Unravelling physiological and histochemical changes in two popular dessert and cooking bananas of India during fruit ripening

Abstract

The physicochemical and histochemical characteristics of two consumingly divergent commercial varieties of Musaceae (Musa cv. Kanthali and Musa cv. Kacha Kela) were investigated during their postharvest ripening. The fruit peels from both cultivars were characterised by a reduction in chlorophyll contents, loosening of cortical tissues, and shrinkage of parenchymatous cells. The pulp-to-peel ratio, total soluble sugars, reducing sugar, fruit firmness, electrolyte leakage, and respiration rate were investigated along with activities of a few enzymes involved in fruit softening, namely cellulase, xylanase, invertase and glucanase. Additionally, semi-quantitative gene expression analyses with a few ripening-related genes, including ethylene biosynthesis (MaACS and MaACO), carbohydrate metabolism viz. sucrose synthase (MaSUS), sucrose phosphate synthase (MaSPS), glucanase (MaGLU), invertase (MaINV) and pectin methyl esterase (MaPME) were also carried out along with chitinase (MaCHT) in both cultivars during postharvest ripening. A faster postharvest ripening of ‘Kanthali’ than ‘Kacha Kela’ was evidenced as an outcome of the above studies.The peel histology and surface ultrastructure were examined through light microscopy and scanning electron microscopy (SEM), respectively. In light microscopy, substantial variations were noted between the cultivars, especially on peel-tissue degradation and accumulation of metabolites. The surface ultrastructure revealed temporal variations in the peel stomatal opening along with gradual depletion of surface wax. Such temporal opening of stomata was found to coincide with our earlier recorded postharvest volatiles emission patterns of respective cultivars suggesting it to be a legible vent for aroma emission.