본 연구는 합성기질인 $X-{alpha}-Gal$를 이용하여 발효유 및 유제품내의 Bifidobacteria 생균수를 측정할 목적으로 하였다. 젖산균과 Bifidobacteria의 ${alpha}-galactosidase$ specific activity를 측정한 결과 Bifidobacteria 균주에서는 높은 ${alpha}-galactosidase$ activity를 가지고 있었으며, 그 중 Bif. longum KCTC 3215의 specific activity는 8.57 unit/mg protein으로 가장 높게 나타났다. Lactobacillus, Streptococcus, Pediococcus와 Leuconostoc 균주에서는 활성이 미약하거나 없었다. 합성기질인 $X-{alpha}-Gal$을 MRS agar 배지에 $100{;}{mu}M$ 첨가한 결과 Bifidobacteria는 blue colony로, Lac. bulgaricus, Lac. casei와 Leu. mescenteroides 균주는 light blue colony로, 그 외 젖산균에서는 white colony로 나타났다.
This method using the synthesis substrate of $5-bromo-4-chloro-3-indolyl-{alpha}-galactoside;(X-{alpha}-Gal)$ was examined for the differential enumeration of Bifidobacteria and lactic acid-producing bacteria. Bifidobacteria possess a high level of ${alpha}-galactosidase$ activity. Bifidobacterium longum KCTC 3215 exhibited the highest ${alpha}-galactosidase$ specific activity (8.57 units/mg protein). Determination of ${alpha}-galactosidase$ activity using the PNPG procedure showed that Lactobacillus, Streptococcus, Pediococcus, and Leuconostoc strain had lower ${alpha}-galactosidase$ activity as compared to Bifidobacteria. The $X-{alpha}-Gal$ based medium is useful to identify Bifidobacteria among lactic acid-producing bacteria since the enzyme action of ${alpha}-galactosidase$ spills $X-{alpha}-Gal$ substrate and releases indol which impacts a blue color to Bifidobacterial colonies on agar plates. All strains of Bifidobacteria appeared as blue colonies on MRS agar medium supplemented with $100;{mu}M;X-{alpha}-Gal$ while colonies of other lactic acid-producing bacteria appeared white or light blue.
