Food and Beverage Spoilage Yeasts

Abstract

Most people have very little knowledge or experience of yeasts; what experience they have is largely confined to the use of yeasts in bread-making or in alcoholic beverages, perhaps through home-brewing. It would surprise many people to realize that they also consume yeast cells daily, by the thousand, particularly in fresh fruit and vegetables. These yeasts are not likely to be the brewing or baking yeast, Saccharomyces cerevisiae, but are distributed widely across the 800 known yeast species (Barnett et al. 2000). Consumption of yeast cells in such numbers is not injurious to human health but part of a normal, healthy human diet. But if foods are not consumed but left to incubate at warm temperature, some of these yeasts will grow over time and cause a perceptible alteration in the food. Yeasts of such species may be termed food and beverage spoilage yeasts. Many excellent reviews of yeast spoilage have previously been published, including those of Ingram (1958), Walker and Ayres (1970), Davenport (1981), Fleet (1992), Tudor and Board (1993), Thomas (1993), Deak and Beuchat (1996) and Pitt and Hocking (1997). In these reviews, the literature of yeast spoilage is examined food by food, listing the yeasts found in and causing spoilage in each individual foodstuff, for example yeast spoilage in cereals; fruit juices and meat. There would therefore seem little need to recapitulate the information already published, in a further review. However, a number of recent technical innovations and social trends in food purchase and consumption made it timely to re-evaluate yeast spoilage in food. Firstly, DNA sequencing methods applied to yeast identification are revolutionizing the taxonomy and phylogeny of spoilage yeasts (James et al. 1996; Kurtzman and Robnett 1998, 2003). This has meant that very few of the species names associated with spoilage 50 years ago are currently recognized. Sequencing has also enabled a major reassessment of the relationships and phylogeny of many spoilage strains. This has resulted in amalgamation of certain genera and re-naming of others (Kurtzman Chapter 11