Levulins and Inulin in Guayule, Parthenium argentatum A. Gray

Abstract

The presence of levulins in guayule tissues in addition to inulin previously reported, and in relatively greater amts., has been established. Thus the McRary-Slattery assumption that sucrose is a major reserve carbohydrate associated with inulin in guayule tissues has been shown to be untenable. If sucrose should be present at all, it would constitute only a minor fraction of the total carbohydrate reserves. The levulins may be fractionated into 2 major portions by extraction of guayule tissues with 89% ethanol: (a) the 89% ethanol-soluble fraction, and (b) the 89% ethanol-insoluble fraction. On the basis of this fact, a method has been devised for use in seasonal physiol. studies to determine the absolute and relative proportions of the 2 fractions in response to environmental factors. The method is a more dynamic tool for such studies than the mere recording of total residues. On the basis of diffusion coeffs., it has been shown that Pringsheim''s hypothesis for the presence of an homologous series of polymers between inulin and the monosaccharides does not hold for guayule; and that apparently difructose anhydrides are not present in guayule plants although reported in girasole tubers, Helianthus tuberosus, also a Composite, by Schlubach and Knoop. The levulins are the chief reserve carbohydrates in the guayule plant and inulin is secondary in importance from that standpoint. Although, under the experimental conditions, top invertase hydrolyzed from 30 to 65% more of the levulins extracted from guayule tissues than were hydrolyzed by invertase of bottom fermentation, treatment with 1% HC1 was required to obtain complete hydrolysis of the levulins.