The effect of acid shock on the heat resistance of Listeria monocytogenes

• Published in: Letters in applied microbiology 1992-11, Vol.15 (5), p.197-201
• Main Authors: Farber, J.M., Pagotto, F.
• Format: Article
• Language: English
• Subjects: Action of physical and chemical agents on bacteria; Bacteriology; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Listeria monocytogenes; Microbiology
• ISSN: 0266-8254; 1472-765X
• DOI: 10.1111/j.1472-765X.1992.tb00762.x

The effect of acid shock on the heat resistance of Listeria monocytogenes was investigated. After growth for 24 h at 30°C in tryptic soy broth containing 0.6% yeast extract, cell culture suspensions of L. monocytogenes were acidified with HCl or acetic acid over various time periods before being heated in whole milk to a temperature of 58°C. When cells were acid‐shocked immediately with HCl for 1, 2 or 4 h, those acid‐shocked for 1 h demonstrated the largest increase in thermotolerance as compared to control cells, when heated at 58°C in whole milk. In fact, cells acid‐shocked for longer than 1 h with HCl demonstrated in some instances a decreased recovery as compared to control cells. Other types of acid‐shock treatments included lowering the pH gradually either over a 4 h or a 24 h period. However, regardless of the type of acid‐shock treatment, cells acid‐shocked with HCl (but not acetic acid) prior to heating had significantly greater heat resistance as compared to control (non‐acid‐shocked) cells. It appears that acidification with HCl prior to final heating can enhance the heat resistance of L. monocytogenes.