39F-8

R. M. GOODRICH, Citrus Research & Education Center, University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850 and J. A. Narciso.

Common citrus industry practice has been to utilize orange serum agar (OSA) and acidified potato dextrose agar (APDA) to recover and enumerate aciduric bacteria and fungi from citrus products. Industrial collection of this data is important for quality control, purchase specifications, process control, system validation and shelf life determination. Yeasts such as Saccharomyces cerevisiae and Zygosaccharomyces spp. continue to impact the industry, and, at times, cause economic loss due to spoilage and substandard quality. For this reason, research was initiated to evaluate the efficacy of current methodology (plating with APDA) and to assess other potential methods to evaluate yeasts in citrus products (primarily juices).

Experiments were conducted with microorganisms collected from citrus processing environments and products and with microorganisms purchased from a commercial culture collection. Various commercial and custom-blended media were screened for efficacy in supporting yeast growth while concurrently inhibiting aciduric bacterial growth. Combining performance and ease of preparation into an overall score (OS) with higher numbers more favorable, experiments indicated OSA + chloramphenicol (OSAC)=OSA + neomycin (OSAN) > OSA + chloramphenicol + neomycin (OSACN) > potato dextrose agar (PDA) > APDA. Screening of a wide variety of both cultured and wild type yeast showed OSAC was a suitable medium for isolating and enumerating yeasts from citrus products.