Superficial scald development in 'Granny Smith' and 'Nicoter' apples: The role of key volatile compounds when fruit are stored under dynamic controlled atmosphere

A positive correlation of alpha-farnesene and its oxidation metabolites with superficial scald is commonly reported in apples stored in air or controlled atmosphere (CA) systems, where O2 levels are above the lower oxygen limit (LOL) tolerated by the fruit. Nevertheless, the LOL can be monitored by the dynamic controlled atmosphere (DCA) techniques and to provide different physiological responses. Therefore, this study aimed to evaluate key volatile metabolites from 'Granny Smith' and 'Nicoter' ('Kanzi (R)') apples stored under dynamic controlled atmosphere (DCA) monitored by respiratory quotient (RQ), i. e. at extremely low oxygen partial pressures (ELO) and correlate their emissions with the incidence of superficial scald (SS). The volatile compounds (VCs) were isolated by solid phase microextraction (HS-SPME) and analyzed by gas chromatography. For the first time, higher concentrations of alpha-farnesene and its oxidation metabolites (6-methyl-5-hepten-2-one, and 6-methyl-5hepten-2-ol) were negatively correlated with SS in DCA-RQ. This is likely due to the higher levels of ethanol in fruit stored under this condition having an inhibitory effect on SS incidence even when alpha-farnesene, 6-methyl5-hepten-2-one, and 6-methyl-5-hepten-2-ol accumulate. Additionally, SS is more correlated to internal ethylene concentration (IEC) than alpha-farnesene accumulation and their metabolites, even when fruit were stored under ELO, where ethylene action is reduced.