Influence of shading on essential oil content, composition and antioxidant activity in medical and aromatic plants

Ocimum basilicum L. (sweet basil), Origanum vulgare L. (oregano), Origanum majorana L. (marjoram), Mentha piperita L. (mint), Thymus vulgaris L. (thyme), and Melissa officinalis L. (lemon balm) as medical and aromatic plants (MAPs), were used to determine whether shading conditions could improve the yield, composition and antioxidant activity of their essential oils (EOs) in comparison with non-shaded plants from an open field. The yield of EOs after 120 min of hydrodistillation of non-shaded sweet basil, oregano, marjoram, mint, thyme, and lemon balm was 1.12, 0.21, 1.51, 2.00, 2.32, 0.18 mL 100 g, respectively, while shading caused production of higher EOs (1.32, 0.35, 1.68, 2.23, 2.57, 0.22 mL 100 g, respectively) in the studied plants. GC/MS and GC/FID analyses were applied for essential oils determinations. Basil essential oil consisted of the following components: linalool (9.06-10.2%); 1,8 cineole (1.26-8.06%) and α-trans bergamotene (1.21-1.47%). Marjoram main components were terpinene 4-ol (7.44-7.63%), c-terpinene (2.82-2.86%) and linalool (2.04-2.65%). Oregano essential oil consisted of the following components: caryophyllene oxide (3.1-1.93%); germacrene D (1.17-2.0%) and (E)-caryophyllene (1.48-1.1%). Predominant components of mint essential oil were piperitenone oxide (12.0-14.0%) and 1,8 cineole (1.32-2.27%). The main components of the thyme essential oil were thymol (8.05-9.35 mg mL); γ-terpinene (3.49-4.04%) and p-cymene (2.80-3.60%). The main components of the lemon balm essential oil were: geranial (6.84-7.78%); neral (3.02-3.52%) and piperitenone oxide (1.67-5.36%).The essential oil from shaded basil and thyme contained the highest antioxidant activity than the other plants after 20 min of incubation (EC50 value 0.68 and 0.85 mg mL). At same time, non-shaded basil and thyme contained lower antioxidant activity (EC50 0.76 and 0.94 mg mL, respectively). MAPs are a good source of natural antioxidants with potential application in the food and pharmaceutical industries. MAPs can be recommended to grow in shading conditions for achieving optimal quality parameters.