No abstract

The behavior of Listeria monocytogenes was evaluated during storage of a queso blanco type of cheese produced with acidulants (citric, malic, or acetic acids) and a commercial lactic acid bacterium fermentation product, ALTA™2341 (ALTA). The cheese was prepared by direct acidification (final pH 5.2), with and without 0.6% ALTA, inoculated with 106 CFU/g of L. monocytogenes, and stored at 4 or 20°C for 42 and 7 days, respectively. Levels of L. monocytogenes increased in cheese coagulated with citric or malic acids and stored at 4°C, but decreased slightly in cheese coagulated with acetic acid. At 20°C, counts of L. monocytogenes increased in cheeses acidified with citric or malic acid, but counts did not increase appreciably in cheese acidified with acetic acid. When cheese was stored at 4°C, the presence of 0.6% ALTA resulted in lower counts of L. monocytogenes compared with counts in cheese that did not contain ALTA. However, at 20°C populations of L. monocytogenes increased in cheese containing ALTA regardless of acid type. Additional studies compared the effects of acetic acid, alone or in combination with 0.6 or 2.5% ALTA, against low (102 CFU/g) and high (106 CFU/g) inoculum levels. When inoculum levels were low, pathogen counts decreased by > 1.1 log10 CFU/g in all formulations at 4°C. After 7 days at 20°C, pathogen counts increased in the queso blanco type of cheese prepared with acetic acid alone. In contrast, in the presence of 0.6 or 2.5% ALTA, 7-day counts were less than the initial inoculum. With high inoculum levels at 4°C, counts of L. monocytogenes were less than the initial inoculum in the acetic acid-coagulated queso blanco type of cheese with or without ALTA. At 20°C, counts increased in the queso blanco type of cheese prepared with 0.6% ALTA, but decreased appreciably in cheese prepared with 2.5% ALTA. These results demonstrate that acetic acid is significantly more effective than malic or citric acids for controlling L. monocytogenes in queso blanco, and that inclusion of ALTA can provide added protection against the pathogen.

The antilisterial activity of sodium diacetate and a commercial shelf-life extender (ALTA™ 2341) were monitored at 25°C in slurries prepared with turkey breast meat. In slurries prepared without either ingredient, populations of Listeria monocytogenes increased about 5-log10 units in 7 d. The addition of 0.3% diacetate extended the generation time (7 h) compared to the control (no food additives; 1.7 h), whereas 0.5% inhibited the pathogen somewhat (0.4-log10 unit decrease in 7 d compared to the control). Slurries containing ALTA (0.25, 0.5, or 0.75%) and 0.3% diacetate extended the lag phase of L. monocytogenes to a greater extent than slurries with 0.3% diacetate alone. In contrast, 0.5% diacetate in combination with all three levels of ALTA tested was listericidal (ca. 2-log10 unit decrease after 7 d compared to the control). These data confirm the efficacy of diacetate for inhibiting L. monocytogenes in turkey meat and indicate that multiple barriers such as diacetate with ALTA may further lessen the likelihood of food-related listeriosis.