Effect of Heat Shock on the Survival of Streptococcus thermophilus Under Subsequent Lethal Stresses
| Autor: | Ying-Hsuan Lee, 李盈萱 |
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| Rok vydání: | 2013 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 Streptococcus thermophilus is a thermophilic lactic acid bacteria which was commonly used as the starter organism of yoghurt and some cheese. In the present study, S. thermophilus BCRC 14085 was first subjected to sub-lethal heat treatments (heat shock). Its survival in subsequent lethal stress environments such as high temperature, freezing storage, acidic (pH 2.5) environment, high osmotic pressure, ethanol, organic acid, drying process (spray drying and freeze drying) and simulated gastrointestinal juice were investigated. Results revealed that heat shock treatments increased the thermal tolerance of S. thermophilus BCRC14085 at 58℃. Heating at 50℃ for 30 min, among the various heat shock treatments examined, was found to enhance the thermal tolerance most profoundly. Besides, heat shock enhanced the survival of test organism exposd to high osmotic pressure (aw ca. 0.75), acid (pH 2.5), 25% ethanol, frozen storage (-20℃) and organic acidic (0.75 M lactate, acetate and citrate, pH 3.5). Furthermore, heat shock was also noted to increase significantly (p < 0.05) the survival of S. thermophilus subjected to spray drying process or exposed to simulated gastrointestinal juice (pH 2.5-3.0 and 2% bile salt). |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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