Study On The Mechanism Of Reducing Chilling Injury With Cold Shock Treatment In Banana Fruit

Banana belongs to Musa(Musaceae)banana species,which was one of the largest trade,consumption fruits in the world and largest planting fruits in the south of China.It can be harvested all the year round.Their rich nutrition and aromatic taste were deeply loved by people.At present,cryopreservation was the most widely used and effective method of storage in our country.However,the banana was very sensitive in low temperature and vulnerable to chilling injury,which was caused brown and spots after ripening;At normal temperature,banana fruit was high respiration metabolism activity,easy to accelerate mature,which leads to reduce the commodity value and restrict the development of the banana fruits industry.Cold shock treatment was physical preservation method on postharvest fruits and vegetables by frost damage short-term low temperature processing to improve the storage quality.But there was few studied of cold shock treatment to reduce banana fruits chilling injury.The low temperature is far lower than the critical temperature and used to select treatment time and temperature of banana fruit.The indexes of cold shock treatment on banana fruits ripening and cold resistance physiological,active oxygen metabolism,lipoxygenase and membrane lipid fatty acids,polyamines and ethylene were studied.The purposes were to explore the mechanism of banana fruits chilling injury and provide theoretical basis for reducing chilling injury of banana fruits.The results showed as follow:1.Effects of Cold Shock Treatment on Ripening and Cold Resistance of Banana FruitsBanana fruits were treated by 0℃ cold shock 2h,3h,4h,5h and 3℃ cold shock treatment 4h,6h,8h,10h,then stored at(8±0.5)℃ of 30d and artificial ripening at(20±0.5)℃ of the cold storage,chilling injury symptoms and ripening condition were observed;simple(8±0.5)℃ served as control group.The cold resistance was determined at(8±0.5)℃ by 3℃ cold shock treatment 6h.The results showed that:compared with the control group,3℃ cold shock 6h significantly reduced the chilling injury index,improved the ripening quality and prolonged the shelf life.In addition,3℃ cold shock treatment 6h delayed banana peel cell membrane permeability,reduced malonaldehyde(MDA)content,improved soluble protein and free proline content of banana.In summary,3 ℃ cold shock 6h treatment not only effectively maintain the ripening quality and prolonged the shelf life of banana fruits,but also significantly improved the cold resistance of banana fruit.2.Effects of Cold Shock Treatment on Active Oxygen and Antioxidase Activity of Banana FruitsIn this study,the effects of cold shock treatment on banana fruits active oxygen and antioxidase activity were studied during crypreservation in order to reduce chilling injury and explore the effect mechanism of cold shock treatment.Banana fruits with 3℃ cold shock treatment 6h and without a cold shock treatment were stored at(8±0.5)℃ related physiological indicators were regularly sampled and measured.The results showed as follows:3℃ cold shock treatment 6h reduced the contents of O2-and H2O2,delay SOD activity increased,enhanced the activities of SOD,CAT and POD,delayed enzyme activity,improved the ability to organize free radical scavenging defense system,thereby reducing the chilling injury of banana fruits.In summary,3℃ cold shock treatment 6h increased activity of antioxidant enzymes to improve crypreservation of banana fruits during cold resistance.3.Effects of Cold Shock Treatment on Lipoxygenase and Lipid Fatty Acids of Banana FruitsBanana fruits with 3℃ cold shock treatment 6h and without a cold shock treatment were stored at(8±0.5)℃,and analysised the influence of cold shock treatment on banana fruits lipoxygenase activity and membrane fatty acid composition and content.The result showed as follows:(1)Banana pulp contained eight kinds of fatty acids,respectively tridecane acid(C 18:0),heptadecanoic acid(C17:0),shun-10-heptadecenoic acid(C17:1),anti-linoleic acid(C18:2),linoleic acid(C18:2),arachidic acid(C20:0),γ-linolenic acid(C 18:3)and α-linen acid(C 18:3).Saturated fatty acids mainly was tridecanoic acid,unsaturated fatty acids mainly was linolenic acid.(2)Compared with the control group,cold shock treatment significantly inhibited the lipoxygenase activity,tridecane acid,heptadecanoic acid,arachidic acid content were increased.In addition,it effectively delayed the shun-10-heptadecenoic acid,anti-linoleic acid,linoleic acid,γ-linolenic acid,a-linolenic acid content were decreased,and maintained higher index of unsaturated fatty acid(IUFA)and unsaturated degree of fatty acids.Therefore,3℃ cold shock treatment 6h improved cold resistance of banana fruits during cryopreservation.4.Effects of Cold Shock Treatment on Polyamines and Ethylene of Banana FruitsTo study the effects of pre-storage cold shock treatment(CST)at 3℃ on polyamines(Put,Spd,Spm)and ethylene of cold-stored banana fruits in relation to chilling injury were investigated.Banana fruits were treated with cold air at 3℃ with 6h,and then stored at(8±0.5)℃ the contents of polyamines and ethylene were determined;simple(8±0.5)℃ served as control group.It was indicated that there was a relatively apparent positive relationship between Put and ethylene;Spd and Spm slightly declined with ethylene’s increasing.Compared with the control group,cold-stored banana fruits pre-treated with CST at 3℃ for 6h not only decreased the contents of Put and ethylene but also delayed the value of Put and ethylene,and inhibiting decrease contents of Spd and Spm.Therefore,the chilling resistance of banana fruits was enhanced.