Acidification of Model Cheese Brines To Control Listeria monocytogenes

Abstract

ABSTRACT Cheese brines are often used for prolonged periods, with adjustments made only to pH and salt content. Pathogens, including Salmonella enterica Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes, have been shown to survive long periods in model and commercial brines under common brining conditions. The objective of this study was to determine the survival of L. monocytogenes in model cheese brines, with and without whey added at 2%, when acidified to a pH of 2 using food-grade acids. Survival in untreated brines over a 6-month period was also assessed. Cultures of L. monocytogenes were propagated to induce salt and acid tolerance prior to inoculation at ∼6 log CFU/mL into model brines (pH 5.2, 20% NaCl). Following a week-long adaption period at 12°C, inoculated brines were acidified to pH 2.0 within 15 min using either hydrochloric, acetic, citric, or lactic acid, held at that pH for up to 24 h, and neutralized prior to enumeration and enrichment. Overall, each acid treatment was capable of achieving ≥5-log reductions in L. monocytogenes counts within 135 min at pH 2. Hydrochloric acid required the lowest volume to achieve treatment pH and was the most effective treatment in the absence of whey. However, it was the least effective in the presence of whey. Acetic acid produced rapid inactivation in both brines but required impractical volumes of acid to reach the treatment pH. Citric acid was similarly effective in both brines but was the second least effective in terms of time to achieve a ≥5-log reduction. Although only slight and insignificant differences were observed, lactic acid appears to be the more practical and promising approach for the inactivation of L. monocytogenes in cheese brines by producing the most rapid inactivation in the presence and absence of whey. Acidification as a preventive control for L. monocytogenes could increase adoption of brine treatments by small-scale cheese producers, thereby reducing food safety risks.