Optimization of microwave-assisted extraction of phenolic compounds from Ocimum gratissimum leaves and its LC–ESI–MS/MS profiling, antioxidant and antimicrobial activities

Phenolic compounds are essential for growth, pigmentation, resistance to pathogens, reproduction, and among others. This study focused on the optimization of microwave-assisted extraction process variables, i.e., solvent/sample ratio (X1), irradiation time (X2) and microwave power (X3), based on the yields of total phenolic content (TPC) and total flavonoid content (TFC) from Ocimum gratissimum leaf using Box Behnken Design. Furthermore, the chemical compounds in the extract under optimized MAE conditions were identified using LC–ESI–MS/MS analysis; its antioxidant and antibacterial properties were evaluated as well, and optimal MAE conditions, i.e., X1 = 10:1 mL/g, X2 = 3 min and X3 = 553 W, were obtained with TPC and TFC yields of 184.99 ± 3.05 (mg GAE/g extract) and 68.78 ± 2.07 (mg QE/g extract), respectively. The results indicated that the leaf extract of O. gratissimum possesses antioxidant and antibacterial properties. Aside from these, the LC–ESI–MS/MS analysis provided tentative identification of 131 phenolic and other phytochemical compounds in the leaf extract at optimized conditions. The extract showed higher inhibitory activities against all the considered bacteria organisms (at least the concentration of 15 mg/mL). Thus, O. gratissimum leaf can be employed as an industrial crop with potential usage in the nutraceutical and food products.