Efeitos do revestimento comestível à base de galactomanana e cera de carnaúba na qualidade e metabolismo antioxidante de goiabas

Abstract

The marketing of fresh guavas over long distances presents difficulties because guavas have a short post-harvest life at room temperature (about nine days). Due to this problem, storage techniques have been studied to delay ripening and enhance the postharvest quality. 'Paluma' guavas harvested at physiological maturity were divided into four groups, two control groups one kept at room temperature (25 °C) and another refrigerated (11 °C); the third and fourth coated with galactomannan-carnauba wax edible coating and stored at room and refrigeration, respectively. The fruits were stored for 15 days and evaluated every three days regarding their respiration, the antioxidant metabolism [production of hydrogen peroxide (H2O2), activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX)], variables associated with firmness [lipid peroxidation (LP), activities of polygalacturonase (PG) and pectin methylesterase (PME)], color [chlorophyll and carotenoid contents] and polyphenol oxidase activity (PPO). Coating and refrigeration extended the postharvest life of fruits to 15 days, while the 9th day of storage, control fruit were no longer apt for consumption due to undesirable firmness and color. Regarding fruit respiration, control showed a peak at nine days (114.8 mg CO2.Kg-1 FW.h-1). At the coating delayed the peak to 12th day (168.6 mg CO2.Kg -1 FW.h-1) and when associated to refrigeration, lower levels of CO2 (59.3 mg CO2.Kg-1 FW.h-1) were maintained throughout storage. The combination of coating and refrigeration maintained fruit firmness (55 N) until 15 days of storage, while coated samples at room temperature (25 °C) showed the same firmness for only six days. The combination of the two treatments also reduced H2O2 production, maintained chlorophyll content and color, delayed the activity of cell wall hydrolytic enzymes and increased enzymatic antioxidant activity (p <0.05) compared to the other treatments. Guavas coated and stored at room temperature (25 °C) had a carotenoid content much lower (35.99 mg.Kg-1 FW) than control on the 15th day. The control fruit stored under refrigeration showed a reduction in lipid peroxidation degree and in PPO activity. The results suggest that the galactomannan-carnauba wax edible coating associated with refrigeration is the best postharvest treatment for slowing down ripening and delaying senescence of 'Paluma' guava.