Extraction of natural rubber and resin from guayule using an accelerated solvent extractor

Accelerated solvent extraction is a relatively rapid automated method for extracting compounds of interest from plant materials. We have developed a sequential solvent extraction method that can be used to accurately quantify the rubber and resin in samples of guayule (Parthenium argentatum Gray), a new industrial crop now in commercial production in Arizona, USA. The method assumes that the sample has been dried under suitable drying conditions. The ASE method requires the resin extraction protocol (three 20-min cycles) to be performed first, in gaseous N2 and at 40 °C. Higher temperatures degrade the thermolabile rubber made by guayule to acetone soluble fragments. Thus, acetone temperatures above 40 °C overestimate the resin fraction and underestimate the rubber fraction in the samples being analyzed. Following removal of the resin fraction, samples are then extracted with either cyclohexane or hexane at 140 °C. Cooler temperatures do not fully solubilize the high molecular weight guayule rubber in the three 20-min cycles. Quantification of the two extracted analytes can be performed gravimetrically, as we did in this paper, or using spectrophotometric methods. Although this high rubber extraction temperature results in good rubber quantification, the partial degradation that occurs prevents accurate molecular weight determination.

► An accelerated solvent extraction (ASE) method has been developed and validated to accurately quantify resin and rubber in guayule.
► An acetone temperature that is too hot and a cyclohexane temperature that is too cold will radically change the rubber quantification results.
► A recommended guayule sample preparation for ASE extraction is presented in the article.
► We recommend an ASE method for guayule of three extractions with acetone at 40 °C and three extractions in hexane or cylcohexane at 140 °C.
► High temperature rubber extraction results in good rubber quantification, but does not allow for accurate molecular weight determination.