Combined effects of pH and sugar on growth rate of Zygosaccharomyces rouxii, a bakery product spoilage yeast

• Published in: Applied and environmental microbiology Vol. 65; no. 11; pp. 4921 - 4925
• Main Authors: Membre, J.M, Kubaczka, M, Chene, C
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.11.1999
• Subjects: acidity; Biological and medical sciences; Cereal and baking product industries; Ecology, environment; Food industries; Food Microbiology; Food Technology; Fundamental and applied biological sciences. Psychology; glucose; Glucose - metabolism; Hydrogen-Ion Concentration; Kinetics; Life Sciences; Models, Biological; sucrose; Sucrose - metabolism; Zygosaccharomyces - growth & development; Zygosaccharomyces rouxii; Bakery product; Microorganism growth; Sucrose; Prediction; Zygosaccharomyces rouxii; Environmental factor; Fungi; Non linear model; Concentration effect; Microorganism culture; pH; Ascomycetes; Bakery industry; Baker yeast; Biological contamination; Thallophyta
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/aem.65.11.4921-4925.1999

The effects of citric acid-modified pH (pH 2.5, 2.75, 3, 3.5, 4, 4.5, 5, and 5.5) and a 30% glucose-70% sucrose mixture (300, 400, 500, 600, 700, 800, 875, and 900 g/liter) on an osmophilic yeast, Zygosaccharomyces rouxii, were determined by using synthetic medium. One hundred experiments were carried out; 50-ml culture flasks were inoculated with 10(3) CFU ml(-1) by using a collection strain and a wild-type strain cocktail. The biomass was measured by counting cell colonies, and growth curves were fitted by using a Baranyi equation. The growth rate decreased linearly with sugar concentration, while the effect of pH was nonlinear. Indeed, the optimal pH range was found to be pH 3.5 to 5, and pH 2.5 resulted in a 30% reduction in the growth rate. Finally, we evaluated the performance of two nonlinear predictive models developed previously to describe bacterial contamination. Equations derived from the Rosso and Ratkowsky models gave similar results; however, the model that included dimensionless terms based on the Ratkowsky equation was preferred because it contained fewer estimated parameters and also because biological interpretation of the results was easier.