Tragacanth gum coating suppresses the disassembly of cell wall polysaccharides and delays softening of harvested mango (Mangifera indica L.) fruit

Abstract

Mango is a climacteric fruit and is prone to high perishability. The rapid softening and ripening (due to degradation and disassembly of cell wall polysaccharides) are the major limitations in extending the storability of the harvested mango fruits. Various types of gum-based edible coatings have been reported for the shelf life extension of mango fruits. Tragacanth gum (TCG) also has appropriate coating properties. Its use as an edible coating has been reported on certain fruits. However, the effect of TCG coating in the regulation of harvested mango fruits ripening and softening has not been reported yet. So, the objective of this work was to investigate the effect of TCG (control, 0.5 %, 1 % and 1.5 %) coating on postharvest softening and ripening of harvested mango fruits. TCG coating affected the ripening and softening of mango in a dose-dependent manner. Results exhibited that mango fruits coated with 1.5 % TCG showed substantially lower disease incidence and weight loss. The 1.5 % TCG-coated mangoes showed substantially lower ethylene biosynthesis and respiration rate peaks as well as superoxide anion and hydrogen peroxide contents compared with the control. In the same way, 1.5 % TCG-coated mango fruits had markedly higher total chlorophyll content and lower L*, b* and a* along with substantially lower total carotenoids in peel tissues. Mango fruits coated with 1.5 % TCG exhibited markedly lower water-soluble pectin and higher chelate-soluble pectin, Na₂CO₃-soluble pectin, protopectin, cellulose and hemicellulose in flesh tissues compared with control. The activity of polygalacturonase (PG), cellulase (CX), pectin methylesterase (PME), β-galactosidase (β-Gal) and β-glucosidase (β-Glu) were significantly lower in flesh of 1.5 % TCG treated fruits along with substantially higher firmness in contrast with control. In addition, 1.5 % TCG coating treatment showed significantly higher activity of antioxidative enzymes and delayed the increase in soluble solids content (SSC) and ripening index (RI) along with considerably higher titratable acidity (TA) compared with the untreated control. So, pre-storage TCG based edible coating (1.5 %) could be applied to delay ripening and softening in mango fruit industry under postharvest ambient conditions.

Keywords: Cell walls disassembly; Cellulose; Fruit softening; Hemicellulose; Mango; Protopectin.