Abstract
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.
Highlights
Meat and meat products represent one of the most perishable foodstuffs [1] due to their complex composition which consists of proteins, saturated and unsaturated lipids, carbohydrates, vitamins, pigments, high water content, and moderate pH [2, 3]
The results indicated that the minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs) of T. capitatus essential oils (EOs) 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
It was shown that the antioxidant activity of EO of T. capitatus exhibits higher antiradical activity with an IC50 value of 213.53 μg/ml than that of T. algeriensis showing an IC50 value of 861.12 μg/ml, butylated hydroxytoluene (BHT) presenting an IC50 value of 30 ± 0.01 μg/ml (Table 1). ese results agreed with those of Amarti et al [26], who showed that T. capitatus EOs possess strong antioxidant activities with IC50 equal to 69.04 μg/ml
Summary
Meat and meat products represent one of the most perishable foodstuffs [1] due to their complex composition which consists of proteins, saturated and unsaturated lipids, carbohydrates, vitamins, pigments, high water content, and moderate pH [2, 3]. E breakdown of fats, proteins, and carbohydrates in meat leads to the formation of off-odors, off-flavors, and slime formation, rendering meat unacceptable for Journal of Food Quality the consumer [5,6,7]. Pseudomonas causes meat and meat product spoilage and develops repulsive characteristics as putrefaction of proteins and lipids with changes in pH continue [10, 11]. Grinding has several detrimental effects on meat by increasing the surface area exposed to air and bacterial contaminations [12]. It increases losses of intracellular reductants as well as polyunsaturated fat, leading to deterioration of meat and the warmed-over flavors [13, 14]
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