Pectin solubilization and depolymerization during papaya fruit softening

The main changes in cell wall composition as well as the degradation of water soluble pectins that correlate with postharvest softening of papaya fruit (Carica papaya L. cv. 'Maradol') were studied. Fruits in the maturity stage of 1/2 (50-75 % of yellow-orange peel color) were submitted to treatments for delaying or advancing ripening with 300 nL L-1 of 1-methyleyclopropene (1-MCP) or 2.5 g L-1 of 2-chloroethyl phosphonic acid (ethephon), respectively. Treated fruits were stored under simulated marketing conditions (20 +/- 2 degrees C and 85 % RH) during 6 d. Firmness, changes in cell wall composition and solubility and depolymerization of water soluble pectins were monitored. Application of 1-MCP inhibited totally softening and maintained fruit firmness. After 3 d in storage, control fruits presented a loss of 69 % on firmness while ethephon-treated fruits had a loss of 84 % in firmness during the same period. Fruit softening of the control- and ethephon-treated fruits were accompanied of uronic acids and total sugars solubilization from the CDTA, Na2CO3, KOH 4% and KOH 24 % fractions. An extensive depolymerization in the water soluble pectins and an accumulation of pectin-derived oligomers were only detected in control and ethephon-treated fruits, which suggests a relationship with fruit softening and a possible link to polygalacturonase action.