Abstract
P. argentatum (guayule) is a dry climate bush producing polyisoprene (PI) having properties close to hevea's, and resin, a complex mixture of terpenics and lipids. The present work deals with (i) characterizing the biomass and (ii) extracting resin under low environmental impact conditions. This complements on the resin side previous works of the team on PI extraction with water (latex), under the framework of EU funded Eu-Pearls project and Prince of Songkla University. Chemical analysis (GC, TLC, HPLC, IR, NMR) which needed setting-up new extraction protocols, coupled to imaging techniques, shows the important variability among the 26 biomass samples of same genotype (age, place): resin content in biomass parts and composition. The ratio of unsaponifiable / saponifiable fractions is always found larger than 1; taking into account that this last fraction contains 65% of cinnamic and para-anisic acids issued from the saponification of guayulins (sesquiterpenes esters), fatty acid-containing lipids are thus minor components in resin. Argentatins (tetracyclic triterpenes ceto-alcohols, up to 83% of terpenics) are always more concentrated than guayulins; the total of the six identified terpenics makes up to 19% of resin in bark which is also the richest part in resin (10% of dry bark). The saponifiable fraction shows ten identified fatty acids (C10 to C21, mainly saturated), about the double of reported fatty acids in literature (C16 and C18, mainly unsaturated).