Effect of Cold-Shock Treatments on the Survival of Streptococcus thermophilus Under Subsequent Lethal Environmental Stresses
Date Issued
2010
Date
2010
Author(s)
Fang, Shiu-Hui
Abstract
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.
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.
Subjects
cold shock conditions
subsequent lethal stresses
Type
thesis
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