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Yeasts isolated from ‘Kwerionik’ and some of their biological attributes of importance in milk fermentation




‘Kwerionik’ is a traditional cultured milk produced in Eastern Uganda at the slopes of Mount  Elgon. Field and laboratory fermented ‘Kwerionik’ samples were microbiologically analysed to establish the levels of yeast strains at the various stages of fermentation. Also yeast isolates were identified to species level and their important characteristics for milk fermentation were identified.  Yeast enumeration and isolation were carried out on Potato Dextrose agar under aerobic conditions fort 30°C for two days.  Presence of yeasts was confirmed by colonial morphology and by microscopy.  The isolates were screened into groups by polymerase chain reaction-intergenic transcribed spacer (PCR-ITS) fragment length polymorphism (18S-28S), and the various groups were identified to genus and species level by the carbohydrate assimilation tests using the ID32C kit (bioMérieux, Marcy l’Etoile, France). Other biochemical tests including ability to assimilate lactic acid and citric acid and  to ferment carbohydrates ( glucose, galactose, lactose, sucrose, maltose and raffinose) and enzymatic activity were also carried out.  Isolates belonging to the same ITS group were distinguished  by API ID32 kit and species identity was confirmed using Candida krusei species specific PCR .  A total of 261 yeast isolates were analysed and the predominant species included Candida krusei (52.1%), Candida kefyr (26.8%).  Others were Pichia ohmeria (5.8%), Candida intermedia or Candida lusitaniae (5%), Candida pelliculosa (2.7%), Candida lambica (3.1%), Candida guilliermondii (1.5%) and Candida holmii (0.9%).  Some of the species exhibited properties important to fermentation of milk, such as, β-galactosidase, lipase and proteolytic activity.  The contribution of the yeasts to ‛Kwerionik’ fermentation needed to be established.