Effect of pre-cooling and heat treatment on antioxidant enzymes profile of mango and banana

Fruits have self defense mechanisms to protect from oxidative stress by the activation of many antioxidant defense enzymes like superoxide dismutase (SOD), catalase (CAT) and peroxidase (POX). The development of oxidative stress in fruit mainly depends upon its cellular antioxidant levels, physical atmosphere of the fruit and its postharvest handling. The present investigation was carried out to study the effect of post harvest pre-cooling and heat treatments on antioxidant enzymes, CAT, POX and SOD involved in detoxification of reactive oxygen species (ROS) were measured in mango var. Alphonso and banana var. Robusta. Increased CAT and POX activities in mango and banana during heat treatment followed by cooling at 8 ºC or 13 ºC indicated increased elimination of ROS. Pre-cooling of mango at 8 ºC showed two-fold decreased CAT activity in the pulp whereas heat treatment to mango followed by cooling at 8 ºC and 13 ºC recorded 2.2 fold increased CAT activity. Pre-cooling treatment reduced POX activity whereas heat treatment followed by cooling resulted in decreased SOD activity. CAT activity after pre-cooling to 13 ºC by using pre-cooled air was similar to that of control. In banana, pre-cooling treatment (8 ºC) and heat treatment followed by cooling reduced CAT activity in peel and pulp, whereas POX activity increased. Pre-cooling and heat treatments altered normal homeostasis of these fruits, which were reflected by changes in the levels of antioxidant enzymes- CAT, POX and SOD. Visual assessment of mango and banana fruits after pre-cooling at different temperatures (5 ºC, 8 ºC and 13 ºC) did not show any chilling injury (CI) symptoms. Similarly, application of postharvest quarantine heat treatment (52-55 °C) for 5 minutes to mango showed no heat injury (HI) symptoms like skin scalding, damaged lenticels which could be due to very short duration of exposure. Extent of recommendation of pre-cooling temperature and heat treatment of these fruits after pre-cooling at 5 ºC and 8 ºC can be made based on the levels of reactive oxygen species. The present study showed that the level of expression of antioxidant enzymes got affected during pre-cooling (5 ºC and 8 ºC) and quarantine heat treatment (52-55 °C). Therefore, findings of the present study serve as basic information about cellular homeostasis in the mango and banana.