Rapid and complete removal of guayule (Parthenium argentatum) leaves by cryodefoliation, and freeze and thaw induction of rubber particle coagulation

Abstract

Production of natural rubber (NR), a vital natural resource for modern economies, currently is completely dependent upon tropical cultivation of the Para rubber tree (Hevea brasiliensis, Müll. Arg). One promising source of alternative rubber is guayule (Parthenium argentatum, Gray), which is currently being developed as an alternative source of NR. Guayule rubber accumulates as rubber particles in bark parenchyma and can be extracted in the form of latex by homogenizing the bark and then separating the latex from the non-latex components by centrifugation. Latex separation and purification processes are significantly hindered by fine solids from the co-homogenized leaves. Therefore, complete removal of leaves before homogenization is highly desired. However, guayule leaves do not naturally abscise and chemical defoliants cannot be utilized since these dehydrate the shrub and coagulate the latex, and physical leaf removal processes are tedious or inefficient. We demonstrate that liquid nitrogen can be used to embrittle the leaves without freezing the bark parenchyma, completely removing the leaves with a single physical blow, and then the defoliated branches can be homogenized with no loss of latex-containing bark and no leaf contamination. Under longer freezing times, rubber coagulation occurred in partially frozen tissue and during slow thawing. Furthermore, we demonstrate that the rubber coagulation, which occurs when guayule branches are frozen through and thawed before homogenization, can be avoided by rapid homogenization of the flash frozen branches in ambient temperature aqueous extraction buffer.