For centuries, aromatic herbs and spices have been added to different foods to improve the flavor and organoleptic properties. The use of aromatic plants and spices in phytotherapy is mostly related to different activities of their essential oils, such as antimicrobial, spasmolytic, carminative, hepatoprotective, antiviral, and anticarcinogenic activities. Furthermore, many studies point to strong antioxidant activities of aromatic plants and their essential oils. Knowing that phenolic compounds are the most responsible for the antioxidant activity, the amount of total phenolic contents and content of flavonoids have also been determined. In order to examine the antioxidant properties of five different extracts of Laurus nobilis L. leaves, various assays which measure free radical scavenging ability were carried out: 1,1-diphenyl-2-picrylhydrazyl, hydroxyl, superoxide anion, nitric oxide and hydroxyl radical scavenger capacity test, and lipid peroxidation assay. In all of the tests, only the EtOAc extract showed a potent antioxidant effect.

The antioxidant properties of five different extracts (Et₂O, CHCl₃, EtOAc, n-BuOH, and H₂O) of Ocimum basilicum L. and Origanum vulgare L. were studied. Antioxidant activity was assessed in six different model systems. Free radical scavenging capacity (RSC) was evaluated by measuring the scavenging capacity of extracts on DPPH, NO, O₂^·- and OH radical, as well as on hydrogen peroxide (H₂O₂). In addition, the protective effects on lipid peroxidation in liposomes (LPx) were evaluated by TBA-assay using the Fe²⁺/ascorbate induction system. The amount of total phenolic compounds and content of total flavonoids was also determined. EtOAc, n-BuOH and H₂O extracts of O. basilicum and O. vulgare expressed very strong scavenger activity. Furthermore, the mentioned extracts showed notable inhibition of LPx. On the other hand, Et₂O and CHCl₃ extracts showed much weaker effect in the neutralization of DPPH, NO and O₂^·- radicals and the neutralization of H₂O₂. When examining the production of OH radicals and inhibition of LPx, the Et₂O and CHCl₃ extracts showed weak prooxidative properties. The observed differences in antioxidant activity could be partially explained by the levels of phenolics and flavonoids in the investigated O. basilicum and O. vulgare extracts.

The in vitro and in vivo antioxidant activities of different extracts of laurel leaves were studied. Free radical scavenging capacity (RSC) was evaluated measuring the scavenging activity on the DPPH, NO, O₂^·- and OH radicals. The effects on lipid peroxidation (LP) were also evaluated. Experimental results indicate that ethyl acetate extract of leaves has exhibited the largest RSC capacity in neutralization of DPPH, NO, O₂^·- and OH radicals. The same result was obtained in investigation of extracts impact on LP. The in vivo effects were evaluated on some antioxidant systems (activities of GSHPx, LPx, Px, CAT and XOD, and GSH content) in the mice liver and blood-hemolysate after treatment with the examined laurel extracts, or in combination with carbon tetrachloride (CCl₄). On the basis of the results obtained it can be concluded that the examined extracts exhibited a certain protective effect, which is more pronounced on the liver than on blood-hemolysate parameters. The results obtained indicate toxicity of CCl₄, probably due to the radicals involved in its metabolism. Combined treatments with CCl₄ and the examined extracts showed both positive and negative synergism. Based on the experimental results, the strongest protective effect was shown by the EtOAc extract.

The essential oils of three different growth stages of Trifolium pratense L. (TP1, TP2 and TP3) were investigated by gas chromatography-mass spectrometry and tested for their antioxidant and antimicrobial activities. The highest content of volatile compounds was found in the essential oil sample TP1, where terpenes such as β-myrcene (4.55%), p-cymene (3.59%), limonene (0.86%), tetrahydroionone (1.56%) were highlighted due to their biological activity. The antioxidant activity was determined by following the scavenging capacity of the essential oils for the free radicals DPPH^·, NO^· and O₂^·-, as well as effects of the investigated oils on lipid peroxidation (LP). In all three cases, the sample TP1 showed the best radical-capturing capacity for DPPH^· (27.61 ± 0.12 µg/mL), NO^· (16.03 ± 0.11 µg/mL), O₂^·− (16.62 ± 0.29 µg/mL) and also had the best lipid peroxidation effects in the Fe²⁺/ascorbate induction system (9.35 ± 0.11 µg/mL). Antimicrobial activity was evaluated against the following bacteria cultures: Escherichia coli (ATCC10526), Salmonella typhimurium (ATCC 14028), Staphylococcus aureus (ATCC 11632) and Bacillus cereus (ATCC 10876). None of the examined essential oil samples showed inhibitory effects on the tested bacterial strains.

In order to examine the antioxidant properties of five different extracts of Trifolium pratense L. (Leguminosae) leaves, various assays which measure free radical scavenging ability were carried out: 1,1-diphenyl-2-picrylhydrazyl, hydroxyl, superoxide anion and nitric oxide radical scavenger capacity tests and lipid peroxidation assay. In all of the tests, only the H₂O and (to some extent) the EtOAc extracts showed a potent antioxidant effect compared with BHT and BHA, well-known synthetic antioxidants. In addition, in vivo experiments were conducted with antioxidant systems (activities of GSHPx, GSHR, Px, CAT, XOD, GSH content and intensity of LPx) in liver homogenate and blood of mice after their treatment with extracts of T. pratense leaves, or in combination with CCl₄. Besides, in the extracts examined the total phenolic and flavonoid amounts were also determined, together with presence of the selected flavonoids: quercetin, luteolin, apigenin, naringenin and kaempferol, which were studied using a HPLC-DAD technique. HPLC-DAD analysis showed a noticeable content of natural products according to which the examined Trifolium pratense species could well be regarded as a promising new source of bioactive natural compounds, which can be used both as a food supplement and a remedy.

The antioxidant activity of Marrubium peregrinum essential oil, collected from three different locations [Backo Gradiste - Rimski Sanac (No.1), Novi Knezevac (No.2) and Senta (No.3)] was evaluated as free radical scavenging capacity (RSC), together with inhibition on xanthine-oxidase and effects on lipid peroxidation (LP). RSC was assessed measuring the scavenging activity of the essential oils on 2,2-diphenyl-1-picrylhydrazyl (DPPH^·), super oxide anion (O₂^·-), nitric-oxide (NO^·) and hydroxyl (OH^·) radicals. The activities of xanthine-oxidase (XOD) was determined by the nitrite method. Effects on LP were evaluated by following the activities of essential oils in the Fe²⁺/ascorbate induction system. Experimental results indicate that the essential oil of M. peregrinum from Senta (No.3) exhibited the strongest inhibitory effect, as the IC₅₀ value was achieved with the lowest concentration. The same result was obtained in investigation of influence of essential oil on XOD and LP. The chemical profile of essential oil was evaluated by the means of gas chromatography-mass spectrometry (GC-MS). According to the analysis, the most powerful scavenging compounds were sesquiterpene hydrocarbons (b-caryophyllene, bicyclogermacrene and germacrene-D) and oxygenated sesquiterpenes (spathulenol and caryophyllene oxide).