Antioxidative responses of ripe tomato fruit to postharvest chilling and heating treatments

The objective of this research was to determine the antioxidative responses to chilling and heating stresses in ripe tomatoes cv. 'Sanibel'. Full ripe fruit were treated with either chilling (5 °C for 5 days), hot water (52 °C for 15 min, then cooled to 25 °C with tap water), or left untreated as the control. Fruit samples were taken directly after treatment or after 4 days storage at 20 °C. Directly after treatments, heating remarkably increased the activity of lipoxygenase (LOX), and chilling increased malondialdehyde (MDA) content. LOX catalyzes the oxidation of lipids, and MDA is a compound produced from lipids under oxidative stress. The increase of LOX activity and MDA content indicates escalated reactive oxygen species (ROS) in the tissues. The heat treatment also increased ascorbate levels, and induced the activities of catalase (CAT) and peroxidase (POD) as well. After 4 days storage at 20 °C, antioxidant reductive capacity (ARC) and the activity of ascorbate peroxidase (APX) was significantly higher in the chilling treated fruit than in the control. Chilling directly increased MDA and ascorbate levels, and led to a remarkable increase in H2O2 on day 4 after treatment. The activities of CAT and POD were lower in chilled fruit than in the control on day 4 after treatment. These results indicate that oxidative stress may be induced by chilling treatment even without visual injury on the fruit surface. Heat treatment enhanced the antioxidant enzyme system to potentially protect fruit from environment stress.