Usefulness of epifluorescence for quantitative analysis of lactobacilli in probiotic feed

Enumeration of total, active or viable probiotic micro-organisms from liquid or solid commercial feedstuffs was studied during processing and storage.

After sample preparation, an epifluorescence microscopy technique and a plating method were investigated comparatively. It was shown that (i) on the day of manufacture, active or viable bacteria were in equivalent amounts and that viable numbers then decreased, depending on the different processing and storage factors enhancing ABNC production, (ii) the amount of total and active lactobacilli remained close and quite stable for months at a high level (>10(8) active fluorescent units).

Processing and storage promoted ABNC cells in the products tested. Consequently, both techniques should be used to evaluate the viable-dead-active status of bacteria for which functional properties are claimed.

Enumeration of the whole probiotic bacterial population should be take into account for guidelines and labelling since non-viable bacteria could have a probiotic effect.