An eco-extraction protocol based on blended mode microwave hydrodiffusion and gravity (MHG) principle for floral biomass valorisation through simultaneous recovery of volatile and non-volatile principles: the case of Tagetes erecta

The work showcases a strategised implementation of microwave hydrodiffusion and gravity (MHG) method where an effective blend of high- and low-power microwaves have been used for simultaneous extraction of volatile (essential oil) and non-volatile (carotenoids) class of compounds from leftover floral waste. The said blended mode completes the extraction in two phases. In the first phase sudden rupture of oil glands is facilitated due to exposure to high-power microwave. In the second phase smooth draining of essential oil occurs under gravity due to prolonged exposure of low-power microwave. The developed protocol was exhaustive in terms of extraction of tagetes essential oil (TEO) and at the same time soft enough on the biomass to preserve its carotenoid content which can be extracted post-extraction of TEO. Blended mode of operation returned better results than fixed power level. High-power surge at 680-W microwave power level for 5 min followed by continued extraction in short cycles of 5 min each at 170-W power level emerged as the optimal operating condition producing 65% more tagetone-enriched oil when compared to that obtained from steam distillation (SD). Kinetic modelling studies were carried out as well. The quantification of β-crypto-xanthene, lutein, zeaxanthin, and β-carotene was carried out for the leftover biomass post-extraction of TEO both using MHG and SD. The findings revealed that the carotenoid depletion by at least 50% occurred in the leftover biomass after SD than when compared to the biomass obtained after MHG.