Effect of Extraction Variables on Phenolic Content and Antibacterial Activity of Frangipani (Plumeria alba) Leaf Extract by Microwave-Assisted Extraction (MAE)

Antimicrobial resistance is a significant global health issue, prompting the search for new antibacterial sources. This study aimed to evaluate the impact of extraction parameters, such as substrate-to-solvent ratio, extraction time, and microwave power, on the yield and total phenolic content (TPC) of Plumeria alba L. leaf extracts using Microwave-Assisted Extraction (MAE) and to assess their antibacterial activity against Escherichia coli. Optimization of the extraction process involved varying solvent ratios (1:10, 1:15, 1:20 w/v), extraction times (5, 10, and 15 minutes), and microwave power levels (10%). The results showed that both yield and TPC increased with higher solvent volume and longer extraction times. The optimal conditions (1:20 solvent ratio, 15 minutes extraction time, 10% microwave power) yielded a maximum TPC of 67.98 mg GAE/g, with a significant inhibition zone of 17 mm observed on E. coli, indicating strong antibacterial activity. Phenolic and flavonoid compounds play a key role in the bioactivity, exerting effects such as protein denaturation, membrane permeability alteration, and reactive oxygen species (ROS) generation. These findings demonstrate the effectiveness of MAE in extracting bioactive compounds from P. alba leaves and establish a quantitative relationship between extraction parameters, phenolic yield, and antibacterial efficacy. This study provides a foundation for utilizing P. alba leaf biomass as a natural antibacterial agent and promoting the use of green extraction methods in phytochemical research.