| Summary: | 碩士 === 國立臺灣大學 === 食品科技研究所 === 102 === 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.
|
|---|
