Effect of heat treatment on changes in softening, pectic substances and activities of polygalacturonase, pectinesterase and β-galactosidase of ripening mango

The relationship between softening, pectic substances, polygalacturonase (EC 3.2.1.15), pectinesterase (EC 3.1.1.11) and beta-galactosidase (EC 3.2.1.23) during ripening of heated and non-heated mango (Mangifera indica L.) fruits cv. Nam Dokmai was investigated. Fruit softening was accompanied by a progressive increase in water-soluble and ammonium oxalate-soluble pectin and a progressive decrease in alkali-soluble pectin. Polygalacturonase and beta-galactosidase activities increased while pectinesterase activity decreased continuously during softening. Heating fruits for 3 days at 38 degrees C resulted in an increase in softening, ammonium oxalate-soluble pectin and activity of beta-galactosidase, and a decrease in alkali-soluble pectin and activities of polygalacturonase and pectinesterase, while heating had no pronounced effect on water-soluble pectin. Softening of ripening mango fruits was more closely related to changes in beta-galactosidase activity than to polygalacturonase and pectinesterase activities. The possibility that softening of Nam Dokmai fruits is affected by mechanisms other than involvement of only polyglacturonase and solubilization of the polygalacturonide backbone of the pectin is discussed.