Viability of probiotic bacteria in fermented frozen dairy desserts

Yogurt bacteria (Streptococcus thermophilus and Lactobacillus delbruekii ssp. bulgaricus) and probiotic bacteria (Lactobacillus acidophilus and Bifidobacterium spp.), 41 strains in all, were screened for ability to survive under frozen conditions, in presence of sugar (8 and 16%) and under acidic conditions. Three batches of yogurt prepared using three different strains each of S. thermophilus, L. delbrueckii ssp. bulgaricus, L. acidophilus and Bifidobacterium spp. were mixed with a base mix and frozen. In a separate experiment, three batches of yogurt were made with yogurt bacteria only and probiotic bacteria were added just before freezing. The viability of yogurt and probiotic organisms in the frozen desserts was monitored for 12 weeks. Further, two 1000 L batches of fermented dairy desserts were made using selected strains of yogurt and probiotic bacteria and the viability of both organisms was monitored for 12 weeks. Most of the organisms survived freezing, acidic conditions and the presence of high levels of sugar.