Studies On Effects And Mechanisms Of Cold Shock Combined With Glycine Betaine Treatment On Chilling Injury Of Zucchini Fruit

Zucchini is rich in dietary fiber and vitamins,and it is popular with consumers due to its rich nutrition.However,zucchini is a kind of cold-sensitive vegetable,which is prone to chilling injury during low-temperature storage and transportation,affecting its edible quality and economic value.Therefore,how to reduce the occurrence of cold damage in zucchini,prolong the shelf life is an urgent problem to be solved.Cold shock treatment(CST),as a physical treatment method,is widely used in the field of freshness because it is non-toxic,non-polluting,non-residual,and has a significant fresh-keeping effect.Glycine betaine(GB)maintains the structure of cell membranes by regulating the osmotic pressure of plant cells.GB accumulation is related to the cold resistance of plants.Studies have found that 10 mmol/L GB treatment can reduce the cold injury of zucchini,but the effects of CST and GB combined with CST treatment on the cold injury of zucchini have not been reported.Therefore,this study investigated the effects of GB,CST and GB combined with CST on the chilling injury of zucchini fruits,and further explored the possible mechanisms,which provided the basis for the application of the GB combined with CST treatment in the cold storage of zucchini fruits.The results were as follow:1.The effect of different CST treatment time on cold injury in zucchini was studied,we found that 0,15,30,40,and 60 min CST treatments could alleviate the symptoms of chilling injury in zucchini.And the chilling injury index of CST 30 min was the lowest,so it was chosen as the optimal treatment time.2.The effects of CST,GBand GB combined with CSTtreatments on chilling injury index,relative electric conductivity,malondialdehyde(MDA)content,chlorophyll content in zucchini stored at low temperature were investigated.The results showed that three different treatments could inhibit the increase of chilling injury index,relative conductivity and MDA content,decrease chlorophyll content,a*and b*values,among which GB combined with CST treatment was the best.3.The effects of GB,CST and GB combined with CST treatments on the active oxygen metabolism and energy metabolism of zucchini fruits during storage at 4℃ for 12 days were studied.We found that three different treatments significantly increased the activity of antioxidant enzymes such as superoxide dismutase(SOD),catalase(CAT),ascorbate peroxidase(APX)and peroxidase(POD)in zucchini,maintained high DPPH and hydroxyl free radical scavenging rate,inhibited the accumulation of hydeogen peroxide(H2O2)and superoxide radical(O2·-).Moreover,the treatments could increase the enzyme activities of Ca2+-ATPase,H+-ATPase,succinate dehydrogenase(SDH)and cytochrome oxidase(CCO),maintain higher content of ATP and ADP and lower content of AMP,keep higher level of energy charge in zucchini during storage,among which GB combined with CST treatment was the best.These results showed that GB combined with CST treatment could effectively reduce the symptoms of cold injury in zucchini fruits by regulating the active oxygen and energy metabolism,maintaining energy supply,inhibiting membrane lipid peroxidation,and protecting the integrity of cell membranes.4.The effects of GB,CST and GB combined with CST treatments on the proline metabolism and polyamine metabolism of zucchini fruits during storage at 4℃ for 12 days were studied.We found that three different treatments increased the activity of Δ1-pyrroline-5-carboxylate synthetase(P5CS)and ornithine δ-aminotransferase(OAT)in zucchini fruits,reduced the activity of proline dehydrogenase(PDH),and promoted the accumulation of proline in zucchini fruits.Moreover,three different treatments maintained lower arginine decarboxylase(ADC),ornithine decarboxylase(ODC)and polyamine oxidase(PAO)activities in the fruit,increased diamine oxidase(DAO)activity,inhibited putrescine(Put)accumulation,promoted the synthesis of spermidine(Spd)and spermine(Spm),and maintained high Spd and Spm content in the fruit,of which the GB combined with CST was the best.These results showed that GB combined with CST treatment regulated the activity of enzymes related to proline and polyamine metabolism in zucchini fruit,accumulated a large amount of proline,Spd and Spm,maintained cell permeability at low temperature,and inhibited membrane lipid phase change,effectively alleviated the cold injury symptoms of zucchini fruits under low temperature storage.