Antioxidant activity and α-amylase inhibitory effect of selected medicinal plants grown in Jordan : an in-vitro study

الملخص EN

Background / aim Olive tree (Olea europaea), Artemisia herba-alba, Rosmarinus officinalis, and Teucrium polium are among the medicinal plants grown in Jordan and used in folk medicine to reduce the complication of diabetes.

This study aimed to evaluate the antioxidant activity and inhibitory activity of phenolics and porcine pancreas α-amylase, in vitro, of these medicinal plants.

Materials and methods The plant materials of A.

herba-alba, O.

europaea, R.

officinalis, and T.

polium were purchased from the local market in Amman.

The aqueous extracts of aerial parts were investigated for the total phenolics and flavonoidal contents spectrophotometrically.

Antioxidant activity was determined by two methods: 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and reducing power activity using ferricyanide assays.

α-Amylase inhibitory activity was determined using 2-chloro-4-nitrophenyl-α-d-maltotrioside (CNP-G3) assay in vitro.

Results Aqueous extract of R.

officinalis was the highest in phenolic and flavonoidal contents (107.6mg gallic acid equivalent/100 g and 482mg quercetin equivalent/ 100 g, respectively) among other three extracts, and it has the highest reducing power and DPPH inhibition activities at concentration of 25 ppm (30.9 and 57.3%, respectively).

Moreover, it showed a remarkable α-amylase inhibitory activity (70% at a concentration of 20 μg/ml).

T.

polium aqueous extract showed to contain the least amounts of phenolics and flavonoidal compounds of 43.4mg gallic acid equivalent /100 g and 206.0mg quercetin equivalent/100 g, respectively; the lowest reducing power and DPPH inhibition activities of 14.8 and 38.3%, respectively, at concentration of 25 ppm; and weak α-amylase inhibitory activity (5% at a concentration of 20 μg/ml).

However, all extracts including O.

europaea and A.

herba-alba showed a potential antioxidant activity better than the standard BHT (butylated hydroxytoluene) on DPPH (2,2-diphenyl-1-picrylhydrazy) radical scavenging assay.

Phenolic compounds from the studied plants showed strong and significant correlation with both reducing power activity (r=0.92, P<0.01) and α-amylase inhibitory activity (r=0.98, P<0.01) at 180 s.

Conclusion Aqueous extract of R.

officinalis, olive tree leaves (O.

europaea), and A.

herba-alba may be suggested as potential sources of natural antioxidants and α-amylase inhibitory activity owing to their high phenolic and flavonoidal contents