Populations of Lactobacillus acidophilus, Bifidobacterium spp., and Lactobacillus casei in Commercial Fermented Milk Products

Abstract

The populations of Lactobacillus acidophilus, Bifidobacterium spp. and Lactobacillus casei were examined in 26 commercial fermented milk products represented by 14 companies. Six products contained L. acidophilus only, 12 products contained L. acidophilus and bifidobacteria, 6 products claimed L. acidophilus, bifidobacteria, and L. casei, and 2 products contained L. casei only as the probiotic organism. The initial bacterial count was enumerated immediately after purchase and the final count at the expiry date. L. acidophilus was enumerated on MRS-salicin agar and MRS-sorbitol agar, bifidobacteria on MRS-NNLP (nalidixic acid, neomycin sulfate, lithium chloride, paromomycin sulfate) agar, and L. casei on LC agar. The counts of L. acidophilus decreased below 106 cfu/g in all the 6 products that contained L. acidophilus only. The counts of L. acidophilus decreased below 106 cfu/g in 75 % of the products that contained L. acidophilus and Bifidobacterium spp. at the expiry date. The population of bifidobacteria dropped below 106 cfu/g in 94 % of the products that claimed L. acidophilus, Bifidobacterium spp. or L. acidophilus, Bifidobacterium spp. and L. casei. Similarly, 50% of the products that contained L. acidophilus, Bifidobacterium spp. and L. casei showed L. casei count of < 106 cfu/g. The counts of L. casei in one of the two products that contained L. casei only dropped below 102 at the expiry date. The pH in all the products decreased during storage.