Study On The Relationships Between Superficial Scald With Chlorophyll Fluorescence Parameters And Volatile Compounds Of ’Granny Smith’ Apple

Although the fruit of’Granny Smith’is resistant to storage and transportation,it is prone to superficial scald in the middle and late cold storage period.The superficial scald affects the appearance quality of the peel,and reduces its storage,eventually causing huge economic losses.Therefore,the prediction and prevention of superficial scald are particularly important.The’Granny Smith’apple was used as material in this study.Apples were stored at low temperature（0℃±0.5℃）for 5 months then transferred to room temperature（20℃±0.5℃）for 21 days after superficial scald happened.The basic physiological indexes,chlorophyll fluorescence parameters（Fv/Fm）,volatile compounds and phenolic compounds in’Granny Smith’apples were regularly determined.Moreover,the correlation analyses between above parameters with incidence were also conducted to establish a prediction mechanism for large-scale incidence of superficial scald and to provide the theoretical basis for nondestructive testing.The experimental results were as follows:1)The incidence and incidence index of superficial scald in’Granny Smith’apple were both significant negatively correlated with soluble solids content,titratable acid content and firmness,while were both significant positively correlated with respiratory intensity.There is no correlation between the incidence and incidence index of superficial scald with ethylene release rate.It shows that the superficial scald of apple has significant impact on a series of basic physiological parameters.2)During the whole storage process,the content of chlorophyll a decreased from 73.48 mg·kg^-1to 36.57 mg·kg^-1after being transferred from cold storage to room temperature,with reduction of 36.91 mg·kg^-1（decrease 50%）.Meanwhile,the chlorophyll fluorescence parameters（Fv/Fm）decreased from 0.72 to 0.6 after being transferred from cold storage to room temperature for 3 days.And with the extension of shelf life,the Fv/Fm continued to decline with 0.3 as its final value.The incidence and incidence index of superficial scald in’Granny Smith’were both positively correlated with L*,b*and a*,while were negatively correlated with chlorophyll fluorescence parameters Fm and Fv/Fm,chlorophyll a,chlorophyll b,and content of carotenoids.However,there was no significant correlation between the incidence and incidence index of superficial scald with the chlorophyll fluorescence parameter Fo.The occurrence of superficial scald was accompanied by a decrease in the chlorophyll fluorescence parameter Fv/Fm.When the Fv/Fm fell from 0.7 to0.6,the superficial scald started to appear on‘Granny Smith’apple in large numbers.It shows that the chlorophyll fluorescence parameter could be used as an index to predict the incidence of superficial scald and the chlorophyll fluorescence could be detected in a non-destructive method which can be quickly and easily used in apple production.3)The changing trends ofα-farnesene,6-methyl-5-hepten-2-one and 6-methyl-5-hepten-2-ol are as follows:the content ofα-farnesene and 6-methyl-5-Hepten-2-one showed increased trend during the cold storage and reached highest values after shelf life for 3d,following by decrease of content.It is noteworthy that the incidence of superficial scald increased by 66.7%during the period of 18w to 18+3d accompanying by a sharp increase in content ofα-farnesene and 6-methyl-5-hepten-2-one.This shows that these two compounds could be used as indicator of the incidence of superficial scald.The6-methyl-5-hepten-2-ol appeared at 18 w and increased with the incidence of superficial scald which is consistent with the occurrence of superficial scald and also could be used as a predictor of the occurrence of superficial scald.4)There was a significant positive correlation between total content of flavonoids and phenolic compounds in the peel and pulp with the incidence and incidence index of superficial scald.The phenolic compounds including rutin,hyperoside,quercetin,gallic acid,and coumaric acid also had significantly positive correlations with the incidence and incidence index of superficial scald.Only the epicatechin was significantly negative correlated with the incidence and incidence index of superficial scald.There were no significant correlations between phloridzin,caffeic acid and chlorogenic acid with the incidence and incidence index of superficial scald.However,the phloridzin increased at the 14w before the onset of superficial scald,with slightly accumulation then decreased.The chlorogenic acid and caffeic acid also have same trend as the phloridzin.These three phenolic compounds could also be used as an indicator to predict the occurrence of a large numbers of superficial scald in’Granny Smith’apple.