Inhibitory effect of cocoa powder on the growth of a variety of bacteria in different media.

The inhibitory effect of cocoa powder on 102 organisms belonging to 13 genera was determined. All organisms tested were inhibited by 5% cocoa. Shigella, Staphylococcus, Micrococcus, and Bacillus were the most sensitive. The degree of inhibition depended on the organism, temperature of incubation, and the medium in which the cocoa powder was suspended. Of six media tested, lactose broth and nutrient broth were the most inhibitory, while non-fat dry milk was the least inhibitory. Supplementing NB with tryptone or casein reduced the toxicity of cocoa.