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Tibetan medicinal plants have been used for more than 2 000 years. In order to find their differences in antioxidant activity, total phenolics and total flavonoids between "hot-nature" and "cold-nature" herbs, we investigated the antioxidant activities of 40 Tibetan herbs from Qinghai plateau, with 20 herbs in cold-nature and 20 herbs in hot-nature. Antioxidant capacities were evaluated by the following methods: scavenging ABTS•(+) (2, 2'azinobis-(3-ethylbenz-thiazoline-6-sulfonic acid), scavenging O2•(-), and Ferric-reducing antioxidant power (FRAP). The effects on inhibition of mitochondrion lipid peroxidation were determined by measuring the formation of TBARS (Thiobarbituric acid reactive substrates). Total phenolics and flavonoids were estimated by Folin-Ciocalteu and NaNO2-Al(NO3)3-NaOH colorimetric methods. Interestingly, the cold-nature herbs displayed higher antioxidant activities than the hot-nature ones, corresponding to nearly three-fold higher total phenolic contents in the cold-nature herbs. Moreover, the antioxidant activities correlated linearly with the levels of total phenolics for both cold-nature and hot-nature herbs, but only with the levels of total flavonoids for the hot-nature herbs. The results suggested that the phenolic compounds, but not the flavonoids, play the major role in antioxidant capacities of the cold-nature herbs. These findings could shed new lights on the study the theory of Tibetan medicine.
The essential oil of Tibetan medicine Dracocephalum heterophyllum Benth was obtained by hydrodistillation with a 0.7% (v/w) yield. The chemical composition of the essential oil was analyzed by gas chromatography-mass spectral (GC-MS). Eighty-three compounds, constituting about 89.83% of the total oil, were identified. The main compound in the oil were Cineole (14.89%), trans-nerolido (7.10%), 1-m-ethyl-2-(1-methylethyl)-benzene (4.42%), Germacrene-D (4.84%), Decahydro-1,1,4,7-tetramethyl-4aH-cycloprop[e]azulen-4a-ol (4.94%), p-menth-1-en-4-ol,acetate (4.34%), 4-methyl-1-(1-methylethyl)-3-cyclohexen-1-ol (4.10%). The antimicrobial activity of the oil was evaluated against nine bacterial, one yeast, and three fungi. The antimicrobial test result showed that the essential oil strongly inhibited the growth of test microorganisms studied. The maximal inhibition zones and MIC values for bacterial, yeast and fungi strain were in the range of 18-25 mm and 0.039-0.156 mg mL(-1); *20 mm, and 0.156 mg mL(-1); 8-24 mm and 0.313-2.5 mg mL(-1); respectively. The antioxidant activity of the oil was determined by the malonyldialdehyde (MDA) test, measuring the MDA concentration in mouse liver cell microsomal after induced lipid peroxidation using FeSO(4) and ascorbic acid, The inhibition of lipid peroxidation was 59.3% with a concentration of 0.5 mg mL(-1). Result presented here may suggest that the essential oil of D. heterophyllum posses antimicrobial and antioxidant properties, and therefore, they can be one of new medicinal resources for antimicrobial agent and/or used as a natural preservative ingredient in food and cosmetics and pharmaceuticals industry.