Enumeration Of Bifidobacterium Spp., Lactobacillus Acidophilus and Starter Cultures from Commercial Probiotic Yogurts and Freeze-Dried Yogurt Starter Mixes

Abstract

Probiotic yogurt is a popular functional food to deliver of probiotic cells for the health-enhancing effects worldwide. The viability of probiotics in yogurt before consumption is the most important factor to providing desired effects, however, probiotic microorganisms have occasionally inadequate viability in marketable food products. In this current study, Bifidobacterium spp., L. acidophilus and yoghurt starter bacteria enumerations were made in commercial probiotic yoghurt and freeze-dried yogurt mixes. RCA 5.3 and MRS 5.2 media were used for L. delbrueckii subsp. bulgaricus counting, ST Agar and M17 Agar were used for Stretococcus thermophilus counts. While using MRS-Bile Agar and RCA-Clindamycin Agar for L. acidophilus enumeration, Bifidobacterium spp. counts were performed using MRS-NNLP medium. 5 out of yoghurt samples (A, C, D, and E) did not reveal satisfactory recovery (< 5 log CFU/g) for L. delbrueckii subsp. bulgaricus colonies on MRS 5.2 Agar while L. delbrueckii subsp. bulgaricus colony counts on RCA 5.3 Agar below 5 log CFU/g for same tested 4 samples (A, C, D, and E). The recovery rates over 9 log CFU/g were obtained in the enumerations made for all yogurt samples on both ST and M17 media. The problem of insufficient recovery rates that occurred for L. delbrueckii subsp. bulgaricus in some yogurt samples was not valid for S. thermophilus. This work indicated that high amounts of L. acidophilus were detected on both media in both of the two yoghurt samples declared as L. acidophilus on the label (F and G). On the other hand, bifidobacteria was determined above 5 log CFU/g in only 1 yoghurt sample (B) out of 7 probiotic yoghurts claimed to be Bifidobacterium spp. This study reveals relevant information on probiotic and starter counts of commercial probiotic yogurts in Turkey and discusses in detail the possible reasons for the results obtained.