The role of respiratory metabolism in chilling injury development of Chinese olive fruit during cold storage

Abstract

Chilling injury (CI) and browning occurrence are pivotal issues during the cold storage of postharvest Chinese olive fruit. This study evaluates the effects of non-chilling temperature (8 °C) and chilling temperature (2 °C) on CI development, browning occurrence, and respiratory metabolism in postharvest Chinese olives. Compared to storage at 8 °C, storage at 2 °C significantly induced CI, accompanied by higher indices of CI and browning, as well as a higher fruit respiratory rate. Storage at 2 °C increased the activities of phosphohexose isomerase (PGI), succinate dehydrogenase (SDH), ascorbic acid oxidase (AAO), and cytochrome C oxidase (CCO) by 55.1%, 11.1%, 26.4%, and 98.8%, respectively, on day 120. On the other hand, storage at 2 °C reduced the activities of NAD kinase (NADK), 6-phosphogluconate dehydrogenase (6-PGDH) + glucose-6-phosphate dehydrogenase (G-6-PDH) by 95.6% and 6.6%, respectively, on day 120. The contents of nicotinamide adenine dinucleotide (NAD) and its reduced form of NAD (NADH) increased by 10.0% and 22.8%, respectively, in fruit stored at 2 °C on day 120. Conversely, the contents of nicotinamide adenine dinucleotide phosphate (NADP) and its reduced form (NADPH) decreased by 58.3% and 64.4%, respectively, in fruit stored 2 °C on day 120. These findings indicate that CI development and browning occurrence in Chinese olives induced by storage at 2 °C were associated with a higher respiratory rate, increased activities of PGI, SDH, AAO, and CCO, higher contents of NAD(H), reduced activities of 6-PGDH + G-6-PDH, and lower contents of NADP(H).