Zygosaccharomyces lentus: a significant new osmophilic, preservative-resistant spoilage yeast, capable of growth at low temperature.

Zygosaccharomyces lentus is a yeast species recently identified from its physiology and 18S ribosomal sequencing (Steels et al. 1999).The physiological characteristics of five strains of this new yeast so far isolated were investigated, particularly those of technical significance for a spoilage yeast, namely temperature range, pH range, osmotolerance, sugar fermentation, resistance to food preservatives such as sorbic acid, benzoic acid and dimethyldicarbonate (DMDC; Velcorin). Adaptation to benzoic acid, and growth in shaking and static culture were also investigated. Zygosaccharomyces lentus strains grew over a wide range of temperature (4-25 degrees C) and pH 2.2-7.0. Growth at 4 degrees C was significant. Zygosaccharomyces lentus strains grew at 25-26 degrees C in static culture but were unable to grow in aerobic culture close to their temperature maximum. All Z. lentus strains grew in 60% w/v sugar and consequently, are osmotolerant. Zygosaccharomyces lentus strains could utilize sucrose, glucose or fructose as a source of fermentable sugar, but not galactose. Zygosaccharomyces lentus strains were resistant to food preservatives, growing in sorbic acid up to 400 mg l-1 and benzoic acid to 900 mg l-1 at pH 4.0. Adaptation to higher preservative concentrations was demonstrated with benzoic acid. Resistance to DMDC was shown to be greater than that of Z. bailii and Saccharomyces cerevisiae. This study confirms that Z. lentus is an important food spoilage organism potentially capable of growth in a wide range of food products, particularly low pH, high sugar foods and drinks. It is likely to be more significant than Z. bailii in the spoilage of chilled products.