miércoles, marzo 20, 2002

From spoilage to probiotic: the new role of yeast in dairy products

Foodinfo Online FSTA Reports -->19 March 2002

Probiotic microorganisms are increasingly added to foods to promote the maintenance of a healthy balance of gastrointestinal microflora. The most frequently used microorganisms are lactobacilli and bifidobacteria, which are often added to fermented dairy products, particularly yoghurts. However, the potential role of yeasts as probiotic agents has not been fully investigated, despite the fact that yeasts form an integral part of the microflora of many dairy-related products. Starter cultures containing yeasts and bacteria are used in the preparation of some fermented milk products, including kefir, koumiss and laban, and several antagonistic reactions have been observed between yeasts such as Saccharomyces cerevisiae and enteric pathogens, such as Escherichia coli and Salmonella and Shigella species. However, yeasts are frequently associated with the spoilage of the final product, causing alcoholic fermentation and gas formation in yoghurts containing added fruit and sucrose. The yeast Saccharomyces boulardii was first isolated from lychees in the 1950s and has since been used in the prevention and treatment of diarrhoeal diseases. A study by Laurens-Hattingh et al.1 reports on the ability of S. boulardii to grow in bio-yoghurt, UHT-treated yoghurt and UHT-treated milk, in order to determine at a later stage the effect on survival of Lactobacillus acidophilus and Bifidobacterium bifidum during shelf life. Previous studies have shown that survival of L. acidophilus and B. bifidum is poor in yoghurts, due to their low acid tolerance. Since yeasts are able to utilize organic acids and increase the pH of the environment, addition of yeasts to bio-yoghurts may enhance the stability of their probiotic bacteria.
1Lourens-Hattingh A; Viljoen BC (2001). Growth and survival of a probiotic yeast in dairy products.
Food Research International 34 (9) 791-796.
An abstract of this paper can be found in Food Science and Technology Abstracts, citation reference 2001-12-Pl1955.

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