Post-harvest changes in cell walls of mango fruits

Abstract

Comparative work on the structure of the cell walls of red kidney bean hypocotyls and mesocarp from unripe and ripe mango fruits showed significant differences. Cell-wall fractions from each were obtained using solvent extraction (water, alkali and acid) and enzymic (endopolygalacturonase) degradation procedures. The monosaccharide composition of each fraction was determined after TFA-hydrolysis by TLC-analysis. Greatest variation in monosaccharide compositions was observed in the water-soluble fractions which accounted for 18%, 48% and 11% of the cell walls of the bean, unripe and ripe mango, respectively. Water-soluble carbohydrates present in the mango pulp were examined by TLC, gel-filtration and ion-exchange methods. Only sucrose, fructose, glucose and high-MW polysaccharides were detected. The ripe mango contained 8 times more soluble polysaccharide than the unripe. In the ripe fruit the approximate MW of the polysaccharide fraction, which was rich in uronic acid was 40,000. In the unripe fruitpolysaccharides with MW's ranging from 40,000 to > 300,000 were detected. These polymers contained much smaller proportions of uronic acid than those from the ripe mesocarp. A crude 3 M LiCl enzyme extract from the cell walls of the ripe mango was able to solubilize 14% of prepared cell walls from the unripe fruit. The mechanism of this process was investigated. Endo-enzymes involved could not be identified. The involvement of b-galactosidase in cell-wall degradation was examined. Using p-nitrophenyl-b-D-galactopyranoside as substrate, 3 wall-bound forms of the enzyme were found in the ripe fruit and 2 in the unripe. Four soluble forms which were different from the wall-bound forms were observed in the ripe fruit. Three of these were present in the unripe fruit. The action of the enzyme forms on mango pectin and cell walls was examined. There was no evidence that any were directly implicated in cell-wall degradation. Wall-bound exopolygalacturonase was detected for the first time in the mango fruit.