OXIDATIVE STRESS AND CHANGES IN THE LEVELS OF ANTIOXIDANT ENZYMES OF TWO VARIETIES OF Carica papaya L. DURING RIPENING

Abstract

Oxidative stress and changes in the levels of antioxidant enzymes were determined in two varieties of Carica papaya fruits (?Agric pawpaw‘: oblong shaped variety and ?Local pawpaw‘: pear shaped variety) during ripening. An increase in lipid peroxidation product, malondialdehyde (MDA); which is an index of oxidative stress, was observed in both varieties. The activity of the antioxidant enzyme, superoxide dismutase (SOD) also decreased in both varieties of Carica papaya fruits during ripening and its reduction was observed to be the major contributor to oxidative stress in Carica papaya fruits. Changes in catalase (CAT) and ascorbate peroxidase (APX) activities during ripening in Carica papaya fruits in this study were found to be dependent on the type of variety. Increase in catalase activity was observed throughout the ripening period in ?Local pawpaw‘ (pear shaped variety) (from 0.000212 ± 0.000001 to 0.000917 ± 000025 ?mole/min/g fresh weight), while in ?Agric pawpaw‘ (oblong shaped variety), the catalase activity increased from the unripe to the ripe stage (from 0.000071 ± 0.000024 to 0.000155 ± 0.000026 ?mole/min/g fresh weight) and later decreased in the overripe stage (from 0.000155 ± 0.000026 to 0.000099 ± 0.000029 ?mole/min/g fresh weight). The only changes that were observed in the activity of ascorbate peroxidase in the two varieties of Carica papaya fruits were an increase in the overripe stage of ?Local pawpaw‘ (pear shaped variety) (from 0.001427± 0.000618 to 0.002497 ± 0. 000619 ?mole/min/g fresh weight) and a decrease in the overripe stage of ?Agric pawpaw‘ (oblong shaped variety) (from 0.002497± 0.000618 to 0.0014267 ± 0.000617 ?mole/min/g fresh weight). This study revealed that reduction in superoxide dismutase (SOD) activity was a major contributor to oxidative stress in Carica papaya fruits during ripening. It also showed that the increase in oxidative stress in Carica papaya fruit during ripening contributes to its high perishability.