Control of Listeria monocytogenes by Antimicrobial Edible Films on Ham Slices and Microwave Reheating of Frankfurters

Introduction: Antimicrobial packaging may be used to control Listeria monocytogenes on post-processed contaminated Ready-To-Eat (RTE) meat products. 

Purpose: (i) To evaluate the efficacy of edible films (EFs) containing commercial (traditional) alcoholic distillates (ADs) to inhibit growth of L. monocytogenes on ham slices and (ii) To evaluate the impact of EFs with ADs followed by microwave reheating on the reduction of pathogen on frankfurters.

Methods: Ham slices (three/package; 10x10 cm) and frankfurters (two/package; 5 cm length x 2 cm diameter) were inoculated with 2.0 to 3.0 log CFU/cm² of a 4-strain composite of L. monocytogenes. Alginate-Na (1.5% v/v) EFs were immersed in pure ethanol (40% v/v), or traditional ADs (39-41% alcohol), namely ‘raki’, ‘tsipouro’, and ‘ouzo’ for 3 min. Samples without EFs or with EFs but without ADs or ethanol were used as controls. Frankfurters were placed between two EFs, while one EF was placed between two ham slices. Samples were packaged under vacuum and stored at 4 and 10°C (n=4). Frankfurters were placed in containers with water (200 ml) and reheated in microwave (1000W/60 sec; 56±2°C) on days 0, 20 and 40 or 0, 9 and 15 during storage at 4°C or 10°C, respectively. 

Results: On ham slices, all EFs with ADs caused maintained levels of L. monocytogenes at least 5.0 log CFU/cm² lower (P < 0.05) than the controls after 80 and 50 days at 4 and 10°C, respectively. On frankfurters treated with EF-ADs, L. monocytogenes population remained 4.0-4.5 log CFU/cm² lower (P < 0.05) than controls after 40 days of storage at 4°C, while at 10°C, limited growth suppression of 0.8-2.0 log CFU/cm² was observed after 15 days. Unlike 10°C, survivors of L. monocytogenes on EF with ADs frankfurters stored at 4°C and reheated in microwave, increased by 1.5-2.5 log CFU/cm² by day 40 compared to the day of packaging (day 0). Notably, the initial thermotolerance of controls remained unchanged (2.5 log CFU/cm²; P ≥ 0.05) throughout storage. 

Significance: Food safety regulations enabling antimicrobial interventions for the safety of RTE meat products should ensure both low levels of L. monocytogenes during storage and minimum tolerance to recommended consumer practices, such as microwave reheating.