Impact of a Different Ripening Stage, as Defined by the Index of Absorbance (IAD), on Polyphenol Metabolism and Superficial Scald Development in Apple Fruit

Ripening is the combination of a serious of physiological events occurring in the fruit at the end of its onthogenic life cycle. All these modifications led to the final fruit quality make-up. It is this that determines the most appropriate ripening stage of a fruit in order to increase storability and shelf-life, while reducing fruit spoilage. The aim of this experiment was to tailor a postharvest 1-MCP application to control apple superficial scald based on the fruit ripening at harvest. Fruit of ‘Granny Smith’ cultivar were sorted into two ripening classes based on the "Index of Absorbance" (I_AD), measured with a DA-Meter, a portable vis/NIR spectroscopy device. Superficial scald and total content of polyphenols were assessed at 2-month intervals among 4 months of cold storage (1°C). Results demonstrated that the incidence of superficial scald is directly regulated by the ripening stage at harvest, with more immature fruit being more susceptible to this physiopathy. Apple superficial scald resulted to be associated to an oxidation process leading to a specific up-regulation of the chlorogenic acid biosynthesis pathway. This compound is accumulated in the fruit skin during the scald appearance and oxidized by the action of polyphenol oxidase (PPO).  The oxidized quinonic forms are responsible for the formation of melanin and the subsequent brown discoloration). The treatment with 1-methyl-cyclopropene (1-MCP) affects both the chlorogenic acid production and the PPO activities, blocking the superficial scald progression.