Optimization of Plectranthus amboinicus extraction using microwave-assisted technique

Abstract

Plectranthus amboinicus (Lour.) Spreng is a medicinal herb with bioactive compounds which has been known to have pharmacological properties that can be found throughout the tropical countries and Middle East regions like India, Asia and Australia. It has an aromatic nature and has a capability in producing essential oil. Microwave-assisted extraction (MAE) has been known as a technique for extracting essential oil with lots of benefits such as decrease extraction time, less volume of solvent used, high yield of extract and lowered the environmental impact by emitting less CO2 in the atmosphere compared to other conventional extraction methods such as soxhlet extraction method. The objective of this study was to determine the optimum extraction condition of essential oil from P. amboinicus by using MAE. This study focused on the comparison of the optimum extraction of P. amboinicus using ethanol and water by maximising the essential oil yield using response surface methodology (RSM). From the optimum extraction condition obtained, analyses on phenolic content, refractive index, bioactive compounds and antioxidants activity of the P. amboinicus extract were performed. Result showed the optimum condition for ethanol extract was at irradiation time (2 min), ethanol concentration (30%) and solvent-to-solid ratio (30 ml/g) with yield of extract obtained at 39.81% w/w and the optimum condition for water extract was at irradiation time (10 min), microwave power (529.58 w) and solvent-to-solid ratio (16.95 ml/g) with yield of extract obtained at 31.89% w/w. Meanwhile, the result analysis of total phenolic content of P. amboinicus for ethanol extract was 12.22 ± 0.93 mg GAE/g FW and for water extract was 9.61 ± 1.56 mg GAE/g FW while the antioxidants of the P. amboinicus extract of IC50 value for ethanol extract was 4.63 mg/ml while the inhibition of DPPH radical scavenging activity was 5.48 ± 0.77 mg Trolox eq/g extract. Refractive index for P. amboinicus extract for ethanol extract was 1.3622 ± 0.0006 while for water extract was 1.3492 ± 0.0021 at 20°C. Analysis of bioactive in ethanol extract comprised of a-Terpinene, carvacrol, a-Terpineol, thymol, trans-a-Bergamotene whereas for water extract consisted of ?-Cymene, a-Terpinene, a-Terpineol and thymol. The study has proven that MAE is a better alternative compared to conventional extraction method with 15% higher yield and the extract of P. amboinicus can be potentially applied in healthcare and pharmaceutical industry.