1a. Objectives (from AD-416):
Objective 1. Develop integrated and commercially feasible pre-harvest practices and treatments to maintain quality and extend the shelf and shipping life of fresh fruit (primarily citrus fruit and table grapes). Objective 2. Develop integrated and commercially feasible postharvest practices and treatments to maintain quality and extend the shelf and shipping life of fresh fruit (primarily citrus fruit and table grapes).
1b. Approach (from AD-416):
A variety of preharvest and postharvest actions and chemical treatments to extend the shelf life and maintain quality of fresh citrus fruit and table grapes will be developed and evaluated under laboratory and semi-commercial conditions. Promising treatments will be combined in integrated regimes later in this project. Replacing 5302-43000-035-00D (9/2010).
3. Progress Report:
Off-flavor formation in ‘Owari’ Satsuma mandarins during storage was found to be dependent on time of harvest, with fruit harvested in late November developing the greatest amount of off-flavor. The off-flavor development was accompanied by a reduction in internal oxygen and an enhancement in ethanol and ethyl ester concentration. Comparisons were made between ‘Pixie’ and ‘Gold Nugget’, two mandarin varieties that differ greatly in ethanol production during storage. “Pixie’, the high ethanol producer, developed more off-flavor than ‘Gold Nugget’, the low ethanol producer, indicating that ethanol accumulation is related to off-flavor development. Assays of alcohol dehydrogenase indicated that ‘Pixie’ had substantially higher activity than ‘Gold Nugget’ and may be part of the reason for the difference in ethanol accumulation. It was also found that ‘Pixie’ has a greater propensity for fermentation and ethanol production due to a low permeability of the peel to oxygen. Postharvest decay annually causes significant losses of fresh citrus fruit and table grapes. Control of postharvest green mold of citrus caused by the fungal decay pathogen Penicillium digitatum is needed to successfully store, transport, and market these fruit. Infections occur primarily through superficial wounds inflicted on the fruit during harvest and handling operations, sometimes, one or two days elapse before the fruit pass down packinglines where antifungal treatments can be applied to manage this problem. Because managers do not know the influence of the length of this interval on the effectiveness of the packline treatments to control this pathogen, a series of experiments were conducted where the fruit were inoculated and stored at a range of temperatures before they were treated. The tests were done under controlled laboratory conditions and repeated in three commercial packinghouses. The typical packinghouse treatment sequence, developed in part from earlier work at this location, included immersion in heated sodium bicarbonate solution, passage through a heated, dilute solution of the fungicide imazalil, and lastly coated with a fruit wax containing this fungicide and a second fungicide, thiabendazole. Under conditions that were relatively temperate (15 to 20 C), an interval of 48 hours could elapse before treatment and green mold was well controlled. Under cold conditions (5 C), an interval of 96 hours could elapse before treatment and green mold was well controlled. A practical conclusion of this work is that when harvest occurs during warmer periods, proper management of the fruit indicates they should be processed within 48 hours of harvest. When harvest occurs during colder, winter conditions, the fruit should be processed within 96 hours of harvest.
1. Reasons for differences in off-flavor development among mandarin varieties. Mandarins are increasingly popular with consumers but have a problem in that they often develop off-flavors in storage. ARS researchers at Parlier, California, in collaboration with researchers from the University of California, compared two mandarin varieties that differ greatly in their production of ethanol and other off-flavor compounds after packing. It was found that high production of these compounds was associated with a lesser ability of oxygen and other gases to pass through the peel and with a higher enzymatic activity for ethanol production. This information on what properties of the fruit determine off-flavor occurrence in mandarins can be used to better understand why fruit sometimes produce off-flavors and to develop new varieties that maintain good flavor quality throughout storage.
Smilanick, J.L., Mlikota Gabler, F., Margosan, D.A. 2012. Evaluation under commercial conditions of the application of continuous, low concentrations of ozone during the cold storage of table grapes. Acta Horticulturae. 945:357-361.