Improving postharvest quality retention of oranges during ambient storage using hot water immersion and fruit coating: the role of internal modified atmosphere

Plants respond to sublethal stresses such as a mild hot water treatment by upregulation of their antioxidant system, which has been shown to increase the tissue resistance to subsequent exposures to stress. Fruit respiration can increase substantially when they are submerged in water at warm but sublethal temperatures. While submerged, there is also minimal gas exchange, which can create extreme internal modified atmospheres (MA) that may also be perceived by the tissues as a stress. Coatings applied to citrus fruits have also been shown to result in development of internal MA during storage that can be either beneficial or damaging to fruit quality. The purpose of this research was to explore the potential use of hot water treatments (HWT) plus fruit coatings to stimulate the fruit antioxidant system and create a beneficial internal MA to better maintain postharvest quality of orange fruit when refrigerated storage is not available. In preliminary work with ?Valencia? and ?Washington Navel? orange fruit, HWT were evaluated with temperatures from 25 to 55?C in 5?C increments and durations from 10 to 80 minutes. Those treatments resulted in internal O2 from 1 to 20% and CO2 from 1 to 30% immediately after HWT. In separate experiments, Washington Navel oranges were harvested twice from commercial groves near Fort Pierce, FL, USA and treated with thiabendazole (TBZ) for decay control on the day of harvest. The fruit were then randomized and submerged for 30 min in water maintained at 25?C or 45?C with rapid stirring. The fruit were then brush-washed with detergent and coated with polyethylene-, carnauba-, or shellac-based coatings using a centrifugal applicator on a semi-commercial citrus packingline or left uncoated. Fruit internal atmospheres (O2, CO2, and C2H4) were measured on the day of HWT and coating applications and several times during 3 weeks of storage at 25?C and 85% relative humidity. Whole fruit firmness and weight loss, peel and juice color, pulp, titratable acidity, carotenoid content, volatiles and antioxidant capacity, as well as consumer sensory quality were evaluated weekly during storage. Fruit internal atmosphere was approximately 5% O2 + 15% CO2 at the end of HWT for all treatments. Consumers in sensory panels ranked the flavor and overall quality of fruit with carnauba-based coating higher than uncoated fruit, or fruit with polyethylene or shellac coating. Shellac coating resulted in the lowest rating, which corresponded to elevated internal C2H4 (0.2 to 0.4 versus 2.7 ?L L-1) after 3 weeks, suggesting a stress response. Internal atmospheres of coated fruit were otherwise similar during storage (12-16% O2 + 4-6% CO2). ? The picture shows the level of acceptability by the customers of the different treatments.? SourcesImproving postharvest quality retention of oranges during ambient storage using hot water immersion and fruit coating: the role of internal modified atmosphereFerdous Chowdhury1, Jeffrey K. Brecht1, Mark A. Ritenour2, Charles A. Sims31Horticultural Sciences Department, University of Florida, Gainesville Florida 32611, United States of America2Indian River Research Education Center, University of Florida, Fort Pierce FL 34945, United States of America3Food Science Human Nutrition Dept., University of Florida, Gainesville FL 32611, United States of AmericaVIII International Postharvest Symposium