Determination of 5-Log Reduction Times for Escherichia coli O157:H7, Salmonella enterica, or Listeria monocytogenes in Acidified Foods with pH 3.5 or 3.8

Acidified foods, such as dressings and mayonnaise, must be processed to ensure the destruction of vegetative bacterial pathogens like Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes. While heat treatment is a standard method for achieving this, it can negatively impact the sensory quality of certain products. Consequently, manufacturers often rely on holding times at specific pH levels to ensure safety. This study aimed to define the necessary holding times at 10°C to achieve a 5-log reduction of these pathogens in brines containing various combinations of acetic and benzoic acids at pH 3.5 and 3.8.

The researchers used a cocktail of five strains for each of the three pathogens, pre-adapted to acid stress to simulate a worst-case scenario. Experiments were conducted in pasteurized cucumber juice, which provides a nutrient-rich environment that can support pathogen survival. The team tested 15 different combinations of acetic acid (1.5% to 2.5%) and benzoic acid (0% to 0.1%) at pH 3.5 and 3.8. Survival was monitored over time, and a linear mixed effects model was used to calculate the time required for a 5-log reduction for each condition.

The study confirmed that E. coli O157:H7 is significantly more acid-resistant than S. enterica and L. monocytogenes. The results demonstrated that the inclusion of 0.1% benzoic acid substantially accelerates the lethality of the brine. For instance, at pH 3.8, the addition of benzoic acid reduced the time required for a 5-log reduction by more than sevenfold in 2.5% acetic acid solutions. Under the tested conditions, a 5-log reduction could be achieved in 4 days or less using 2.5% acetic acid at pH 3.5, or 2.5% acetic acid with 0.1% benzoic acid at pH 3.8. These findings provide critical data for food manufacturers to support process filings under the Food Safety Modernization Act (FSMA).