熱震處理影響Streptococcus thermophilus 之脂肪酸組成及其在後續致死環境壓力下之存活

Abstract

Streptococcus thermophilus為食品工業中極具經濟價值的乳酸菌，常做為發酵乳及起司之菌酛。本研究乃在探討熱震處理 (50℃，30分鐘) 對S. thermophilus BCRC 14085脂肪酸組成的影響，以及在脫脂乳中產酸及生長情形的影響，並觀察菌體經熱震處理後暴露於氧化壓力 (10 mM過氧化氫)、高鹽 (6%氯化鈉)、5 % Clidox-SR (含氯消毒劑)、0.2 % QuatricideR (四級銨消毒劑)、冷藏儲存 (5℃) 及乳酸菌飲料中之存活情形。 結果顯示，經熱震處理後S. thermophilus所含之棕櫚酸 (palmitic acid)及硬脂酸 (stearic acid) 顯著增加，次亞麻油酸 (linolenic acid) 含量顯著降低，熱震處理組菌體飽和脂肪酸與不飽和脂肪酸之比值 (SFA/USFA) 亦顯著增加。接著觀察熱震處理對S. thermophilus於脫脂乳中發酵能力的影響，結果顯示熱震處理後的菌體與控制組菌體之產酸及生長情形皆無顯著差異，顯示熱震處理並不影響菌體的發酵功能。且熱震處理顯著提高了菌體在氧化壓力 (10 mM H2O2)、5 % Clidox-SR、0.2 % QuatricideR下之存活率。然而經過熱震處理後增加了菌體對高鹽 (6%) 環境的敏感性，但在冷藏 (5℃) 及乳酸菌飲料中兩組之間存活率並無顯著差異。

Streptococcus thermophilus is one of the most important lactic acid bacteria widely used in yogurt and cheese production. In the present study, S. thermophilus BCRC 14085 was subjected to heat shock treatment (50℃, 30minutes). The effect of heat shock on the fatty acid composition and the viability of S. thermophilus BCRC 14085 during the fermentation of skim milk (37℃) were investigated. Survival of heat-shocked S. thermophilus during subsequent exposure to various stress conditions, including oxidative (10 mM hydrogen peroxide, H2O2), salt (6 % sodium chloride), 5 % Clidox-SR (chlorine-containing disinfectant), 0.2 % QuatricideR (quaternary ammonium compound), refrigerated storage (5℃) and lactic fermented drink were also examined. It was found that heat shock significantly (p < 0.05) reduced the proportion of linolenic acid (18 : 3), while increased the proportion of palmitic acid (16 : 0), stearic acid (18 : 0) and the ratio of saturated fatty acids to unsaturated fatty acids in cells of S. thermophilus. The growth behavior and acid productivity of the heat-shocked and the control S. thermophilus cells during the skim milk fermentation period showed no significant difference (p > 0.05). Besides, heat shock enhanced the survival of S. thermophilus exposure to H2O2 and sanitizers (Clidox-SR and QuatricideR). While, heat shock increased sensitivity of S. thermophilus subjected to high salt treatment. On the other hand, viability of heat shocked and control cells showed no significant difference (p > 0.05) during the refrigerated storage of lactic fermented drink.