Application of central composite design and response surface methodology for optimizing microwave assisted hydrodistillation of essential oil from Curcuma amada rhizomes

Traditional methods of essential oil (EO) extraction are often associated with low yields, high energy consumption, and extended processing times, demanding the need for greener and more efficient alternatives. Thus, the present study optimized microwave assisted hydrodistillation (MAHD) for the extraction of Curcuma amada rhizome essential oil (CAREO) by evaluating the effects of microwave power, liquid-to-plant material ratio, and extraction time using central composite design of response surface methodology. The developed quadratic model (p < 0.0001, R² = 0.9966) was statistically significant, demonstrating a strong correlation between experimental and predicted responses. The optimized conditions (microwave power: 800 W, liquid to plant ratio: 2.5 mL/g, extraction time: 50 min) produced slightly higher essential oil yield (0.7 % (v/w)) than conventional hydrodistillation (HD, 0.6 % (v/w)). Both methods produced essential oils with comparable physical properties, but MAHD offered faster extraction, lower energy use, and reduced CO₂ emissions. Furthermore, GC-MS analysis revealed that the EOs obtained via MAHD and HD represented 98.62 and 97.47 % of CAREO composition, respectively. Moreover, both methods produced EO rich in monoterpene hydrocarbons with myrcene as the major constituent. FTIR spectral analysis showed no significant differences in functional groups indicating that both preserve the chemical integrity of EO components. However, SEM analysis revealed significant shrinkage of parenchymatous cells with greater loss of starch granules, thus, facilitating more release of oil in MAHD. Furthermore, MAHD was found to be more sustainable when assessed using AGREEprep and BAGI pictograms. Lastly, MAHD demonstrated higher DPPH and ABTS radical scavenging effects than HD. Overall, MAHD offers a viable eco-friendly option for CAREO extraction due to better extraction efficiency, higher yield and stronger antioxidant activity.