Lactobacillus acidophilus NCFM Survival in Acidified Yogurts

Abstract

Lactobacillus acidophilus NCFM is a probiotic culture widely added to dairy products and dietary supplements. The bacterium has been linked with immune modulation, cold prevention in humans, and relief of gut pain via a morphine like mechanism in animals. Industrially, the target for delivery of viable cells in a 6 oz. serving of yogurt at the end of a 52 day shelf-life is 2 x 106 CFU/g. Survival studies with an industrial yogurt formulation showed that counts of NCFM fell to less than 102 CFU/g at the end of shelf-life. The objective of this study was to investigate the reasons for the dramatic loss of viability during shelf-life, and define a solution that could maintain viability throughout shelf-life. Levels of NCFM were followed in fermented yogurts at pH 4.1, 4.7 and 5.0. Results showed that with inoculation levels of 108 CFU/ml, NCFM added at the outset of fermentation maintained survival in yogurts acidified at pH 4.7 and 5.0. NCFM showed poor survival in yogurts acidified to pH 4.1, exhibiting a 3 log loss after 48 days. The possible effects of cell injury in lyophilized Lb. acidophilus NCFM cells were also investigated. Cells subjected to a 60 minute resuscitation period in MRS media, prior to addition to acidified yogurt base at pH 4.1, showed only a ~1.5 log loss after 42 days. Survival of NCFM in yogurt was compromised at acidic conditions below pH 4.7 and a recovery period of the lyophilized cells can greatly improve survival.