| Cherry tomatoes are brightly colored,aromatic,juicy and rich in carotenoids and vitamins,and have gained worldwide popularity.However,fresh cherry tomatoes lose the nutrient supply from the mother plant after detachment,and the stored nutrients are continuously depleted,water is continuously dissipated,defenses are reduced,and commercial value is severely reduced.Low voltage electrostatic field(LVEF)preservation technology affects certain physiological metabolic activities of fruits and vegetables by creating an electric field environment,which is reflected in the increase of nutritional value and shelf life.In this study,LVEF preservation technology was applied to cherry tomatoes,and the effect of LVEF application on the storage quality of cherry tomatoes after harvesting was firstly investigated,and the mechanism of LVEF preservation was explored from the perspective of antioxidant metabolism.Finally,the effects of LVEF preservation technology on the quality of cherry tomatoes at different temperatures were investigated,and a shelf-life prediction model was established for the application of LVEF technology.The results of the study are summarized as follows:(1)Cherry tomatoes were continuously treated with LVEF at 23℃ and 75% RH storage conditions,and quality indexes such as weight loss,hardness,soluble solids,and titratable acid were measured periodically without LVEF as a control to compare the freshness preservation effects.The results showed that LVEF could effectively maintain the freshness of cherry tomatoes,inhibit their weight loss,slow down the decline of color,soluble solids content,titratable acid content,hardness and lycopene.Meanwhile,LVEF treatment effectively promoted the accumulation of total phenols and total flavonoids in cherry tomatoes during the pre-storage period,which improved the functional and nutritional values of cherry tomatoes.(2)The effects of LVEF on the antioxidant metabolic system of cherry tomatoes during storage were investigated by continuously applying LVEF to cherry tomatoes under storage conditions of 23℃ and 75% RH,with no LVEF applied as a control,and by periodically measuring the content of non-enzymatic antioxidants related to antioxidant metabolism and the activity of antioxidant enzymes.The results showed that LVEF caused an increase in the hydrogen peroxide content of cherry tomato fruits through external electric field stimulation at the early stage of storage,which in turn caused an enhanced defense response in cherry tomatoes,resulting in a decrease in the hydrogen peroxide content and lipid peroxidation in LVEF-treated cherry tomato fruits after 38 h.In addition,LVEF enhanced the ability of cherry tomato fruit to scavenge reactive oxygen species and improved the level of antioxidant metabolism by increasing the levels of a range of non-enzymatic antioxidants such as ascorbic acid and reduced glutathione and the activity of antioxidant-related enzymes such as superoxide dismutase,ascorbate peroxidase and glutathione reductase,which in turn delayed ripening and aging.(3)The effects of two commonly used commercial prepackaging methods,PP freshness bags and PET freshness boxes,on physicochemical parameters of cherry tomatoes during storage were investigated under storage conditions of 23℃,75% RH and continuous application of LVEF.The results showed that the combination of PET boxes with LVEF treatment significantly suppressed the loss of quality,hardness,soluble solids and titratable acids of cherry tomatoes during storage,while PP bags did not significantly suppress the loss of quality,hardness,soluble solids and titratable acids of cherry tomatoes in the LVEF storage environment.The use of PET boxes was more suitable as a pre-packaging method based on LVEF preservation technology,and its preservation effect was better than that of unpackaged cherry tomatoes in terms of suppressing quality and firmness losses.(4)The effects of four temperature conditions,4℃,15℃,23℃ and 35℃,on the physicochemical indexes of cherry tomatoes packed without packaging and in PET freshness boxes during storage were investigated under 75% RH and continuously applied LVEF storage conditions.The results showed that the physicochemical indexes of cherry tomatoes based on LVEF preservation technology were strongly influenced by temperature,whether packaged or not,and changed rapidly at high temperature of 35℃,while at low temperature of 4℃,the physicochemical indexes changed extremely slowly.Pearson correlation analysis was used to determine the weight loss rate as a representative index for both the LVEF group and the LVEF combined with PET packaging group,and a shelf life prediction model based on the weight loss rate index under both preservation conditions was established in combination with the Arrhenius equation.The calculated and measured values of shelf life of cherry tomatoes at different storage temperatures under unpacked and preserved in PET boxes based on LVEF preservation technology were compared,and the results showed that the average relative errors of both prediction models were less than 10%.In conclusion,LVEF is a highly promising physical preservation technology and has demonstrated good preservation effects in postharvest storage of cherry tomatoes.The research in this thesis lays the theoretical foundation for LVEF and its commercial application. |
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