Evaluation of the antioxidant properties and total phenolic content of a dairy product (yogurt) supplemented with Thymus willdenowii essential oil from Algeria.

The purpose of this study was to evaluate the antioxidant properties and total phenolic content of a dairy product (yogurt) supplemented with Thymus willdenowii (synonym: Thymus hirtus) essential oil. The evaluation of the antioxidant and antibacterial activities of the oil against food spoilage bacteria and lactic acid strains was also assessed. The chemical composition of the oil was obtained by GC/MS. The evaluation of the antioxidant activity of a fortified yogurt with this oil was assessed by Oxygen radical absorbance capacity test (ORAC). The main component of the oil was Linalool (89.55%). DPPH, and Ferric reducing power revealed a weak antioxidant activity (IC₅₀ > 1600 µg/mL, > 800 µg/mL respectively) while a moderate activity was obtained with ABTS and CUPRAC tests (38.06 ± 0.30, 56.15 ± 1.07 µg/mL respectively). A high concentration of the oil is needed to delay the inhibition of the β-carotene (> 800 µg/mL). Thus, a strong antibacterial activity was observed against the pathogenic strains with the high inhibition diameter for B.cereus ATCC10876 (31.75 ± 1.50 mm) while a weak effect was observed against lactic acid bacteria. A significant decrease in the antioxidant potential of non-supplemented yogurt was observed from day 1 to 21 while there was no significant difference in ORAC of supplemented yogurt with the oil. The maximum of total phenolic content was observed in day 21 of cold storage (252.92 ± 3.01 µg GAE/mL of yogurt). The essential oil studied could be an effective natural additive to yogurt avoiding the use of synthetic preservatives. [ABSTRACT FROM AUTHOR]