Survival Rate of Lactic Acid Bacteria and the Change of ${\beta}-Galactosidase$ Activity in Commercial Yogurts Under the Acidic Conditions

산성조건하에서 시판요구르트의 유산균 생존률과 ${\beta}-galactosidase$의 활성도

Four samples of commercially manufactured yogurts (plain, drinking type) were purchased and evaluated their physico-chemical properties, buffering capacity. And the survival rate of lactic acid bacteria and their ${\beta}-galactosidase$ activity under the acidic conditions (in vitro) were investigated. The values of pH, titratable acidity, viscosity and viable cell counts of yogurts were $3.71{\sim}4.08$, $0.990{\sim}1.045%$, $256{\sim}3164\;cps.$ and $10^8{\sim}10^9\;cfu/ml$, respectively. The volume of 1.0 M-HCl required to reduce the pH of yogurt (50 ml) to minus 2 value was $3.58{\sim}4.33\;ml$. When commercial yogurts were incubated at $37^{\circ}C$ for 120 minutes under the acidic conditions (pH 3.5, 2.5, 1.5), the survival rates of lactic acid bacteria in yogurt were $3.5{\times}10^{-2}{\sim}3.6{\times}10^{-1}%$ at pH 2.5, $8.3{\times}10^{-5}{\sim}4.2{\times}10^{-3}%$ at pH 1.5, respectively, but there was no significant difference at pH 3.5. The remaining activities of ${\beta}-galactosidase$ were $9.4{\sim}36.2%$ at pH 2.5, $4.2{\sim}19.0%$ at pH 1.5, respectively. These results suggested that a significant number of lactic acid bacteria in yogurt might be destroyed in the hostile environment of the stomach, but ${\beta}-galactosidase$ activity from yogurt might be somewhat maintained probably due to the protecting effect by its cell wall and membrane.

국내에서 시판되는 요구르트(plain)의 이화학적 특성 및 산성조건하에서의 유산균의 생존률과 ${\beta}-galactosidase$의 활성도를 측정하였다. pH는 $3.71{\sim}4.08$범위, 적정산도는 $0.990{\sim}1.045%$, 점도는 $256{\sim}3,164\;cps$ 범위였으며, 유산균수는 $10^{8-9}\;cfu/ml$로 규정보다 높았다. 완충능은 요구르트(50 ml)의 고유 pH값에서 -2의 pH값까지 적정하는 데 소비된 1.0 M-HCl의 량으로 $3.58{\sim}4.33\;ml$였다. 산성조건하에서 유산균의 생존율은 pH 3.5에서는 2시간 동안 거의 변화가 없었으며, pH 2.5, 1.5에서는 각각 $3.5{\times}10^{-2}{\sim}3.6{\times}10^{-1}%,\;8.3{\times}10^{-5}{\sim}4.2{\times}10^{-3}%$ 범위였다. ${\beta}-galactosidase$활성은 120분 후에 pH 3.5에서는 큰 변화가 없었으며, pH 2.5, 1.5에서 ${\beta}-galactosidase$의 잔존활성은 각각 $9.4{\sim}36.2%.\;4.2{\sim}19.0%$ 범위로 나타났다. 이상의 결과로 요구르트를 섭취하였을 때 유산균은 위산에 노출되어 극히 그 일부만이 장내에 도달할 수 있을 것이라고 판단되며, ${\beta}-galactosidase$는 유산균의 세포벽이나 세포막 및 요구르트에 포함된 무지고형분의 보호를 받아 그 활성을 어느정도 유지할 수 있으리라 사료된다.