SHELLAC COATINGS FOR GRAPEFRUITS THAT FAVOR BIOLOGICAL-CONTROL OF PENICILLIUM-DIGITATUM BY CANDIDA-OLEOPHILA

Shellac coatings that support significantly high populations of the ye ast Candida oleophila for biocontrol of Penicillium digitatum were for mulated for postharvest application to grapefruits. An aqueous shellac latex was not toxic to the yeast and was suitable for testing constit uents of commercial shellac coatings. Alteration of this product to co ntain 2% ethanol was nontoxic, but 4, 6, 8, and 10% ethanol killed 90 of the yeast cells within 24, 4, 2, and 0.5 h, respectively. Above a p H of 8.25, cell death was rapid when amine bases were incorporated. Th is level of toxicity resulted from addition to the shellac latex of mo re than 1.5% morpholine or 0.3% ammonia; a similar death rate develope d nearer to pH 9.0 with incorporation of approximately 1.5% KOH. Altho ugh higher concentrations of base were required for the preparation of experimental formulations derived from bleached shellac, shellac este r, and wood resin ester, the relationship between the pH of the liquid coating and yeast survival persisted. Particularly with wood resin es ter, KOH solutions maintained higher populations of yeast. When applie d to grapefruits postharvest, a shellac latex formulation and a dissol ved shellac/shellac ester formulation supported surface populations of yeasts between 10(4) and 10(5) CFU/cm(2) throughout 4 months of stora ge at 13 degrees C, These preparations significantly improved shelf-li fe when compared to fruits coated with a commercial shellac formulatio n. (C) 1996 Academic Press, Inc.