Influence of water activity on the fermentation of yogurt made with extracellular polysaccharide-producing or non-producing starters

Ropy and non-ropy strains of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus were studied with respect to their resistance to reduction of water activity in milk used to produce yogurt. Glycerol reduced the a w of the milk considerably, but it was less inhibitory to acid production than sucrose. The ropy strains did not show any advantage over nonropy ones when they were used to produce yogurt in milk with reduced a w; their performance was similar to non-producer strains in terms of lactic acid production.