Sour cream can be carrier of probiotic cultures.

In recent years, because of their reported health benefits, the dairy industry has begun incorporating probiotic cultures into many products such as yogurt and cheese. However, in order to be beneficial, the cultures have to remain live and active at the time of consumption.

Researchers in North Carolina wanted to determine the survival and growth of probiotic bifidobacteria and Lactobacillus reuteri in commercially available sour cream. They obtained fresh sour cream samples from a local market and inoculated them with one of these probiotic strains: L. reuteri (MM 2-3 and MM 7) and B. longum (ATCC 5708 and NCFB 2254). The scientists wanted to obtain a final inoculum level of [10.sup.7] cfu per ml. Indeed, they found that it is feasible to use sour cream as a probiotic carrier.

In their work, the researchers mixed the sour cream samples thoroughly and refrigerated them at 4 C for two weeks. The scientists analyzed the samples for a viable bacterial count using a modified BIM 25 agar to enumerate bifidobacteria and an MRS agar supplemented with 50 mg per ml of vancomycin to enumerate Lactobacillus.

Although the bacterial counts decreased, the products contained an average 5.0 x [10.sup.5] cfu per ml of viable probiotics after 15 days of storage. There were significant differences among the tested strains during the time of storage. L. reuteri MM 2-3 showed a slight decline of viability, although it was not significant over the storage period. Each B. longum strain had a two-log reduction, while L. reuteri MM 7 had a one-log reduction over the storage period.

Probably the best-studied probiotics are the lactic acid bacteria, particularly Lactobacillus sp. and Bifidobacterium sp. However, other organisms used as probiotics in humans include Escherichia coli, Streptococcus sp., Enterococcus sp., Bacteroides sp., Bacillus sp., Propionibacterium sp. and various fungi. Some probiotic preparations may contain mixtures of more than one bacterial strain.

Further information. Chung Seo, Food Science and Nutrition Program, Department of Human Environment and Family Sciences, North Carolina A&T State University, 171-B Carver Hall, Greensboro, NC 27411; phone: [phone]; email: [e-mail].