVEF treatment on vibration-damaged strawberries was analyzed.The results showed that LVEF treatment could effectively maintain the firmness of damaged strawberries,reduce the weight loss and respiratory intensity of damaged strawberries,increase the retention of nutrients such as total soluble solids and ascorbic acid,and effectively maintain the integrity of cell membrane structure.LVEF treatment can effectively reduce the adverse effects of mechanical damage on strawberry fruit,and it is an effective method to maintain the quality of postharvest strawberry.(4)The strawberries were stored in the LVEF environment at 5℃,10℃,15℃,20℃ and25℃ respectively.And the decay index,firmness,weight loss,total soluble solids,malondialdehyde,anthocyanin and ascorbic acid content were measured periodically.The effect of temperature on each quality on each quality index under LVEF treatment was discussed,and the fitting equation of each monitoring index was determined.Combined with Arrhenius equation,the shelf life prediction model of fresh strawberry based on quality index was established.The results showed that the fitting degree of the prediction model of each quality index was more than 0.9,the prediction error was less than 10%.The prediction effect is good.