Abstract
Thymus schimperi Ronniger is a wild endemic herb to Ethiopia, and is traditionally used as food flavoring, preservative as well as medicinal ingredient. This paper reports the total phenolic and flavonoid contents, antioxidant capacity and α-amylase inhibition activity of various solvent extracts of the dried leaves. The acetone extracts contained the highest total phenolic content (122.0±11.6 mg GAE/g). Total flavonoid content was the highest in methanol extract (45.1±2.9 mg QRE/g). The aqueous methanol extract showed the highest 2,2-diphenylpicrylhydrazyl (DPPH) radical scavenging ability (IC50 =11.0±1.0 µg/ml), iron reducing power (60.1±1.0 mg AAE/g), and total antioxidant capacity (1.1±0.1 mg BHTE/g). The water extract exhibited the highest iron chelating activity (IC50 = 65.4±1.1 µg/ml) while the methanol extract exhibited the highest percentage of α-amylase inhibition activity (IC50 = 335. 6±90.4 µg/ml). Except for iron chelating activity, all antioxidant activities were positively correlated with total phenolic and flavonoid contents. The study revealed that antioxidant and α-amylase inhibitory activities of the crude extract were variable when extracted by different solvents indicating a high potential to be used as natural antioxidants in food preservation as well as for preventing oxidative stress mediated human disorders. Key words: Antioxidant activity, α-amylase, BHT, phenolic, Thymus schimperi Ronniger, thyme.
Highlights
Dietary herbs have been added to foods since ancient times as flavoring agents and preservatives
Gallic acid, butylated hydroxytoluene (BHT), Folin–Ciocalteu reagent, 2,2-diphenyl-1-picrylhydrazyl (DPPH), quercetin, catechin, ferrozine, L-ascorbic acid, 3,5-dintrosalicylic acid (DNSA), and αamylase were purchased from Sigma-Aldrich
The results revealed that T. schimperi leaf extracts inhibited α-amylase in a dosedependent manner (10–2.5x103 μg/ml)
Summary
Dietary herbs have been added to foods since ancient times as flavoring agents and preservatives. They show potential health benefits as they possess antioxidant activities (Iris et al, 2006; Hui-Yin et al, 2007). Med. Plants Res. foods by preventing rancidity (Kathirvel and Rupasinghe, 2012; Gebrehana and Shimelis, 2013) and the growth of microorganisms (Bin et al, 2011; Gian et al, 2011) due to the presence of specific phytochemicals. Many studies have been conducted on bioactive phytochemicals and their effects on human health. Researches have focused on antioxidants, hypoglycemic agents (Adeneye et al, 2008), and anticancer agents (Milos et al, 2014) from natural products
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