Potassium sorbate effects on citrus weight loss and decay control

• Potassium sorbate increases citrus weight loss in waxing and water dip treatments.
• Potassium sorbate eliminates the weight loss reduction capacity of all wax coatings.
• Potassium sorbate does not have good decay control in waxing treatments.
• Citrus leaves waxed using potassium sorbate quickly lose their fresh appearance.
• Potassium sorbate negative effects can be counteracted with ‘Fortisol’ biostimulant.

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.