Environmental Factors Affecting Yeasts

Introduction
Yeasts are a Leading cause of spoilage of yogurt, doogh and fermented milks in which the low pH provides a selective environment for their growth (Fleet, 1990; Rohm, Eliskasses, & Bräuer, 1992; Hansen and Jakobsen, 2004). Yogurts and doogh having initial counts of >100 CFU/g tend to spoil quickly. Yeasty and fermented off-flavors and Swelling of the doogh and yoghurt package are often detected when yeasts grow to 105–106 CFU/g (Fleet, 1990). Green and Ibe (1986), Viljoen et al (2003) examined yoghurt samples from which species of Kluyveromyces marxianus, Saccharomyces cerevisiae and Rhodotorula glutinis were Dominant isolated. The yeasts may also develop on the surfaces of production equipment, such as mixing vessels and filling machines, that have been poorly cleaned and sanitized (Davis, 1970, 1975; Suriyarachchi and Fleet, 1981;
It was recently reported that benzene can be formed from benzoic acid in foods (United Kingdom Food Standards Agency, 2006; Federal Institute for Risk Assessment, 2005). Yeasts include S. cerevisiae and P. anomala are able to decarboxylate sorbic acid to 1, 3-pentadiene causing a kerosene-like off-odour (Stratford et al., 2007) and S. pombe may produce off-flavours if sulphite is present. Such problems with chemically synthesized preservatives and the growing demand of consumers for natural food additives have turned attention to plant-derived natural antimicrobials such as essential oils (EOs) and