Improving the extraction of guayulins from guayule stems (Parthenium argentatum A. Gray)

Abstract

Guayule (Parthenium argentatum A. Gray) exploitation has so far been focused on the production of rubber, but until now was unable to compete commercially, as other guayule co-products have not been equally considered for exploitation. However, to successfully exploit one of these co-products, the guayulins, it will be necessary to establish a robust resin extraction method that maximizes the yield of guayulin compounds for downstream purification. For this purpose, different resin extraction conditions (solvent, temperature, number and time of cycles, and plant material:solvent ratio) were evaluated to select those that produced a resin with a higher guayulins yield. First, accelerated solvent extraction (ASE) was performed using three solvents (ethanol, acetonitrile, and acetone) at three different temperatures (40, 56, and 80 °C) and two cycle times (5 and 20 min) to narrow down the conditions. Then, an industrial scale process was simulated with warm solvent extraction (WSE) using acetone and acetonitrile only at five different cycle times (30, 45, 60, 120, and 180 min). Finally, WSE performance was optimized using four different plant material:solvent ratios (1:20, 1:10, 1:5, and 1:3), and three consecutive extraction cycles. Results from the ASE studies revealed, as expected, that solvent choice had the greatest influence on resin and guayulins yield and allowed to discard ethanol as a suitable extraction solvent while acetonitrile performed best for guayulin extraction. No tangible differences in resin yield were observed in WSE studies between the different process parameters, but they were differences in guayulin extraction. Short cycle times worked best with both solvents, and again, acetonitrile was more selectively extracted guayulins, especially for the polar guayulins C and D. Finally, WSE optimization showed that a 1:5 plant material:solvent ratio and two extraction cycles were the best compromise in terms of guayulins yield and time/cost effectiveness.