Effect of saturated air heat treatments on weight loss reduction and epicuticular changes in six varieties of cactus pear fruit (Opuntia spp.)
Keywords:postharvest, micro-structure, epicuticular wax, transpiration.
Cactus pear (Opuntia spp.) is a not climacteric fruit, nonetheless it is highly perishable. Fruit is easily damaged showing lesions, rotting, and high transpiration rates. These events occur in the peel, and the impact can depend on, among other factors, the morpho–anatomical characteristics of its structure. In this study weight loss, respiration rate, cuticle thickness, and epicuticular micro–structure were evaluated in six varieties of cactus pear in response to different vapor heat treatments (35, 38 and 42 ± 1ºC for 12 and 24 h) after storage for 15 d at 20°C and 75% RH and 30 d at 10ºC and 95% RH. Vapor heat treatment reduced fruit weight loss, in general, an effect related to treatment. For non refrigerated fruits, the treatments that caused the highest weight loss reduction, compared to the control were 38°C for 12 h in Alfajayucan variety (61% reduction), and 35°C or 38°C for 12 or 24 h in Sangre de Toro variety (up to 51% reduction). For cold stored fruits, the treatments in which weight loss was lowest were 38ºC for 12 or 24 h with the variety Alfajayucan (1.4 or 1.53% weight loss, respectively); 38ºC for 12 h with the varieties Cristalina and Rojo Pelón (0.92 and 2.27% weight loss, respectively). All these treatments caused rearrangement of the epicuticular wax layers, minimizing or eliminating cracking. This rearrangement can partially explain the positive effect in weight loss reduction. However, vapor heat treatment in general, caused little effect on respiration rates and cuticle thickness of fruit.