Detection of preservative-resistant Zygosaccharomyces bailii
1998
Beuchat, L.R. (University of Georgia, Griffin (USA). Center for Food Safety and Quality Enhancement)
Zygosaccharomyces bailii is a major spoilage yeast in acidic foods, having strong fermentative activity and the ability to grow in hostile environments containing relatively high concentrations of food preservatives such as benzoic and sorbic acids. Its presence in non-pasteurized fruits and fruit concentrates, purees, syrups and juices is of concern when these products are used as ingredients in dairy products. Spoilage of yoghurt and speciality cheeses, for example, can occur when fruit products containing Z. bailii are combined during formulation or processing. Malt extract agar supplemented with 0.5 per cent acetic acid is generally recommended for selection of preservative-resistant Z. bailii. However, other acid-tolerant yeasts such as Pichia and Schizosaccharomyces species will also grow on this medium. We evaluated 31 formulations of media for their efficacy in detecting and enumerating temperature-stressed and healthy cells of Z. bailii in foods. Overall, the performance of acidified tryptone glucose yeast extract agar was mdged to be best. However, the suitability of this and other test media, including acidified malt extract agar, in inhibiting non-stressed yeasts other than Z. bailii is less than optimum. Additional work is required to develop a medium that will exclusively select for preservative-resistant Z. bailii.
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