Spoilage yeasts in foods and beverages: characterisation and ecology for improved diagnosis and control

Abstract

Foods and drinks with high solute concentration (fruit juices and concentrates, marzipan, salted and dry-cured meats, olives and cheeses), and foods containing preservatives (wine, beverages and sauces) were selected in order to characterise the contaminant yeast flora by rapid typing techniques. These included the testing of several types of molecular methods (e.g. RFLP, DNA-fingerprinting, PCR-based techniques), analysis of long-chain fatty acids and of isoenzymes. The PCR-based detection methods enabled a faster detection of emerging specific spoilers at earlier stages of processing. Fatty acid characterisation allowed the assessment of the most frequent types of contamination yeasts and supplied the information for the definition of relevant zymological indicators. A selected group of strains was used for further studies of mechanisms underlying the resistance/tolerance of yeasts towards preservatives (weak acids) and other stress factors (temperature, high sugar and salt concentrations). This study enabled the acquisition of data on the basic biology of yeasts used in the development of differential and selective media for Zygosaccharomyces bailii, Yarrowia lipolytica, Kluyveromyces marxianus and Dekkera sp.