Chapter 10 Media for the detection and enumeration of bifidobacteria in food products

Abstract

Bifidobacteria are commonly used for the production of fermented milks in combination with other lactic acid bacteria. It is important that bifidobacteria claimed to be present in a dairy product should survive in relatively high viable cell numbers (>10 6 per g) until consumption. Hence, the need exists for rapid, reliable methods for enumeration of bifidobacteria, both to routinely determine the initial inoculum and to estimate the time bifidobacteria remain viable. Plate count methods are still preferable for quality control measurements in dairy products. A selective medium is therefore, necessary that promotes the growth of bifidobacteria, but suppresses other bacteria. This chapter reviews media and methods, including summaries of published comparisons between different selective media. Culture media for bifidobacteria may be divided into basal, elective, differential and selective. Non selective media such as RCM (Reinforced Clostridial Medium) and MRS (de Man, Rogosa and Sharpe) agar, are useful for enumeration of bifidobacteria when present as pure cultures in non-fermented milk or in fermented milks made only with bifidobacteria. Many selective or differential isolation media have been described for enumeration of bifidobacteria in the presence of other lactic acid bacteria. There is no standard medium for the detection of bifidobacteria. However, Columbia agar base medium supplemented with lithium chloride and sodium propionate and MRS medium supplemented with neomycin, paromomycin, nalidixic acid and lithium chloride can be recommended for selective enumeration of bifidobacteria in food products.