Extraction optimization of total phenolics from Thai basil (Ocimum basilicum var. thyrsiflora) leaves and bioactivities of the extract

The Ocimum basilicum var. thyrsiflora leaves which contains numerous bioactive compounds has been traditionally used as medicinal herbs. Aqueous methanol extract from basil have been found to have blood sugar lowering capacity and can be used to treat patients with diabetes. In this study, different conditions were investigated to extract total phenolic content (TPC) from Thai basil leaves. Response surface methodology using Box-Behnken design was employed to optimize and determine the effects of three independent variables of extraction process, namely sample powder/solvent ratio (1/40 – 1/200 g/mL), extraction time (10 - 60 min) and temperature (45 - 65oC) on the total phenolic content. The results indicated that the selected extraction variables have significant effects on the total phenolic content. The optimal extraction condition was determined as following: sample powder/solvent ratio of 1/139 g/mL, time of 39.4 min and temperature of 51.2oC. At this condition, the total phenolic and total flavonoid contents of the extract were 41.76(+-) 0.21mg GAE/g dry weight and 10.95(+-) 0.3 mg RE/g dry weight, respectively. Its antioxidant capacity as 2,2-diphenylpicrylhyrazyl (DPPH) scavengingcapacity was 39.06 (+-)1.1%, while its inhibitory capacities against alpha-amylase and amyloglucosidase were 47.80 ± 0.93% and 24.86 ± 1.21%, respectively. As the result, the extract of Thai basil leaves exhibited fairly high antioxidant capacity and enzymatic inhibition capacities as compared to other medicinal plants. Thus, the extract of Thai basil leaves may be used as a source of bioactive compounds for health benefits. Keywords: Ocimum basilicum var. thyrsiflora, Box-Behnken design, alpha-amylase, amyloglucosidase