Antioxidant enzyme activities, protein changes and transcript accumulation of cell wall hydrolases associated with hot water immersion treatment of 'Nam Dok Mai' and 'Ok Rong' mangoes

Abstract

‘Nam Dok Mai’ and ‘Ok Rong’ mango were harvested at the green-mature stage. The fruits were divided into two groups and treated with hot water at 50±1ºC for 10 min and 30±1ºC for 10 min as control, and then stored at 8ºC and 12ºC. Mango fruits were randomly sampled for physiological change analysis every 5 days for 15 days and then transferred to ripen at ambient temperature and sampled everyday for 5 days. Weight loss, pulp firmness, peel color, total soluble solids (TSS) and titratable acidity (TA) were analyzed. The results showed that weight loss and TSS of mangoes increased significantly, while firmness and TA decreased significantly in all treatments during storage. The peel of fruit stored at 8°C remained green longer than that of fruit stored at 12°C until the end of 20 days. Heat treatment affected weight loss, TA and TSS in both cultivars of mangoes. Ethylene production of HWT fruit both stored at 8°C and 12°C were reduced during the storage period. Mango peel and pulp were collected for lipoxygenase (LOX) protein and antioxidant enzyme assays. The activities of catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) in HWT fruit were much higher than those in control fruit on day 15. Mango peel exhibited greater physiologically response to hot water treatment than pulp of mango. Protein pattern of mango peel and pulp were detected by 10% SDS-PAGE showing 29 visible bands with the range of molecular weight from 12 to 347 kDa. Hot water treatment enhanced the accumulation of LOX protein in mango fruit. Transcript accumulations in mango pulp were also investigated. The increase in transcript levels of superoxide dismutase (SOD) was observed in HWT fruit during low temperature storage. Hot water treatment delayed transcript accumulation of pectate lyase (PL) and β-galactosidase during ripening at ambient temperature. Taken together, these results provided supporting evidence that hot water treatment affected ‘Nam Dok Mai’ and ‘Ok Rong’ mango fruit ripening.