Probiotics are live microbial strains that, when consumed in adequate doses (106e107 cfu mL1), beneficially affect the host animal, by improving its intestinal microbial balance. However, these organisms grow slowly in milk and often show loss of viability during cold storage. Also, the viability of probiotics is affected by the presence of lactic acid. Acid production by Lactobacillus delbrueckii subsp. bulgaricus is the major cause for viability reduction of probiotics in fermented milk