Biochemical studies on some plants’ extracts

Aromatic and medicinal plants are rich sources of phenolic compounds with health-promoting activities. In this investigation five plants [clove (Syzygium aromaticum), rosemary (Rosmarinus oficinalis), thyme (Thymus vulgaris), sweet marjoram (Origanum majorana) and ginger (Alpinia zerumbet)] were selected to study their phenolic contents and antioxidant activities. Twenty extracts of the tested plants were obtained by using 4 different solvents (hexane, ethyl acetate, ethanol 80% and distilled water) respectively using the same amount of plant. Total phenolic compounds and total flavonoids were measured using Folin–Ciocalteu reagent and AlCl3, respectively. The best amount of total phenolic compounds was obtained in hexane extract of clove and the best amount of flavonoids was obtained in hexane extract of sweet marjoram. In addition, total antioxidant capacity of the extracts was estimated by different methods including: DPPH (1,1-diphenyl-2 picrylhydrazyl radical), ABTS•+ (2, 2` azino bis-(3-ethylbenzthiazoline-6-sulfonic acid), and β-carotene/linoleic bleaching test.Clove extracts exhibited the strongest antioxidant capacity in all used assays, followed by rosemary and thyme extracts. In general, ethanol, water and hexane extracts showed comparable activity to the synthetic antioxidants TBHQ.Antibacterial activity for tested extracts was assayed by using disc assay for Gram positive and Gram negative bacteria. Tested extracts had minimal inhibition concentration (MIC) and minimal bactericidal concentration (MBC) with tested bacteria.