Description

Abstract: Dilution plating techniques are designed to determine populations of viable fungal propagules per unit weight or volume of food. Direct plating techniques, on the other hand, are designed to assess the internal mycoflora of individual pieces of foods, e.g., seeds or dried fruits, and results are expressed as a percentage of infected pieces. Both techniques are used by industry and regulatory agencies to monitor levels of fungal contamination at various stages of food handling, storing, processing and marketing. Peptone (0.1%) water is commonly used as a diluent for samples to be homogenized or blended. Buffered diluents containing up to 30% glucose are sucrose are recommended for enumerating xerophiles. No one medium is satisfactory for detection or enumeration of yeasts and moulds in all foods. Dichloran rose bengal chloramphenicol agar, oxytetracycline glucose yeast extract agar and rose bengal chloramphenicol agar are superior to acidefied potate dextrose agar for enumeration of yeasts and moulds. Dichloran 18% glycerol agar performs well for enumerating moderating moderately xerophilic yeasts and moulds. Fastidous xerophiles require media containing high concentrations of sugars and/or sodium chloride. Media have been formulated to detect potentially aflatoxigenic aspergilli and mycotoxigenic strains of penicillia and fusaria, but increased selectivity and specificity of media for detecting mycotoxigenic moulds are needed. Heat-resistant mould ascospores often require heat treatment prior to plating in order to activate the fermination process. The spread-plate technique is strongly preffered over the pour-plate technique for enumeratingyeasts and moulds. The recommended incubation temperature is 25