285 The Effect of Hot Air Treatments in Air or in Low O 2 Atmosphere on the Quality and Antioxidants of Tomato Fruit E. M. Yahia 1 *, G. Soto 2 , J. Brecht 3 , A. Gardea 2 , and M. Steta 4 1 Facultad de Quimica, Universidad Autonoma de Queretaro, Queretaro, Mexico E-mail: yahia@uaq.mx) 2 CIAD, Hermosillo, Sonora, Mexico 3 Department of Horticulture, University of Florida, Gainesville, FL, USA 4 Agros, SA de CV, Colon, Queretaro, Mexico Keywords: Postharvest, Lycopersicon esculentum, controlled atmosphere, chlorophyll, carotenoids, β-carotene, lycopene, tocopherol, enzymes Abstract Tomato fruit is an excellent source of antioxidants. However, the fruit is sensitive to chilling injury (CI). We have determined the effect of forced hot air treatments on the quality, CI, and the contents of some antioxidants. ‘Rapsody’ tomato fruit was exposed to 34ºC for 24 h in air, to 38ºC for 24 h in air, or to 38ºC for 24 h in 5% O 2 , all at low RH, and then stored in air at 4ºC or 10ºC for up to 30 d. Fruit exposed to 38ºC at 5% O 2 were injured the most, while fruit that were not heated, and those heated in air at 34ºC for 24 h were the least injured. Fruit that were maintained at 10ºC and were previously either not heated, or heated at 34ºC developed the best color when ripened, having the least chlorophyll and the highest lycopene contents. Color developed slowly at 4ºC than at 10ºC. β-carotene increased in fruit that were not heated and to a lesser extent in those that were heated in air at 34ºC or 38ºC. Fruit that were exposed to 38ºC in 5% O 2 had lower α–tocopherol content and higher peroxidase, ascorbate peroxidase, superoxide dismutase, glutathione reductase, and glutathione S-transferase activity than fruit of other treatments. We conclude that heating of tomato fruit at 34ºC for 24 h caused the least injury and fruit color developed adequately. INTRODUCTION Tomato fruit is sensitive to CI at temperatures below 7-10°C (Cheng and Shewfelt, 1988). Heat treatments have been proposed to ameliorate CI (Lurie, 1998). However, the effect of heat treatments in tomato is variety-dependent. For example treatment of mature-green ‘Trust’ tomatoes with forced air at 38°C and 50% RH for 24 h injured the fruit, increased weight loss, prevented the development of red color and reduced the production of ascorbic acid (Yahia et al., 2000). Heat treatments in controlled atmospheres have been tested for insect control (Yahia and Ortega, 2000), but have not been tested for CI amelioration. The objective of this work was to study the effect of postharvest hot air treatments in air at 34°C or 38°C or in low O 2 atmosphere at 38°C for 24 h at 50% RH on quality, important pigments, and on some of the important antioxidants in tomato fruit. MATERIALS AND METHODS Tomato fruit (Lycopersicon esculentum, ‘Rapsody’) were grown in a greenhouse and fruit were harvested in the mature-green stage. One lot of fruit was heated in air at 38°C, another lot was heated in air at 34°C, a third was heated in 5% O 2 at 38°C, all for 24 h and at 50% RH, and the fourth lot was not heated (control). Fruit of each treatment were then divided into 2 groups and stored either at 4°C or 10°C and 85% RH. Heat treatments and controlled atmospheres (Fig. 1) were conducted inside a purpose built gas-tight, temperature-controlled, and forced-air chamber (Ortega and Yahia, 2000a; Ortega and Yahia, 2000b; Yahia and Ortega, 2000; Yahia et al., 1997). Fruit were evaluated for up to 30 days for injury, weight loss, color, chlorophyll content, carotenoids, α-tocopherol, ascorbate peroxidase activity, and activity of super- Proc. Int. Conf. Quality in Chains Eds. Tijskens & Vollebregt Acta Hort. 604, ISHS 2003