Essential Oils from Thymus capitatus and Thymus algeriensis as Antimicrobial Agents to Control Pathogenic and Spoilage Bacteria in Ground Meat

The antibacterial effects of essential oils (EOs) extracted from Thymus capitatus and Thymus algeriensis were assessed and evaluated against four pathogenic bacteria (Escherichia coli (ATCC 25922), Listeria monocytogenes (ATCC 19118), Staphylococcus aureus (ATCC 25923), and Salmonella typhimurium (ATCC 1402)) and one spoilage bacterium (Pseudomonas aeruginosa (ATCC 27853)). Both investigated EOs presented significant antimicrobial activities against all tested bacteria with a greater antibacterial effect of T. capitatus EO. In fact, the results indicated that the minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs) of T. capitatus EO are in the range of 0.006–0.012% and 0.012–0.025%, respectively, while those of T. algeriensis EO ranged between 0.012 and 0.025% and 0.05%, respectively. Furthermore, the inhibitory effects of both EOs were appraised against the spoilage bacterium P. aeruginosa, inoculated in minced beef meat, at two different loads (105 and 108 CFU) mixed with different concentrations of EOs (0.01, 0.05, 1, and 3%) and stored at 4°C for 15 days. The obtained data demonstrated that the antibacterial effect of tested EOs varies significantly in regard to the levels of meat contamination and the concentrations of EOs. In fact, in the presence of 0.01 and 0.05% of oils, a decrease in bacterial growth p < 0.01 was observed; but, such an effect was more pronounced in the presence of higher concentrations of EOs (1 and 3%), regardless the level of meat contamination. Besides, at the low contamination level, both EOs exerted a rapid and a more pronounced antibacterial effect, as compared to the high contamination level. The results illustrated the efficacy of both EOs as preservatives in food against well-known pathogens of food-borne diseases and food spoilage, particularly in P. aeruginosa in beef meat. As regards sensory evaluation, the presence of T. capitatus EO proved to improve the sensory quality of minced beef meat.