The use of antimicrobials in formulations of ready-to-eat meat and poultry products has been identified as a major strategy to control Listeria monocytogenes . The USDA-FSIS recommends no more than 2-logs of Listeria outgrowth over the stated shelf life if antimicrobials are used as a control measure for a product with post-lethality environmental exposure. This study was designed to understand the efficacy of a clean label antimicrobial against the growth of L. monocytogenes as affected by the product attributes. A response surface method-central composite design was used to investigate the effects of product pH, moisture, salt content, and a commercial “clean-label” antimicrobial on the growth of L. monocytogenes in a model turkey deli meat formulation. Thirty treatment combinations of pH (6.3, 6.5, and 6.7), moisture (72, 75, and 78%), salt (1.0, 1.5, and 2.0%), and antimicrobial (0.75, 1.375, and 2.0%) with six replicated center points and eight design star points were evaluated. Treatments were surface inoculated with a 3 log 10 CFU/g target of a five-strain L. monocytogenes cocktail, vacuum packaged, and stored at 5°C for up to 16 weeks. Populations of L. monocytogenes were enumerated from triplicate samples every week until the stationary growth phase was reached. The enumeration data was fitted to a Baranyi and Roberts growth curve to calculate the lag time and maximum growth rate for each treatment. Linear least-squares regression of the lag-time and growth-rate against the full quadratic, including the second order interaction terms, design matrix was performed. Both lag time and maximum growth rate were significantly affected ( p <0.01) by the antimicrobial concentration and product pH. Product moisture and salt content affected ( p <0.05) lag phase and maximum growth rate, respectively. The availability of a validated growth model assists meat scientists and processors with faster product development and commercialization.

The 2021 FSIS Stabilization Guidelines for Meat and Poultry Products (Appendix B) Option 1.2 limits Phase 1 cooling from 48.8 to 26.7 degrees C in uncured meats to 1 h. However, this time restriction is impractical to achieve in large-diameter whole-muscle products. The objective of this study was to compare the inhibitory effect of commercial dry vinegars (DVs) and cultured sugar-vinegar blends (CSVs) on Clostridium perfringens and Bacillus cereus in uncured beef and poultry products during extended cooling. Treatments (beef: 72-73% moisture, pH 6.2-6.3, 0.85-0.95% NaCl; turkey: 76-77% moisture, pH 6.5-6.7, 1.3-1.6% NaCl) included Controls without antimicrobials, and four DV and four CSV, each tested at 0.75 and 1.25%. Batches were inoculated with 2.5-log C. perfringens or B. cereus spores, vacuum-packaged, and cooked to 73 degrees C. Packages were cooled from 48.8 to 27 degrees C (Phase 1) in 3, 4, or 5 h; Phase 2 (27-12.8 degrees C) and Phase 3 (12.8-4 degrees C) were standardized for 5-h cooling each. Pathogens were enumerated on selective agar in triplicate samples assayed at precook, postcook, and at the end of Phase 1, 2, and 3 cooling. Experiments were conducted twice. B. cereus did not grow (4.5 log) in Control treatments when Phase 1 cooling was extended to >= 3 h. All 1.25% DV ingredients limited C. perfringens growth to <= 1-log when Phase 1 cooling was extended to 3 h but supported a >1-log increase when Phase 1 cooling was extended to 5 h. All 1.25% CSV inhibited growth under 3-h Phase 1 cooling; 1.25% CSV-A and >= 0.75% CSV-D inhibited growth in turkey during 5-h Phase 1 cooling, but inhibition with 1.25% CSV-C was inconsistent in beef. This study revealed that formulating uncured meats with 1.25% DV or certain CSV can extend Phase 1 cooling to 3 h. Although all ingredients inhibited growth when used at 0.75% or greater compared to a control, greater variability of inhibition was observed among CSV than for DV.

Formulating ready-to-eat (RTE) products with growth inhibitors minimizes the risk of listeriosis. In part I, RTE egg products formulated with 6.25 ppm nisin were evaluated to control Listeria monocytogenes. Individual experimental units were surface inoculated with 2.5-log CFU/g of L. monocytogenes, packaged in pouches with a headspace gas of 20:80 CO₂:NO₂, and stored at 4.4°C for 8 weeks. Formulations with finished product pH of 6.29 ± 0.07 limited growth to 0.05) from the control without nisin at pH 7.34 ± 0.13, all supported 4-log growth by 4 weeks. In part II, a nisin bioassay test was performed to evaluate the stability of nisin in eggs as affected by the product pH (6.00 ± 0.03, 7.00 ± 0.00, 7.50 ± 0.03, and 8.00 ± 0.02) and cooking to an internal temperature of 73.9 or 85°C for 90 s. The nisin activity loss increased as the product pH or the cooking temperature increased (p < 0.05). Part III evaluated the effectiveness of 6.25 ppm nisin in combination with either an acetate-based antimicrobial used at 1.0% (w/w) in egg formulation (A1.0), propionate at 0.3% (P0.3), acetate-diacetate at 1.0% (AD1.0), acetate-diacetate at 0.6% (AD0.6), and lactate at 2.0% (L2.0) as a positive control. These formulations had a finished product pH, moisture, and salt contents of 5.97 ± 0.21, 72.4 ± 0.9%, and 0.67 ± 0.05%, respectively. L. monocytogenes did not grow in formulations A1.0 and AD1.0, whereas L2.0 and P0.3 supported 2-log growth by weeks 6 and 15, respectively and AD0.6 supported 0.05) in the CO₂ and O₂ headspace gas composition, generally no detection or growth of background microbes, and no changes (p > 0.05) in the pH of the formulations during storage, all assuring absence of uncontrolled interferences for the growth of L. monocytogenes.

Bacillus weihenstephanensis can grow at refrigeration temperature and cause food poisoning. It has been isolated from liquid whole egg products. The moderate heat used for pasteurization of liquid egg products is ineffective for killing spore-forming bacteria including Bacillus. Available predictive models and a pretrial study in broth suggested the potential for growth of Bacillus spp. under the tested conditions. Hence, hurdles such as storage of product below 4°C or use of preservatives would be needed to ensure the food safety of pasteurized egg products. This study evaluated the growth inhibition of B. weihenstephanensis in pasteurized liquid whole egg product formulated with 6.25 ppm nisin during storage at refrigerated and abuse refrigerated temperatures for a total 13 weeks, in three replicate trials. At day 0, the product had a pH of 7.52±0.29, while background microflora such as aerobic plate counts, presumptive B. cereus, and yeast and molds were <10 CFU/g. Product inoculated with target 2.5 log10 CFU/g of B. weihenstephanensis, stored at 4°C for 4 weeks and subsequently at 7 or 10°C for 9 weeks exhibited no growth in all three replicate trials. Average counts reduced (p<0.05) by at least one-log10 in six weeks in all samples stored at either 7 or 10°C. Similarly, growth of total plate counts, presumptive Bacillus spp., yeast and mold counts was not observed in uninoculated controls stored at 4°C for 4 weeks and subsequently at 7 or 10°C for 9 weeks. Visual and odor evaluation performed at each sampling time point showed no abnormalities. This study assessed the efficacy of maximum allowed level of nisin for use in pasteurized liquid whole eggs and validated the inhibition of B. weihenstephanensis in the product for an extended shelf life of up to 13 weeks.