Enhancing stability of lactic acid bacteria and probiotics by Williopsis saturnus var. saturnus in fermented milks

There is a need to improve stability of lactic acid bacteria (LAB) and probiotics in fermented milks especially at elevated temperatures. The purpose of this paper is to evaluate the impact of yeast Williopsis saturnus var. saturnus on stability of LAB and probiotic Lactobacillus rhamnosus in fermented milks.

Fermented milks were made from reconstituted whole milk with different milk solids contents. The milk was fermented with L. rhamnosus DR20 with and without yoghurt cultures. The treatment had yeast added, whereas the control did not. Fermented milks were incubated at different temperatures and samples were taken regularly for microbial count determination.

The effect of the yeast on stability of L. bulgaricus and L. rhamnosus varied with temperatures: no effect at 4 and 40 ^○C, increasing effects from 10 to 30^○C with enhanced lactobacilli survival by 10² to 10⁷‐fold. The yeast enhanced L. bulgaricus and L. rhamnosus stability by approximately 10⁶ to 10⁷‐fold in fermented milks with 5 per cent w/v and 20 per cent w/v milk solids at 30 ^○C.

Use of live yeast has limitations. The yeast must not ferment lactose and galactose, and fermentable sugars cannot be used as sweeteners to avoid yeast growth. Further understanding of the interaction between yeast and LAB may eliminate the need to add viable yeast.

Use of yeast to enhance stability of LAB and probiotics is a novel concept. Addition of selected yeast could be an effective means of enhancing stability of LAB and probiotics in fermented milks to extend shelf‐life and to retain nutritional value.