Future trends for the analysis of guayulins in guayule (Parthenium argentatum Gray) resins

Abstract

Guayule (Parthenium argentatum Gray) is a promising alternative and renewable source of natural rubber/latex. There is a general acceptance that to successfully industrialize the cultivation of guayule, it will be necessary to valorize all of its co-products, including resins, which can reach 16 % of weight of dry matter. Guayule resins have been reported to have antifungal, insect antifeedant and wood protector activities, although it remains to be clearly established which compounds are responsible for such actions. Here, we focus on a terpene family present in guayule resin that is a candidate for these activities, the sesquiterpenes, which are present in significant amounts (10–15 %). We studies the versatility of the most common analytical method used in their analysis, HPLC-UV, with mass spectrometry techniques including LC–MS, ESI-TOF and MALDI-TOF to address the following objectives: 1) to explore whether there are other members of the guayulins family, 2) to determine the applicability of new methods based on mass spectrometry, and 3) to establish the relationship between the four known major guayulins in the seasonal changes described by other authors. Our results have allowed us to: tentatively identify a new member of this family and to suggest the existence of others; propose changes to the chromatographic approaches currently used; extend the use of mass spectrometry (direct identification and monitoring of purification of guayulins); and finally, demonstrate that the content of guayulins A and B decreases at the start of winter when the most active period of natural rubber biosynthesis begins.