From volatiles to solid wastes: Towards the full valorization of lavender and rosemary by simultaneous in situ microwaves and ultrasounds irradiation extraction

Abstract

Novel green extractions aim at the full valorization of aromatic herbs along with the minimization of energy consumption, extraction time and cost of the processes. In this perspective, a simultaneous ultrasound and microwave irradiation extraction method (US-IMWAE) for the full valorization of aromatic herbs is here presented. This green approach has been applied to the isolation of essential oils (EOs), hydrosols and solid residues from lavender and rosemary plants. The yields of US-IMWAE in terms of EO weight percentage (wt%), polyphenols concentration and thermochemical characteristics of the solid residues have been compared with microwave assisted extraction (IMWAE) and hydrodistillation (HD). The composition profiles of EOs and hydrosols have been analyzed and quantified by head space gas chromatography mass spectrometry (HS-GC–MS), liquid chromatography with UV/visible diode array/fluorescence detector (HPLC-DAD-FD) and the Folin-Ciocalteu test for the total phenolic content (TPC). Solid residues as valuable by-products have been investigated by FTIR spectroscopy in tandem with chemometrics, thermogravimetric analysis (TGA) and combustion calorimetry. We found that the US-IMWAE green extraction method has produced higher yields of EOs with appealing composition profiles for cosmetic, fragrance and perfume industries (lavender), and for pharmacology and medical applications (rosemary). The high concentration of rosmarinic acid and the total phenolic content in hydrosols obtained with the US-IMWAE method, highlights its great potential. Chemometric analysis of solid residues has found that cellulose is the main component followed by hemicellulose and lignin. The experimental values of enthalpy of combustion of the solid residues (ΔcH) match with the corresponding calculated values and confirm their energetic features and their potential uses as alternative biomass for fuel production. US-IMWAE is environmentally friendly, highly flexible, controllable, and it enables to break the scale-up barrier in ultrasounds and microwave assisted industrial processes. Thus, US-IMWAE has a great potential to reduce EO production costs, and to increase local farm income through the full exploitation of aromatic herbs.