Accurate quantification of guayule resin and rubber requires sample drying below a critical temperature threshold

To accurately quantify secondary products in plant materials, using solvent extraction, harvested plant materials must be dried and ground without altering the amount and, preferably, the composition of the compounds of interest. We examined the effect of pre-extraction drying temperatures and times on the acetone and hexane-extractable components of guayule, resin and rubber, respectively. Drying guayule samples at 50 degrees C prior to extraction did not alter subsequent extractions of resin and rubber. However. drying temperatures of 75 degrees C, and above, degraded guayule rubber into acetone-soluble fragments. The total amount of acetone and hexane extractable material remained constant up to 150 degrees C. However, the acetone and hexane soluble materials were progressively volatilized at 200 degrees C. We predict that the sensitivity of secondary products to drying temperatures in not confined to guayule and suggest that plant drying temperatures should be carefully evaluated for their impacts on the quantity and composition of analytes. (C) 2012 Published by Elsevier B.V.