Role of sugar and energy metabolism in apple flesh browning during cold storage

In order to uncover the roles of soluble sugars and energy levels in the flesh browning of apple fruit during refrigeration, the differences of sugar and energy metabolism among the normal flesh tissue of normal fruit (Control) and the normal (FN) and browning (FB) tissue of browning fruit were investigated. Results revealed that the FB tissue exhibited the lowest levels of fructose, glucose, and sucrose. The activities of acid/neutral/cell wall invertase and their transcriptional levels were highest in FB tissue, while sucrose synthase and sucrose phosphate synthase have the opposite. Moreover, succinic dehydrogenase, cytochrome-c oxidase, H+-and Ca2+- ATPase activities were down-regulated in the FB tissue, resulting in the lowest levels of energy charge, adenosine triphosphate, and adenosine diphosphate compared with the non-browning tissues. These findings suggest that the browning of apple flesh during cold storage is associated with a decrease in soluble sugars and energy levels.