Studies On The Regulation Mechanisms Of Calcium On Chilling Injury Of Postharvest Loquat Fruit

Loquat fruit is extremely susceptible to mechanical damage,microbial invasion,would easily rot deteriorate after harvest due to its thin peel and juicy characteristic,which is not conducive to long-term storage and transportation.Low temperature storage is one of the most common methods of loquat fruit after harvest.However,after long-term refrigeration,low temperature may cause chilling injury(CI)such as rough pulp,low extractable juice and imbalance of sugar-acid ratio in loquat fruit,thus losing commodity and edible value.The effects of exogenous calcium and calcium chetalor treatment on the chilling tolerance of loquat fruit during cold storage were investigated in this paper,and the possible role and mechanism of Ca2+ on reducing chilling injury of loquat fruit were discussed,in order to provide theoretical basis for loquat fruit postharvest preservation technology.The results are as follows:1.The effects of calcium on chilling injury and quality of loquat fruit were investigated.The loquat fruit was treated with 1%CaCl2 and 10 mmol/L EGTA.It was found that,Ca2 +maintained a higher level of TSS,Vc and total phenol content,while significantly inhibited the increase of internal browning,firmness,electric conductivity,MDA content and PPO activity in loquat fruit.Thereby,Ca2+ played a positive role in maintaining the soft and juicy characteristics as well as the high nutrition of the loquat fruit during cold storage.2.The effects of calcium on active oxygen metabolism and energy metabolism in cold stored loquat fruit were investigated.The results indicated that,the active oxygen metabolism related enzymes(SOD,CAT,POD,APX)and energy metabolism related enzymes(H+-ATPase,Ca2+-ATPase,SDH,CCO)were enhanced by Ca2+.Which contributed in the increase of ATP,ADP content and energy charge level,effective reduce of O2-production and H2O2 accumulation,as well as the higher scavenging ability of DPPH free radical and hydroxyl free radical in loquat fruit.The effect of Ca2+in alleviating cold damage and improving cold tolerance was carried out by maintaining the balance of active oxygen metabolism and improving energy metabolism in loquat fruit.3.The effect of calcium on metabolisms of proline,GABA and polyamines in cold stored loquat fruit were investigated.The results showed,Ca2+significantly increased the activity of P5CS,OAT,GAD,and inhibited PDH activity in the same time,thereby promoting the accumulation of proline and GABA content.In the mean time,Ca2+maintained higher polyamines content and promoted the activity of DAO and PAO to generate GABA.The effect of Ca2+in reducing the damage of low temperature in loquat fruit was carried out by promoting the metabolisms of proline,GABA and polyamines.