Changes in activities and gene expression of enzymes associated with cell wall modification in peels of hot water treated bananas

Abstract

Fruit softening is an important event during ripening that affects quality and postharvest shelf life. Cell wall degrading enzymes are considered to be the main factor responsible for cell wall disassembly and texture changes in fruit, both pulp and peel. To elucidate the effect of hot water treatment (HWT, 50°C, 10min) on the softening of ‘Hom Thong’ banana, firmness, the activities of cell wall degrading enzymes, and the expression of related genes were investigated in the peel. The firmness of banana fruit decreased throughout the storage period; however, the decrease in firmness was delayed in hot water treated fruit as compare to control fruit during storage at 25°C. Treatment of intact fruit with hot water reduced activities of pectate lyase (PL) and β-galactosidase (β-Gal) in the peel, and also decreased the accumulation of their mRNAs (MaPL1 and MaGAL, respectively). Polygalacturonase (PG) enzyme activity was inhibited by heat treatment, and the increase in MaPG1 expression was delayed. HWT had little effect on pectin methylesterase (PME) or β-1,3 glucanase (Glu). After treatment, reduced PME activity was measured in the peels, but activity returned to levels similar to that of control fruit. PME activity varied during storage and did not correlate well with MaPME1 expression. There was no significant difference in Glu enzyme activity or MaGLU expression between treated and control fruit. Postharvest HWT was effective in delaying softening of ‘Hom Thong’ banana and reduced activities and gene expression of some enzymes associated with cell wall modification in the peel.