Chilling injury tolerance induced by quarantine hot water treatment in mango fruit is associated with an increase in the synthesis of gallotannins in the pulp

The quarantine hot water treatment (HWT) reduces the chilling injury (CI) symptoms in mango fruit. In 'Keitt' mango this effect is associated with up-regulation of the secondary metabolism in the peel, specifically higher accumulation of gallic acid derivatives, but the metabolic changes of the pulp are unknown. This study analyzed metabolic and expression changes in the pulp of 'Keitt' mango to further elucidate the mechanisms associated with the HWT-induced CI tolerance. Mangoes with HWT (46.1 degrees C, 90 min) and control were stored under CI conditions (20 days at 5 degrees C) and then ripened (7 days at 21 degrees C). Methanol extracts were analyzed for total phenolics (TP), antioxidant capacity (ABTS, DPPH, FRAP) and phenolic profiles by UPLC-DAD-MS; the expression of genes encoding phenylalanine ammonium lyase (PAL), chalcone synthase (CHS) and glucosyltransferase (UGT) was analyzed by RT-qPCR. HWT alleviated CI symptoms and protected the membrane integrity as evidenced by lower CI index, electrolyte leakage, and malondialdehyde content values. The metabolites identified (20) were classified as gallotannins, gallic acid derivatives, benzoic acid derivatives, phaseic acid derivatives, and flavonoids. After cold storage and ripening, HWT fruit had higher levels of gallotannins, the most abundant compounds, and other metabolites such as p-hydroxybenzoic acid hexoside and dihydrophaseic acid hexoside. HWT fruit also had higher expression of the UGT gene and higher values of TP and antioxidant capacity (ABTS, DPPH, and FRAP). Thus, the HWT-induced CI tolerance in mango fruit is associated with an enhanced antioxidant capacity in the pulp due to the increased synthesis of gallotannins.

Automated summary

Activation of specific secondary metabolism pathways in the peel can alleviate chilling injury in mango fruit; however, the metabolic changes in the pulp are still unclear. This study investigated the metabolic and expression changes in the pulp of 'Keitt' mango to further understand the mechanisms of heat water treatment-induced chilling injury tolerance. The results showed that heat water treatment reduced chilling injury symptoms, protected membrane integrity, and increased the levels of certain secondary metabolites and antioxidant capacity in the pulp.