Development of a novel soy-wax containing emulsion with enhanced antifungal properties for the postharvest treatment of fresh citrus fruit

A novel single pendent hydroxy functionalized soy-wax was synthesized via hydroboration-oxidation of high oleic soybean oil (HBO-HOSO). Low apparent viscosity emulsions containing such wax was formulated as an alternative to the high-cost carnauba wax (CAR) and resin-based emulsions used in citrus fruit coatings, mainly to impart sheen and prevent moisture loss. The effect of additional CAR on properties of HBO-HOSO emulsions was analyzed, and the performance of the optimal formulation for citrus coating was evaluated. Addition of CAR to HBO-HOSO led to an increase in apparent viscosity, although reduced the particle size of the emulsion. An emulsion containing 20% HBO-HOSO of total solid content resulted in a low apparent viscosity and small particle size, comparable to commercial emulsions made from CAR (O-Wax and ORO), oxidized polyethylene (LS-Wax) and shellac resin (STAR). Adherence of coatings made with HBO-HOSO to the fruit surface was not significantly different compared to commercial benchmarks. The HBO-HOSO-containing emulsion provided similar gloss and resulted in reduced moisture loss (6.0%) compared to the commercial products (7.0-14.6%). HBO-HOSO-containing emulsions also did not affect the release of imazalil, a common fungicide applied on citrus fruits, and simultaneously more effectively inhibited the growth of Aspergillus niger (ATCC 16888).