Biocontrol of spoilage yeasts and moulds by Williopsis saturnus var. saturnus in yoghurt

Spoilage due to yeast and mould growth is a major issue for yoghurt quality and shelf‐life. There is a need to develop natural alternatives to chemical preservation. The purpose of this paper is to determine the effectiveness of mycocinogenic yeast Williopsis saturnus var. saturnus as a biocontrol agent against spoilage yeasts and moulds in plain yoghurt.

Yoghurts were prepared from reconstituted skim milk and were challenged with spoilage yeasts and moulds. The treatment contained the added mycocinogenic yeast and the control without. All yoghurts were incubated at 30^○C. Yeast and mould growth were determined by observing gas formation and mould colony occurrence at regular intervals.

W. saturnus var. saturnus inhibited growth of lactose‐fermenting and galactose‐fermenting yeasts (Candida kefir and Kluvyveromyces marxianus), and lactose non‐fermenting but galactose fermenting yeasts (strains of Saccharomyces cerevisiae and Saccharomyces bayanus). The yeast also inhibited growth of dairy moulds including Byssochlamys, Eurotium and Penicillium.

The inhibition of this mycocinogenic yeast against yeasts and moulds was dependent upon the concentration of the latter. Thus, hygiene and good manufacturing practice are essential in order to keep the contaminant load down and to ensure the effectiveness of the mycocinogenic yeast.

The use of mycocinogenic yeast to control spoilage yeasts and moulds in yoghurt is a novel approach with a potential to minimise yoghurt spoilage and extend the shelf‐life of yoghurt.