SC-CO2 Extraction of guayule biomass (#Parthenium argentatum#) – yield and selectivity towards valuable co-products, lipids and terpenics

Guayule (Parthenium argentatum) a shrub native to Mexico, is now being acclimated in Europe as a potential crop. The main extractible fractions are polyisoprene (similar to Hevea rubber) for producing tires and allergy-free gloves and resin (GRe). This work deals with valorising this last fraction, after water-based extraction of the latex. To date GRe has not been extensively investigated, in spite of containing useful compounds, and there is a need for a green and selective extraction process, which is the aim of present work. First, resin -a mixture of lipids and terpenics- was analysed with focus on fatty acids and other carboxylic acid containing classes. Then the influence of extraction conditions was investigated, under "soft" conditions with supercritical carbon dioxide (SC-CO₂). Investigated parameters act on extraction efficiency (yield, selectivity) towards valuable fractions. Our results do show that SC-CO₂ alone cannot extract substantial amounts of resin. As co-solvent, ethanol -a benign one- and acetone, this last being the most common solvent for that purpose, here also used alone as reference, under pressurized extractions conditions (ASE). Under SC-CO₂, ethanol allows the highest resin yield (12.1%-dw biomass dry weight) compared to acetone (7.0%-dw) and to the reference ASE-acetone method (5.2%-dw). Found suitable conditions with SC-CO₂-ethanol are affordable: flow rate 34 gCO₂/min and 3.0mL/min of co-solvent, temperature 45°C, pressure 300 bar. Saponification was used for separating resins components before analysis. Aromatic carboxylic acids (cinnamic, panisic) initially linked to a sesquiterpene, are the major components found in G-Re from the biomass (branches) using the reference ASE method. But these are even more prominent in SC-CO₂-ethanol extracts from bagasse (68.7%), compared to SC-CO₂-acetone (51.1%) which allows a lower selectivity. The unsaponifiable fractio