Solvent-free microwave extraction of essential oil from pigeon pea leaves [Cajanus cajan (L.) Millsp.] and evaluation of its antimicrobial activity

Abstract

Solvent-free microwave extraction (SFME) of essential oil from pigeon pea leaves and its antimicrobial activity were investigated. The process of SFME was optimized by a central composite design (CCD) and response surface methodology (RSM). The optimal parameters were extraction time 44min, irradiation power 660W, and humidity 68%, with extraction yield of 0.330 (%, w/w). The main constituents were sesquiterpenes (72.89%), including α-copaene (5.89%), β-caryophyllene (7.46%), α-himachalene (12.97%), α-humulene (17.43%), alloaromadendrene (8.45%), and α-bisabolene (12.64%). The essential oil showed stronger antimicrobial activity against Bacillus subtilis and Propionibacterium acnes with MIC and MBC values 1.06mg/mL and 2.12mg/mL, 0.13mg/mL and 0.26mg/mL, respectively. These results indicated that SFME method was an outstanding alternative for the extraction of essential oil from pigeon pea leaves, and the essential oil was a potential source of natural antimicrobial.