ABSTRACT
Yeast have been isolated from all kinds of dairy products (Fleet 1990; Fleet and Mian 1987; Jakobsen and Narvhus 1996; Rohm et al. 1992; Tilbury et al. 1974). Yeast are used as important starter cultures in food products such as bread, beer, wine, traditional fermented foods (Fleet 1990; Fleet and Mian 1987; Jakobsen and Narvhus 1996) and seems to be the most important micro-organism exploited by man. The role of yeast as micro-organisms, which could have a positive influence on the quality of dairy products, especially cheese, has not been widely accepted (Fleet 1990; Jakobsen and Narvhus 1996). Instead, yeasts have often been seen as spoilage organisms originating from poor hygiene and sanitation (Fleet and Mian 1987; Jakobsen and Narvhus 1996). The nutritional requirement of yeast, the ability to grow at low temperature, low pH, low moisture content, and high salt or sugar concentrations together with their enzymatic activity make yeast a natural part of the microbiota in dairy products. In 1995 the first symposium on “Yeasts in the dairy industry: Positive and Negative Aspects” was organized and held by the International Dairy Federation (IDF) expert group F47-Yeast. As reflected in the published literature the interest in yeast in the dairy industry has increased since and the knowledge of the positive and negative role played by yeast in dairy products has become more detailed. The key areas have been: (a) study of important technological characteristics of yeast, e.g., proteolytic and lipolytic activity, aroma formation and fermentation and/or assimilation of residual sugars and lactate and citrate and pigment formation especially related to different kind of cheese; (b) properties affecting both the negative role of yeast as spoilage organism causing quality defects as well as the potential of yeast as highly controlled starter cultures; (c) yeast classification and taxonomy based upon molecular methods. The present review will deal with the positive and negative aspects of yeast in the dairy industry.
