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 terpenicswas 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 oneand 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 fraction shows a low dependency on extraction temperature with SC-CO2-ethanol, playing in favor of preserving extract value, guayulins (sesquiterpenes) and argentatins (triperpenes) being known anti-insect and fungistatic agents for wood preservation. Minor resin components are fatty acids containing lipids C18:2, C18:3, C16:0. SC-CO2 and ethanol, which can be easily recycled, are highly suitable for extracting high-value natural compounds, given their low environmental impact. This work provides the first detailed insight for selecting appropriate parameters and their variation range, in view of further optimizing a “green” process for extracting above compounds.