Postharvest Biology and Technology 96 (2014) 7–13
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Potassium sorbate effects on citrus weight loss and decay control Javier Parra ∗ , Gabriela Ripoll, Benito Orihuel-Iranzo ∗ Department of Postharvest Technology, Productos Citrosol S.A., Partida Alameda parcela C, 46721 Potries, Valencia, Spain
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Article history: Received 7 February 2014 Accepted 26 April 2014 Keywords: Potassium sorbate Penicillium digitatum Citrus fruit Wax Weight loss Decay control
a b s t r a c t Potassium sorbate (PS) is a well-known and widely used food preservative. Among other applications, it is used as a GRAS fungistatic postharvest treatment for citrus, although its use is not free of significant adverse effects. In this paper, we study in detail the efficacy of wax containing increasing concentrations of PS to control Penicillium digitatum decay in citrus fruit, and its effect on fruit weight loss. Decay control and weight loss increased with the concentration of PS in the wax. Wax with typical amounts of 2–5% PS showed poor decay reduction indices (DRI), between 26% and 32%, whereas fruit weight loss increased compared with non-waxed controls. Waxing of fruit reduced weight loss by up to 40%, depending on wax formulation, but the addition of just 2% PS to the wax caused an increase in fruit weight loss of up to 65% compared with the waxed fruit. Similar results were observed for all the types of wax formulations tested. The hygroscopic effects of PS are even more damaging for citrus fruit with leaves. The leaves lose weight very rapidly when PS is added to the wax and they become desiccated in 24 h. We also present the results of a similar study where PS was applied to citrus as an aqueous treatment. When applied in water, PS was far more effective for decay control than when applied in wax, but there was also a considerable increase in fruit weight loss. A treatment combining aqueous PS with Fortisol® Ca Plus biostimulant completely solved the problem of weight loss, these mixtures being commercially feasible treatments. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Citrus fruit are prone to postharvest decay, and although transport and storage conditions of fresh citrus have improved, mainly because of the use of refrigerated transport and cold rooms (Korsten, 2006), fungal diseases still produce significant economic losses (Smilanick et al., 2006). As a result of the big increase in citrus sold in pre-packings, i.e. in nets that sometimes contain up to 35 fruit, where just one decayed fruit can contaminate or cause decay in the whole package, citrus decay control has now become a harder task than in the past. In this scenario, the postharvest use of synthetic fungicides such as imazalil, ortho-phenylphenol, thiabendazole, or pyrimethanil, among others, is still the most effective way to achieve mold control in citrus fruit (Ismail and Zhang, 2004). Green mold, Penicillium digitatum, and blue mold, P. italicum, are the major fungal pathogens that cause decay in citrus fruit in Spanish citrus shipments (Tuset, 1987), and in all citrus when grown in low summer rainfall areas (Palou et al., 2008b). It is well known that the highest efficacy in postharvest citrus decay control is achieved
∗ Corresponding authors. Tel.: +34 96 280 05 12; fax: +34 96 280 08 21. E-mail addresses: jparra@citrosol.com (J. Parra), borihuel@citrosol.com (B. Orihuel-Iranzo). http://dx.doi.org/10.1016/j.postharvbio.2014.04.011 0925-5214/© 2014 Elsevier B.V. All rights reserved.
when the treatment is applied promptly after harvest (Chitzanidis, 1986; Wild and Spohr, 1989; Brown, 1999), usually as an aqueous treatment applied by drenching or water tank dipping. This first treatment is usually complemented by a second treatment on the packing line, commonly with wax containing fungicides. However, because of reports about the deleterious effects of some synthetic chemicals on the environment and even on the health of consumers, there is a demand for the commercialization of chemical-free fruit. Fungicide-free decay control methods are needed, and treatments based on low-toxicity compounds could be a suitable alternative. These chemicals should have high decay control efficacy with minimal toxicity and environmental impact (Palou et al., 2008b). The main low-toxicity chemical alternatives for citrus decay control are food additives (Palou et al., 2002b), inorganic salts (Palou et al., 2002a; Deliopoulos et al., 2010; Youssef et al., 2012b; Cerioni et al., 2013a,b), essential oils (Plaza et al., 2004; du Plooy et al., 2009; Combrinck et al., 2011; Perez-Alfonso et al., 2012; Castillo et al., 2014) and phytochemicals (Hao et al., 2010). Among the food additives, potassium sorbate (E-202), PS, is a widely used broad spectrum food preservative (Sofos, 1989; Stopforth et al., 2005). In 1978, it was first proposed to be used in citrus decay control of P. digitatum (Smoot and McCornack, 1978). Since then, aqueous PS has been described many times as an alternative