2012 Annual Report
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.
Twenty-seven mandarin varieties were screened for the ability to produce ethanol after application of a wax coating. A further test performed the same assay on a population of 31 mandarin hybrids from a cross of ‘Fortune’ and ‘Fairchild’. In both experiments ethanol productions was highly variable across host genotype and was linked with carbon dioxide content in the fruit. Ethanol production is linked to the formation of off-flavor in mandarins and further work to determine the causes of the varietal differences in ethanol accumulation could lead to the development of mandarins with minimal off-flavor problems following storage. Additional experimentation to examine postharvest flavor changes in 5 mandarin varieties found flavor loss to occur following storage of from 1 to 4 weeks, with the most severe impact on flavor occurring in fruit stored at room temperature. Sensory research performed with avocados indicated flavor was unaffected by whether or not the fruit were ripened prior to the initiation of cold storage.
Postharvest decay causes significant annual losses of fresh citrus fruit and table grapes. Control of postharvest citrus diseases by fungicides has been compromised by the development of resistance in the fungal decay pathogen Penicillium digitatum. A brief postharvest treatment with heated potassium phosphite was shown to effectively control postharvest decay of citrus alone, and improved the activity of fungicides when mixed with the fungicide. This practice also reduced fungicide-resistant populations of the pathogen.
Reducing phosphite pH increased its inhibitory activity and enhanced residue persistence. Phosphite did not harm fruit quality and did not alter the natural change of green rind color to orange or yellow as the fruit aged. Preharvest applications of chitosan formulations applied directly to clusters of table grapes altered their physiology and modestly reduced subsequent decay (mostly caused by Botrytis cinerea) during storage. No chitosan formulation harmed berry quality, and all increased endochitinase activity and decreased berry hydrogen peroxide content. One of the chitosan formulations increased quercetin, myricetin, and resveratrol content of the berry skin. Under environmental conditions that simulated cold storage of table grapes, the mortality rate of seven common decay fungi was determined in a low concentration (0.1 ppm) of ozone gas shown in prior work to prolong fruit storage life. Fungi exposed to these conditions died within several weeks, while in cold air alone they survived several months.
Ethanol production varies greatly among mandarin varieties that have been waxed. Mandarins are increasingly important to the California citrus industry but often develop off-flavors in storage. ARS Researchers in Parlier, California, in collaboration with researchers from the University of California, screened 27 mandarin varieties and 31 mandarin hybrids for ethanol production after the application of wax during packing. Large differences were present among the varieties and hybrids in the amount of ethanol that accumulated during storage. Since off-flavor production is linked to the formation of ethanol, these differences can be used to better understand why fruit sometimes produce off-flavors and to develop new varieties that maintain good flavor quality throughout storage.
Erasmus, A., Lennox, C., Hennie, J., Smilanick, J.L., Keith, L., Fourie, P. 2011. Imazil residue loading and green mold control in south african citrus pack-houses. Postharvest Biology and Technology. 62(2):193-203.
Obenland, D.M., Collin, S., Sievert, J., Arpaia, M. 2012. Influence of maturity and ripening on aroma volatiles and flavor in avocado. Postharvest Biology and Technology. 71:41-50.