Effect of Enumeration Method on Bifidobacterium Cell Counts in Commercial Powder Products

In this study, the effects of enumeration methods on viable bifidobacterial counts in powder products were examined to determine the most appropriate enumeration conditions. The bifidobacterial counts of nine commercial powder products containing Bifidobacterium species were determined by a pour plate method using different diluents including Mitsuoka's buffer and Ringer's solution. Mitsuoka's buffer gave significantly higher bifidobacterial counts than Ringer's solution when used as diluent for eight of nine commercial powder products containing various Bifidobacterium species. The counts obtained with Ringer's solution were on average 51.6% of those obtained using Mitsuoka's buffer. Addition of Tween 80 or phosphate buffer to Ringer's solution increased the bifidobacterial counts. Also, the diluent had a significantly greater impact in the suspension step than in the subsequent dilution step. In conclusion, the diluent has great effect on the enumeration of bifidobacteria when using the plate count method. Also, the composition of diluents influences bifidobacterial counts.