Ready-to-eat egg products formulated with nisin and organic acids to control Listeria monocytogenes

Authors: SHRESTHA, SUBASH - Cargill, Incorporated; ERDMANN, JERRY - International Flavors And Fragrances Inc; RIEMANN, MICHELLE - Cargill, Incorporated; KROEGERA, KEVIN - Cargill, Incorporated; Juneja, Vijay; BROWN, TED - Cargill, Incorporated

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2023
Publication Date: 3/28/2023
Citation: Shrestha, S., Erdmann, J.J., Riemann, M., Kroegera, K., Juneja, V.K., Brown, T. 2023. Ready-to-eat egg products formulated with nisin and organic acids to control Listeria monocytogenes. Journal of Food Protection. 86:100081. https://doi.org/10.1016/j.jfp.2023.100081.
DOI: https://doi.org/10.1016/j.jfp.2023.100081

Interpretive Summary: Ready-to-eat egg products have been linked to multistate Listeria monocytogenes food poisoning outbreaks. These products are distributed and stored under refrigerated conditions which potentially increase the food safety risk including the growth of the pathogen during shelf life. We investigated the effectiveness of nisin alone or in combination with organic acids in egg formulations to inhibit the growth of L. monocytogenes. Our results suggest that a combination of nisin and organic acids in eggs at pH 6.0 controlled Listeria for an extended period during refrigerated distribution and storage. Egg processors can use the information to guard against L. monocytogenes in ready-to-eat egg products.

Technical Abstract: Formulating ready-to-eat products with growth inhibitors is a demonstrated strategy to significantly minimize the risk of listeriosis. The USDA lists nisin as “safe and suitable” for use in egg products at =6.25 ppm. In phase I, ready-to-eat egg products formulated with 6.25 ppm nisin were evaluated to control Listeria monocytogenes. Individual sample units were surface inoculated with 2.5-log CFU/g of L. monocytogenes, packaged in a pouch 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 <2-log for four weeks, but products at pH values 7.42±0.12 and 7.84±0.11 were not different (p>0.05) from the control without nisin at pH 7.34±0.13, all supported 4-log growth by four weeks. In phase 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 seconds. The loss in nisin activity increased as either the product pH or the cooking temperature increased (p<0.05). Phase 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 blend at 1.0% (AD1.0), acetate-diacetate blend at 0.6% (AD0.6), and lactate at 2.0% (L2.0) as a positive control. These formulations with finished product pH of 5.97±0.21 were inoculated, packaged, and stored at 4.4°C for 20 weeks. Listeria 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, and AD0.6 supported <1-log growth over 20 weeks. Evaluation of uninoculated control units suggested no changes (p>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 in phase I and III.