冷震處理影響Streptococcus thermophilus在後續一些致死壓力下之存活

Abstract

Streptococcus thermophilus為具耐熱性乳酸菌，常用於酸凝乳及一些起司之發酵上當作菌酛。本研究乃在探討S. thermophilus BCRC 14085於不同冷震條件 (10℃、15℃或20℃下經2或4 h) 處理後，在後續致死壓力環境下如在高溫 (58℃)、酸性 (pH 2.5)、高滲透壓 (75% sorbitol)、乙醇 (20、25%)、有機酸 (0.75 M丙酸、乳酸、醋酸、檸檬酸及酒石酸，pH 3.5)及模擬胃腸液下 (pH 2.0-3.0) 之存活情形。 結果顯示，S. thermophilus所呈現之冷震效應會因冷震條件及測試壓力種類之不同而有所差異。以10℃-2 h、10℃-4 h及15℃-2 h冷震處理可顯著 (p＜0.05) 提高S. thermophilus於-20℃環境下之存活率，但20℃- 4 h冷震處理卻反而提高菌體於-20℃環境下之敏感性。S. thermophilus接受10℃-2 h及10℃-4 h冷震處理後顯著(p＜0.05) 提高其於58℃、酸性 (pH 2.5) 及高滲透壓環境下菌體之耐受性，但以20℃- 2 h 及20℃- 4 h冷震處理者在58℃、酸性 (pH 2.5) 下之忍受性則降低。此外，10℃-2 h冷震處理菌體在25%乙醇環境耐受性比控制組高。惟在0.75 M乳酸或醋酸溶液 (pH 3.5) 中，其情形剛好相反。10℃-2 h冷震組及控制組在0.75 M檸檬酸或酒石酸溶液 (pH 3.5) 中之存活率卻沒有顯著性 (p＞0.05) 差異。10℃-2 h冷震處理提升了S. thermophilus在模擬胃酸中 (pH 2.5、2.8) 之耐受性；但在2%膽鹽溶液中，10℃-2 h冷震菌體及控制組菌體之存活並未有顯著性 (p＞0.05) 之差異。

Streptococcus thermophilus is a thermophilic lactic acid bacteria which is used as the starter organism of yoghurt and some cheese. In the present study, S. thermophilus BCRC14085 was first subjected to different cold shock treatments (10℃, 15℃ or 20℃ for 2 h or 4 h). Their survivals in subsequent lethal stress environments such as high temperature (58℃), acidic pH (2.5), high osmotic pressure (75% sorbitol), ethanol (20, 25%), organic acid (0.75 M propionic acid, lactic acid, acetic acid, citric acid and tartaric acid, pH 3.5), simulated gastrointestinal juice (pH 2.0-3.0) were then examined. It was found that cold shock response of S. thermophilus varied with the conditions of cold shock and types of tested lethal stresses. Cells of S. thermophilus BCRC 14085 subjected to cold shock at 10℃ for 2, 4 h or 15℃ for 2 h showed a significantly enhanced (p＜0.05) survival at -20℃ when compare with the control cells. Whereas 20℃-4 h cold shocked-cells exhibited a reduced survival. Cold shock at 10℃ for 2 or 4 h enhanced while cold shock at 20℃ for 2 or 4 h reduced the tolerance of test organism at 58℃, in acidified MRS broth (pH 2.5) and under high osmotic pressure condition. Furthermore, the 10℃-2 h cold shocked-cells showed a higher tolerance in 25% ethanol and a reduced tolerance after exposure to 0.75 M lactic acid or acetic acid (pH 3.5) compared to the control cells. On the other hand, survivals of the 10℃-2 h cold shocked-cells and control cells in presence of 0.75 M citric acid or tartaric acid (pH 3.5) showed no significant difference (p＞0.05). Additionally, cold shock at 20℃ for 2 h enhanced the tolerance of S. thermophilus in the simulated gastric juice (pH 2.5, 2.8), while did not significantly (p＞0.05) affect ther survival in 2% bile solution.