ACTIVITY OF CELL WALL SOFTENING ENZYMES AND ITS RELATION TO FRUIT FIRMNESS DURING CHEMICALLY REGULATED RIPENING TOMATO (SOLANUM LYCOPERSICUM L.)

Studies were conducted to find out the influence of six postharvest chemical treatments (CaCl₂ at 1 and 2%; GA3 at 75 and 150 ppm; spermine at 100 and 200 ppm; ethanol 2 and 4 ml kg^-1 fruit; menadione at 100 and 200 ppm; ethrel at 250 and 500 ppm) on the enzyme activity, fruit firmness and shelf life of tomato cultivar ‘PKM-1’. Fruits at breaker stage after chemical treatments were studied for their postharvest ripening behaviour at ambient temperatures in open ventilated plastic trays. The activity of cell wall softening enzymes viz., polygalacturonase (PG) and pectin methyl esterase (PME) increased gradually during storage reaching its peak by the ninth day after storage followed by a decline towards the end of storage while the fruit firmness gradually decreased during storage. Though the pattern of changes observed was similar for all the treatments including untreated control, the enzyme activity was relatively low and the rate of decrease in fruit firmness was much lower in treated fruits than those untreated. Among the chemical treatments, spermine and ethanol were found to be more effective in delaying softening by inhibiting the activity of both the enzymes during ripening and the shelf life of tomato could be extended by 10-12 days over the untreated control with the postharvest application of these two chemicals.