## 1 Introduction
While fat itself does not serve as a primary growth substrate for \(Lm\), its presence significantly impacts bacterial survival and potential growth dynamics. Notably, lipid components can confer a protective effect against antimicrobial interventions. Furthermore, the overall food matrix, including its lipid content, influences physicochemical properties such as water activity, which, in turn, modulates \(Lm\) growth. Research indicates that the microstructure of fatty foods also plays a role in influencing bacterial growth patterns. Additionally, while \(Lm\) does not directly metabolize lipids, the presence of fats and oils contributes to the overall nutrient milieu, potentially supporting bacterial proliferation. Finally, the fatty acid composition of the surrounding food matrix can influence the composition of the \(Lm\) cell membrane, especially during adaptation to low temperatures. Consequently, although fat is not a direct growth promoter, it creates an environment that can enhance \(Lm\) survival and influence its growth trajectory. Therefore, rigorous handling and processing protocols are crucial for fatty, ready-to-eat food products to mitigate the risk of \(Lm\) contamination [42; 43; 44; 45]. In 2023, the listeriosis notification rate in the EU/EEA stood at 0.66 cases per 100,000 population [1]. This represented a 5.8% increase compared to the 2022 rate (0.63 cases per 100,000 population) and marked the highest incidence rate and cases reported since 2007. Additionally, the overall trend in \(Lm\) infections showed a statistically significant increase over the 2019-2023 period [1]. In Greece, between 2004 and 2023, a total of 266 listeriosis cases, with an average annual incidence rate of 1.23 cases per 1,000,000 population, were reported; a significant surge in cases was observed in 2023, with the incidence rate reaching 3.0 cases per 1,000,000 population [46,47]. These developments highlight significant challenges for both the food industry and public health authorities. European Regulation (EC) No 2073/2005 imposes strict safety criteria for specific microorganisms in RTE foods, including \(Lm\)[48]. The regulation outlines microbiological criteria based on factors like the pH and water activity (a\({}_{\text{w}}\)) of the food, which influence the growth of \(Lm\). Foods with a pH \(\leq\) 4.4, a\({}_{\text{w}}\)\(\leq\) 0.92, a combination of pH \(\leq\) 5.0 and a\({}_{\text{w}}\)\(\leq\) 0.94, or a shelf life shorter than five days are considered safe, as long as \(Lm\) levels do not exceed 100 CFU/g during the product's shelf life. For RTE foods capable of supporting \(Lm\) growth, stricter measures are required. Food business operators (FBOs) must demonstrate that \(Lm\) levels will remain below 100 CFU/g throughout the product's shelf life or test for the absence of \(Lm\) in a 25 g sample. If neither is possible, the regulation mandates the implementation of science-based approaches, including challenge tests and durability studies, to ensure that \(Lm\) growth is controlled. These studies encompass all stages of food production, processing, distribution, and consumer use. Numerous studies have been conducted on monitoring \(Lm\) growth in RTE foods [49, 50, 51, 52, 53, 54]. Commission Regulation (EU) 2024/2895 of 20 November 2024 amends the Regulation (EC) No 2073/2005 as regards \(Lm\) and tightens microbiological criteria for \(Lm\) in ready-to-eat (RTE) foods that support its growth. Specifically, it mandates that if a food business operator cannot demonstrate that \(Lm\) levels will remain below 100 CFU/g throughout the food's shelf life, the \"not detectable in 25 g\" criterion must be met for the entire shelf life, not just at the manufacturing stage [48]. This effectively increases safety standards and potentially impacts shelf life management for affected RTE products.