The Effect of Incubation Temperature on the Survival and Growth of Yeasts in Sethemi, South African Naturally Fermented Milk

• Published in: Food technology and biotechnology 2007-01, Vol.45 (1), p.21-26
• Main Authors: Kebede, A, Viljoen, B C, Gadaga, H, Narvhus, JA, Lourens-Hattingh, A
• Format: Article
• Language: English
• Subjects: Candida albicans; Debaryomyces hansenii; Kluyveromyces marxianus; lactic acid bacteria; naturally fermented milk; Saccharomyces cerevisiae; Sethemi; yeasts
• ISSN: 1330-9862; 1334-2606

The effect of temperature on the growth of yeasts during the production of Sethemi, South African naturally fermented milk (NFM), was studied by incubating raw milk and milk inoculated with selected yeast strains at 7, 15, 25 and 37 degree C. The different temperatures were selected to represent the average ambient temperatures around Bloemfontein, South Africa, during winter, spring, summer, and in the human body, respectively. The yeast strains used had previously been isolated from Sethemi and identified as Kluyveromyces marxianus, Saccharomyces cerevisiae, Candida albicans and Debaryomyces hansenii. The yeast strains were inoculated into raw milk separately and also as a mixture of the four strains. The yeast counts, lactic acid bacteria counts and pH were monitored over a period of 20 days. It was observed that although all the yeast strains grew in the milk at all temperatures, the fastest growth was at 37 degree C but there was a prolonged lag phase at 7 and 15 degree C. The highest yeast counts of 8.30 log (CFU/mL) were obtained at 25 degree C in the milk inoculated with K. marxianus. At all temperatures, the initial yeast count in the control was significantly (p