Effect of gamma-irradiation on ripening papaya pectin

Abstract

Papaya (Carica papaya, L., var. Sunset) at three initial ripeness stages were irradiated with 0.25, 0.50, 0.75, 1.0, or 1.5 kGy gamma-irradiation and pectin changes during ripening determined. A significant linear relationship was found between irradiation dose and firmness immediately after irradiation. Irradiation had no effect on fruit skin or flesh color of papaya fruit irradiated at the 5 to 30% yellow stage and allowed to ripen. Papaya irradiated when 5 to 30% yellow showed no significant changes in pectin methylesterase activity when ripe. Immediately after irradiation, the pectin in 10 to 30% yellow papaya showed depolymerization and demethoxylation, though no effect on pectin methylesterase activity was detected. There was an increase in water soluble pectin (WSP), while chelator soluble (CSP) and alkali soluble pectin (ASP) decreased, with a significant decline in the methanol content of the ASP fraction. After the 25 to 30% yellow ripeness stage, fruit irradiated at 0.50 to 1.0 kGy had less pectic depolymerization, and had a firmer texture than nonirradiated when ripe. A lower level of WSP and higher levels of CSP and ASP were found in ripe fruit that had been irradiated at 0.5 to 1.0 kGy when 25 to 30% yellow skin with a significant quadratic relationship between irradiation dose and the three pectin fractions. The firmness of these irradiated fruit were retained for two days longer than the nonirradiated control.