Effects of postharvest hot water treatment on physiological and biochemical properties of eksotika II papaya during ripening / Arina Mhd Arshad

Arina, Mhd Arshad (2011) Effects of postharvest hot water treatment on physiological and biochemical properties of eksotika II papaya during ripening / Arina Mhd Arshad. Masters thesis, University of Malaya.

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Abstract

The effects of postharvest hot water treatment (HWT) on the quality of ‘Eksotika II’ papaya fruit harvested at different harvesting maturities were investigated. HWT is a method for fruit fly disinfestation which is a quarantine requirement for the fresh papaya exportation industries in Malaysia. Fruit at maturity stages Index 1 (H1), Index 2 (H2) and Index 3 (H3) were harvested. From each maturity stage, one group of the papaya fruit batch was treated with hot water at 47±1˚C fruit core temperature held for 10 minutes and another group was untreated. Fruit were left to ripen at ambient temperature (25˚C) and were taken into experiment at the subsequent ripening stages at Index 2, Index 3, Index 4 and Index 5. Physiological changes including skin colour (L*a*/b*), weight loss, fruit firmness, total soluble solids (TSS), pH and chlorophyll fluorescence were determined at each different ripening stages. Biochemical changes including total sugar, total reducing sugar, total non-reducing sugar and cell wall degrading enzymes activities such as polygalacturonase (PG), pectin methylesterase (PME), pectate lyase (PL) and cellulase were also investigated. HWT did not give any significantly adverse effect to the physiology parameters evaluated, such as L*a*/b* value, weight loss, TSS and pH. However, the treated Index 3 and Index 4 of H1 fruit was slightly firmer than the untreated fruit. The chlorophyll fluorescence parameters have shown that within one hour after treatment, the treated fruit experienced heat stress which was reflected in the lower chlorophyll fluorescence parameters values, Fv/Fm. The heat stress was found to be more severe by 14 – 25 % in the H3 fruit rather than in the H2 and H1 fruit. However, the Fv/Fm value in the H3 fruit recovered by 25% during the subsequent stages of ripening. Furthermore, the total sugar and the total reducing sugar content were not adversely affected by the HWT. The pattern of cell wall degrading enzymes activity showed that PME activity decreased during ripening, whilst PG, PL and cellulase activity increased progressively during ripening. It was also found that the application of the HWT affected the cell wall degrading enzymes activity whereby it was found to be lower in the heat treated fruit. Nevertheless, pulp firmness was not severely affected since some of the enzyme activities managed to recover during the ripening period. For maximum fruit quality, particularly for export markets, it is recommended that Index 2 fruit are selected for HWT rather than H1 fruit since the H1 fruit will ripen poorly. The Index 3 Eksotika II papaya is only suitable for the local market because of its short shelf life. In summary, these observations indicated that the overall Eksotika II papaya fruit quality is still maintained following HWT when the fruit is allowed to ripen at ambient temperature. This suggests that postharvest HWT at 47 °C (fruit core temperature, held for 10 minutes) can maintain the postharvest quality of Eksotika II papaya fruit.

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