Submitted to: Proceedings Florida State Horticultural Science
Publication Type: Proceedings
Publication Acceptance Date: June 1, 2004
Publication Date: N/A
Interpretive Summary: Postharvest losses of fresh citrus fruit result from pathological (decay) and physiological disorders. Exposing fresh fruit to mild heat treatments has been shown to reduce losses caused by decay and other postharvest disorders; however, there is the possibility of inducing heat injury to the fruit. We are interested in using heat treatment as a means of reducing postharvest losses of fresh grapefruit. We determined the effects of heating grapefruit with either liquid or water vapor heated to temperatures of 120 to 150 degrees Fahrenheit for up to two minutes. We found that holding fruit at higher temperatures for longer durations resulted more injury than hold fruit at lower temperatures for shorter durations. We also found that injury was reduced if the fruit were washed and waxed immediately following the heat treatment. The incidence of stem-end rots of grapefruit was reduced by several heat treatments; however, these treatments also resulted in injury to the grapefruit rind. Our results indicate that heat treatments do reduce the incidence of decay of grapefruit, but that heat injury can be a problem. In may be possible to combine a mild heat treatment with reduced rates of postharvest fungicides and thereby reduce losses.
Heat-treatments have been evaluated and utilized commercially to reduce postharvest decay, chilling sensitivity, and maintain quality of perishable horticultural products. Recent studies exposing grapefruit (Citrus paradisi Macf.) to short-duration, high-temperature water (e.g., 133 to 144 oF (56 to 62 oC) for 20 seconds) have shown promise at reducing subsequent development of mold (Penicillium) and increasing resistance to chilling injury (CI). Among the most prevalent citrus decay organisms in Florida are the stem-end rots (Diplodia natalensis and Phomopsis citri). Whereas Penicillium species invade citrus tissue through wounds, the stem-end rot organisms develop latent infections within the button tissue that are more protected from physical and chemical treatments. Here we report on efforts to identify heat-treatments that do not result in visible grapefruit peel injury, while reducing subsequent postharvest decay from natural infections. 'Marsh' or 'Ruby Red' grapefruit were exposed to liquid or vapor water at temperatures between 122 and 149 oF (50 to 65 oC) for 0 to 120 seconds. Fruit tolerance to heat injury followed a time x temperature relationship that usually shifted slightly between experiments. However, washing and waxing the fruit immediately after the heat-treatment greatly reduced the development of visible heat injury. Grapefruit could usually tolerate a 10-second exposure to 138 oF (59 oC) water, but extending exposure time to 120 seconds required lowering the temperatures to 127 oF (53 oC) to prevent peel injury. While some time x temperature combinations significantly reduced stem-end rot (SER), only once did an effective treatment not result in significant peel injury; In one experiment, hot water treatment of 138 oF (59 oC) for 10 seconds was noninjurious and resulted in about 90 percent reduction in SER incidence (to 3.5 percent). Injurious treatments were associated with elevated fruit respiration. Simulated commercial degreening conditions before or after the heat-treatments had no affect on the development of peel injury.