Selective determination of Bifidobacterium, Lactobacillus acidophilus and Lactobacillus casei from probiotic yoghurts

Abstract

During the experiments I examined different probiotic yoghurt products. The aim of the study was to determine separately the number (titer) of the natural yoghurt flora and the probiotic microflora, found in the products, faster than the usual methods.

We used the following products and microbes during the experiments: Unflavoured yoghurt (Danone): Streptococcus thermophylus, Lactobacillus delbruecki subsp. bulgaricus ”Activia” yoghurt (Danone): Streptococcus thermophylus, Lactobacillus delbruecki subsp. bulgaricus, ’Bifidus Acti-regularis’ ”Actimel”: Streptococcus thermophylus, Lactobacillus delbruecki subsp. bulgaricus, ’L. casei defensis’ ”Bakony joghurt plusz”: Streptococcus thermophylus, Lactobacillus delbruecki subsp. bulgaricus, Bifidobakteria, Lactobacillus acidophylus We used the fact that the sugar fermentation ability and the pH range of multiplication of the normal yoghurt flora and the certain probiotics are different.

I determined that the normal yoghurt microflora could grow only in the MRS broth with lactose content at pH 6.5. In the other pH 4,5 or 6,5 broth which contained maltose or ribose as sugar source only the certain probiotics can grow. Using this fact these microbes can be differentiated from the normal yoghurt microflora, and with certain limits these microbes can be separated from each other also. We determined with storage examinations that “Danone Activia” yoghurt and “Actimel” contain the required amount of probiotics till the end of the shelf life. In the “Bakony joghurt plusz” product the number of bifidobacteria is low at the beginning of shelf life also; the cause is the lower pH value of the product.