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Novel approaches for postharvest preservation of fresh citrus fruits

Abstract:

Citrus are nonclimacteric fruits that are harvested when their commercial maturity index has already been reached. The maturity index expresses the relationship between two important internal quality parameters, solid soluble concentration and titratable acidity, that determine the fruit consumer's acceptance. These values are not dependent on postharvest external quality attributes and, for instance, fully-ripened fruit may still have green-colored rind. For this reason early mandarins or lemons may be artificially degreened through treatments with exogenous ethylene. Postharvest handling in citrus packinghouses, including degreening, packingline procedures, cold storage, or other treatments, are intended to commercialize fruit of maximum quality, increase their postharvest life, and reduce produce losses. According to their origin, major postharvest losses are caused by weight loss, physiological disorders, biotic diseases, and quarantine pests. Conventional synthetic waxes, often amended with chemical fungicides, other specific treatments with conventional synthetic fungicides, or in-transit cold treatments against quarantine fruit flies have been used for many years by the export citrus industry to minimize postharvest losses. However, with the repeated use of these practices important problems have arisen that increasingly limit the profitable commercialization of fresh citrus fruits. These problems include, for example, health and environmental issues associated with conventional waxes containing ammoniacal compounds or synthetic fungicides like imazalil, thiabendazole or sodium ortho-phenyl phenate that generate chemical residues and lead to the proliferation of pathogenic resistant strains. Furthermore, lengthy standard cold treatments are not appropriate for mandarin cultivars susceptible to chilling injury. There is, therefore, an increasing need to find and implement alternatives to these traditional postharvest procedures. In this chapter, novel approaches for postharvest preservation of fresh citrus fruits are reviewed. Substantial progress has been accomplished in evaluating new effective postharvest disease control methods as part of integrated disease management programs. New active ingbkp_redients such as pyrimethanil, fludioxonil, azoxystrobin or trifloxystrobin, classified as reduced risk fungicides; low-toxicity or natural antifungal chemicals such as food additives, generally regarded as safe compounds, or essential oils have been tested alone or in combinations against the most important citrus postharvest diseases worldwide, namely green and blue molds and sour rot, caused by Penicillium digitatum, Penicillium italicum and Geotrichum citri-aurantii, respectively. The development of composite natural edible coatings to substitute conventional citrus waxes or, in the case of incorporating low-toxicity antifungal ingbkp_redients, to replace also the use of synthetic fungicides, is currently an active research field. Likewise, attention has been devoted to the evaluation of methods alternative to the mandatory cold exposure for the control of important citrus quarantine pests such as the Mediterranean fruit fly Ceratitis capitata. Such alternatives include heat, insecticidal controlled atmospheres, ionizing radiation (γ-, β-, X-rays) and combinations of these treatments. © 2011 by Nova Science Publishers, Inc. All rights reserved.