Effects Of Abscisic Acid Treatment On The Aroma Quality Of ‘Nanguo’ Pears After Cold Storage

‘Nanguo’ pears belongs to the Pyrus ussuriensis Maxim.,which is usually picked in early to mid September every year.‘Nanguo’ pears have a short storage period at room temperature after harvest,about 15-20 days.Because of its storage characteristics,it is usually stored at low temperature,which reduces the respiration rate of the fruit and prolongs the storage period.The study found that the fruit of ‘Nanguo’ pears that has been refrigerated for a long time is prone to chilling damage,which leads to symptoms such as lightening of the aroma and browning of the peel,which reduces its quality and affects its commercial value.In the previous research of the research group,it was found that the synthesis of the main ester aroma substances in ‘Nanguo’ pears fruit is related to the metabolism of fatty acids and the synthesis pathway of ester substances using unsaturated fatty acids as substrates.Variable temperature treatment,methyl jasmonate and betaine treatment were used to control the aroma quality of refrigerated ‘Nanguo’ pears.Abscisic acid(ABA)is a natural plant hormone.Studies have found that ABA can help plants resist some abiotic stresses,such as drought,low temperature stress,salt stress,etc.Therefore,ABA is also known as stress hormone..Some studies have also found that there is a dose effect when ABA is used to resist cold damage,and the concentration of ABA has different effects on cold damage of fruits and vegetables.In this study,‘Nanguo’ pears were treated with ABA.First,during the shelf life of ‘Nanguo’pears after 90 days of refrigeration,the appropriate ABA treatment concentration was screened by comparing the fruit maturity,ester aroma substances and nutrient content of‘Nanguo’ pears.The effect of ABA treatment on the bound aroma of refrigerated ‘Nanguo’pears was studied.Finally,the key pathways for the synthesis of main ester aroma substances in ‘Nanguo’ pears were studied,and the regulation mechanism of ABA treatment on the synthesis of refrigerated ‘Nanguo’ pears ester aroma substances was explored,to explore effective measures to improve the aroma quality of ‘Nanguo’ pears and improve its commercial value as a technical reserve.The main results are as follows:(1)In this study,ABA solutions of 0 mg/L,50 mg/L,100 mg/L and 150 mg/L were used to treat ‘Nanguo’ pears.The appropriate ABA treatment concentration was screened out by analyzing the ripeness,ester aroma and nutrient composition of the fruit during the shelf life at room temperature after 90 days of refrigeration.The study found that 100 mg/L ABA treatment had the best effect on promoting the synthesis of ester aroma substances in ‘Nanguo’pears after refrigeration,and the fruit treated with this concentration was compared with the control fruit and the subsequent related mechanism research was carried out.(2)This study further exploratively analyzed the bound aroma in ‘Nanguo’ pears.It was found that during the postharvest storage process at room temperature,with the ripening of the fruit,the bound aroma substances in the fruit were used as the reserve of free aroma gradually increasing.After low temperature refrigeration,the contents of bound esters,alcohols,aldehydes,ketones,phenolic acids and other substances in ‘Nanguo’ pears were significantly reduced.Although the types of bound aroma substances in the fruit at the best edible stage increased compared with those of the untreated refrigerated group,and the total content of bound aroma substances also increased significantly,but the total content was significantly lower than that of the fruits stored at room temperature after harvest,and the difference is very large,so it is speculated that the effect of ABA treatment on the aroma synthesis of refrigerated ‘Nanguo’ pears is mainly for the aroma of free esters,but has no significant effect on the aroma compounds in the bound state.(3)Based on the above research results,the mechanism of the effect of ABA treatment on the synthesis of ester aroma substances in ‘Nanguo’ pears fruit was further explored from the key pathway for the synthesis of main ester aroma substances in ‘Nanguo’ pears fruit.The relative content of fatty acids,lipase activity and gene expression,and the changes of gene expression related to fatty acid metabolism pathway were compared and analyzed during shelf life at room temperature.The results showed that ABA treatment promoted Pu SCD,Pu FAD2,Pu FAD6,Pu FAD3,Pu FAD7,The expression of Pufab F,Pufab G,Pufad E,Pufad J and Puato B promotes the degradation of palmitic acid and the synthesis of short-chain fatty acids,increases the relative content of linoleic acid and linolenic acid,and increases the unsaturation of fatty acid composition.The synthesis of substances provides more substrates and improves the stability of cell membranes.In addition,ABA treatment also increased the activities of key enzymes LOX,ADH and AAT in the LOX pathway using unsaturated fatty acids as substrates and promoted the expression of their corresponding genes.