Chemical characterization, antioxidant activity and morphological traits in the leaves of guayule (Parthenium argentatum A. Gray) and its hybrids

In the rubber extraction process, guayule leaves represent an important biomass waste by-product, up to 32%, whose exploitation might contribute to the valorization of the whole plant. The extraction of any of its bioactive compounds or its use as an antioxidant seems to be the most feasible alternative. This study relates guayule leaves morphology to the individual content of 35 compounds (of the 50 tentatively identified), the determination of overall phenolic content and antioxidant activity. The morphological traits allowed the classification of the accessions (27) into three main groups according to size and shape of the leaf, being related to their hybridization. The environment and growing conditions modified the leaf phenotype for USDA germplasm with respect to recent USA studies. The heterogeneity found by different authors in the determination of phenolic content in guayule leaves requires a standardization procedure. Of the two analysis protocols, Total Polyphenol Index (TPI) and Folin–Ciocalteau reagent (Folin) after extracting the leaves at 1 and 24 h, the TPI at 1 h was selected since it was faster and simpler than others and correlated better with the antioxidant activity determined by 2,2-diphenyl-picrylhydrazyl (DPPH). The compounds found in greater quantities corresponded to the chlorogenic acid family, but with no influence with leaf morphology. On the other hand, compounds with smaller concentrations such as gallic acid, an isomer of ferulic acid or the quercetagetin methyl ether glucuronide correlate with aspects of leaf morphology. ; ISSN:0926-6690 ; ISSN:1872-633X