Total phenolic content and anti-diabetic activity of dried and fresh leaves of Ocimum sanctum (Linn)

Plants are rich sources of secondary metabolites and oils which are of medicinal importance. At present, the level of acceptance of herbal medicines is increasing and replacing modern medicines due to the plant safety, efficiency, low cost and availability throughout the world. Leaves of Ocimum sanctum (Linn) have been proven to possess anti -diabetic effects in experimental animals, but the mechanism of anti-diabetic remains indeterminate. Research has been conducted to investigate the total phenolic content and anti-diabetic activity of Ocimum sanctum (Linn) dried and fresh leaves in three different extracts. A correlation between the total phenolic content and anti-diabetic activity was established. Three types of extracts, cold water, methanol and chloroform of dried and fresh leaves of Ocimum sanctum (Linn), were prepared by evaporating the extraction solvent at 40°C except for cold water extract at 50°C. Stock solutions of 10 mg/mL of each type of extract were prepared using dimethyl sulfoxide (DMSO). The folin-ciocalteu method was used to determine total phenolic content, while 3, 5-dinitro salicylic acid (DNS) method was used to determine α-amylase inhibition activity by different extracts of dried and fresh leaves. Generally, all the extracts of dried leaves of Ocimum sanctum (Linn) contain more total phenolic content and show the highest α-amylase inhibition activity as compared to fresh leaves. The highest total phenolic content and α-amylase inhibition activity were found in the methanol extracts of both dried and fresh leaves. The total phenolic content in methanol extracts of dried and fresh leaves was 0.780 mg and 0.700 mg GAE/g extract, respectively. While the percentage of inhibition of methanol extracts for dried and fresh leaves were 47% and 39.3%, respectively. The IC50 of methanol extracts of dried and fresh leaves were determined using different concentrations of methanol extracts of fresh and dried leaves (3, 6, 9, 12 mg/mL). Increasing the concentration of Ocimum sanctum (Linn) dried and fresh leaves decrease the activity of αamylase. The amount of dried and fresh leaves required to inhibit 50% of α-amylase activity was 10.4 and 11.8 mg/mL, respectively. A positive correlation was found between total phenolic content and α-amylase inhibition activity using Pearson correlation in SPSS 16.0 for dried and fresh leaves with R2 = 0.994 and R2 = 0.991, respectively. In conclusion, the methanol extract of Ocimum sanctum (Linn) dried leaves has a good potential to be used as an anti-diabetic agent.