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Title: A new composite coating containing HPMC, beeswax and shellac for 'Valencia' oranges and 'Marisol' tangerines

item Goodner, Kevin
item Plotto, Anne

Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2007
Publication Date: 3/20/2008
Citation: Navaro-Tarazaga, M.-L.,Perez-Gago, M.-B., Goodner, K., Plotto, A. 2007. A new composite coating containing HPMC, beeswax and shellac for 'Valencia' oranges and 'Marisol' tangerines. Proceedings of Florida State Horticultural Society. 120:228-234.

Interpretive Summary: Citrus fruit require waxing to minimize water loss and shriveling in storage. Commercial waxes (coatings) used for citrus include carnauba and shellac, which provide an attractive shine to the fruit, but are not necessarily made of 100% food grade ingredients, or ingredients that would be considered acceptable for organic food. This study presents two experiments designed to optimize the formulation of a composite (made of lipid- and carbohydrate-type ingredients) edible coating, and the coating effect on water loss, shine, fruit respiration (or gas permeability), volatile compounds and sensory qualities. The coating was applied on 'Valencia' oranges and 'Marisol' tangerines. The experimental coating was made of hydroxypropylmethylcellulose (HPMC), bee's wax, shellac, oleic acid (a lipid) and glycerol (a plasticizer). The optimum performance was with a formulation where the HPMC:glycerol ratio was 1:2, with 8% solids content. Another experimental formulation made with a mixture of polyethylene and candellila wax gave the best results in terms of fruit quality in storage.

Technical Abstract: Commercial coatings used for citrus fruit include carnauba and shellac waxes or resins, which provide an attractive shine to the fruit, but are not necessarily made of 100% food grade ingredients. A new food grade formulation based on bee's wax (BW), shellac resin and hydroxypropylmethylcellulose (HPMC) was tested, along with an experimental polyethylene-candellila (PE) wax emulsion, and two commercial citrus coatings (shellac and carnauba based). 'Valencia' oranges from a local grove were washed, hand-coated, dried, and stored 2 weeks at 23-25 °C. The PE and carnauba coatings provided the best weight loss control, and were preferred for appearance by a sensory taste panel. The HPMC-based coating exhibited the least shine, and was rated similar to control for appearance. On the contrary, shellac-coated fruit were the shiniest, but had intermediate appearance preference ratings. Shellac coated fruit had high levels of ethanol and CO2, followed by HPMC-coated fruit. These indicators of anaerobiosis are known to produce off aromas. Volatiles analysis showed that ethanol, methanol, ethyl actetae, and hexanal were high in shellac-coated fruit, while uncoated oranges had higher levels of volatile compounds that characterize fresh citrus flavor. The HPMC formulation was modified to increase permeability to O2 and CO2 and was tested on 'Marisol' tangerines from Spain, and stored at 23 °C for 1, 2, and 3 weeks. A reduction of the HPMC:glycerol ratio from 2:1 to 1:2 improved gas permeability and sensory quality of tangerines stored 1 and 2 weeks at room temperature. Increasing solid content (SC) from 5% to 8% reduced weight loss. Therefore, the HPMC formulation with HPMC:glycerol ratio of 1:2 and at 8% SC was retained for further applications with tangerines.