New strategies to analyze argentatins A and B in guayule (Parthenium argentatum, A. Gray).

There is considerable interest in the exploitation of compounds belonging to the triterpenoid family from guayule (Parthenium argentatum, A. Gray), as they offer several beneficial effects to human health. The most abundant triterpenoids in guayule resin are the argentatins, which are currently analyzed by labor-intensive and time-consuming techniques. The purpose of the present study was to estimate argentatins and isoargentatins A and B in guayule using near-infrared spectroscopy (NIRS) and flow injection analysis (FIA). Results revealed that the best partial least squares regression model exhibited excellent correlation with the values estimated by NIRS calibration (r2c = 0.99-1.00) and cross-validation (r2cv = 0.94-0.99), and the residual predictive deviation was >3 in all cases. After optimization of the liquid chromatography-mass spectrometry and FIA parameters, the FIA mode could reliably collect data for argentatin A and B after applying a calculated coverage factor. In sum, NIRS and FIA appear to be a robust option for the estimation and routine analysis of argentatins in guayule stems and resin, respectively.

Adapting the Accelerated Solvent Extraction Method for Resin and Rubber Determination in Guayule Using the BÜCHI Speed Extractor.

Guayule (Parthenium argentatum Gray) is a promising alternative source to Hevea brasiliensis for the production of natural rubber, which can reach levels of 8-9% under industrialized farming conditions. The most common method for determining rubber concentration is by accelerated solvent extraction (ASE), a technique developed by the Dionex Corporation and almost exclusively performed with the Dionex ASE-200 or 350 systems. Herein, it is sought to apply and adapt the most common methods used in the literature for the Dionex system to another extraction platform, the BÜCHI Speed Extractor E-914. Results showed that using a sand sandwich method to confine the sample in the center and exploiting a larger cell volume (80 mL) for extraction prevents the occurrence of overpressure and problems with clogging. Under optimized conditions, the coefficient of variation was <15% for both resin quantification for samples containing 5.0-15.8% of resin and for rubber quantification for samples with 1.7-10.3% rubber content. The extraction time for resin (2 cycles of 5 min each) was smaller than for rubber (2 cycles of 20 min each). It would be interesting to carry out interlaboratory comparisons to standardize the method at an international level.