Effect of Cold and Heat Shock Treatment on the Color Development of Mature Green Tomatoes and the Roles of Their Antioxidant Enzymes

Color is the most important marker of the quality and ripeness of tomato fruits. To study the effect of cold shock treatment (CST; 0 °C, 3 h) and heat shock treatment (HST; 50 °C, 2 min) on the color development of mature green tomatoes and the roles of antioxidant enzymes, we measured color, the levels of malondialdehyde (MDA), ascorbic acid, and antioxidant enzymes at 20 and 10 °C storage conditions. HST retarded the ripening of mature green tomatoes, delayed color development, reduced MDA content, and increased superoxide dismutase (SOD) and peroxidase (POD) activities in tomatoes stored at 20 or 10 °C, as well as increased catalase (CAT) activity in tomatoes stored at 10 °C. In comparison with controls, CST accelerated the development of senescence in mature green tomatoes stored at 20 or 10 °C, which reflects faster color development and higher MDA content, resulting from the low activities of SOD and POD. These results suggested that, with regard to the antioxidant enzymes SOD and POD, CST had a different effect on color development compared with that of HST in mature green tomatoes stored at 20 or 10 °C. Furthermore, these results implied that SOD and POD played significant roles in the antioxidant system in CST- and HST-treated mature green tomatoes stored at 20 or 10 °C, and CAT was the crucial antioxidant enzyme to resist cold storage in HST-treated mature green tomatoes stored at 10 °C.