Growth of fermentative and non-fermentative yeasts in natural yoghurt, stored in polystyrene cartons.

Permeation of oxygen through polystyrene packaging is a factor in the growth of yeasts in natural yoghurt. Diffusion of oxygen through the packaging material can permit the growth of non-fermentative yeasts in yoghurt stored at refrigeration temperatures. Yarrowia lipolytica, a non-fermentative yeasts which does not utilize lactose was isolated from yoghurt. The growth in natural yoghurt of Yarrowia lipolytica and the lactose-fermenting yeast Kluyveromyces marxianus was investigated. Both yeasts grew in yoghurt with reduced fat content. Storage of yoghurt in an anaerobic atmosphere eliminated growth of Yarrowia lipolytica but permitted fermentative growth of Kluyveromyces marxianus.