Exploring the Impact of the Matrix on the Growth of Listeria monocytogenes

Abstract

Listeriosis is a significant foodborne illness mainly resulting from the consumption of food contaminated with Listeria monocytogenes. This study aimed to evaluate how different nutrient compositions of UHT bovine milk, infant formula, and plant-based beverages (almond and coconut) influence the growth of Listeria monocytogenes at 25 °C, thereby providing insight into potential microbial risks associated with both animal- and plant-derived milk products. Nutrient broth was used as a reference control. Beverage samples were inoculated with Listeria monocytogenes at approximately 9 × 10⁷ CFU/mL. The inoculated samples were stored at 25°C and sampled on the 1, 3, 6, 24, 48 and 72 hours of incubation. The findings indicate that Listeria monocytogenes was capable of proliferating in all the samples reaching the highest counts on the 48^th hour of the evaluation. Although that on the 48^th hour of evaluation, coconut beverage had the lowest bacteria counts (7.5±0.98 CFU/mL), no statistically important differences in growth rates between diverse evaluated beverages was noted. At the 72-hour incubation period, infant formula exhibited the highest microbial counts, at a value of 8 logs, whereas the coconut beverage showed the lowest microbial counts at 6 logs. The obtained data indicate that all the assessed beverages could pose a considerable threat for listeriosis, and post-opening guidelines should be thoroughly evaluated.