Growth and survival of a probiotic yeast in dairy products

Poor survival of probiotic bacteria in yogurt has been recorded. Growth of a probiotic yeast, Saccharomyces boulardii, in association with the bio-yogurt microflora, by incorporating the yeast into commercial bio-yogurt, has been suggested to stimulate the growth of the probiotic organisms and to assure their survival during shelflife. Therefore, the ability of growth and survival of the probiotic yeast itself in diary products, namely bio-yogurt, UHT yogurt and UHT milk were investigated. S. boulardii was incorporated into the dairy products and stored at 4 degreesC over a 4-week period. pH, Lactose utilisation and the production of organic acids were monitored at each interval. Based on the results in this study, the probiotic yeast species, S. boulardii, has the ability to grow in bio-yogurt reaching maximum counts exceeding 10(7) cfu/g. The number of yeast populations was substantially higher in the fruit based yogurt, mainly due to the presence of proportions of sucrose and fructose derived from the fruit. Despite the inability of S. boulardii to utilize lactose, the yeast species utilized available organic acids, galactose and glucose derived from bacterial metabolism of the milk sugar lactose present in the dairy products. Excessive gas and alcohol production by the yeast species proved, however, to be major constraints for incorporating this yeast into bio-yogurt. (C) 2001 Elsevier Science Ltd. All rights reserved.