Investigations on wood starches

Abstract

The difficulties encountered in preliminary investigations on wood starches are described. The presence of gallotannin, aToarently strongly adsorbe' on the granules, was found to be responsible for serious interference, particularly with the results of potentiometric iodine titration for the determina tion of amylose and with the results of periodate oxidation for the determination of the number of glucose residues in the starches per non -reducing end -group. The reactivity of gallotannin with iodine has been shown to be responsible for erroneouvalues of molecular weight determination of the starch samples by means of alkaline hypoiodite oxidation.A technique for overcoming the interference of the impurities with potentiometric iodine titrations was developed and the amylose contents of the wood starches were shown to vary between 14. and 20 ¡0Attempts to remove the impurities from the wood starch samples are described. Solvent extraction of the granules with boiling 8* aqueous methanol was found to be the most effective method of removing the reactive gallotannin without simultaneous degradation of the polysaccharides.Samples of amylose were isolated by fractionation of elm and oak sapwood starches by slow cooling of hot dispersions of the starches in 15% aqueous pyridine. The crude amyloses obtained from the initial fractionations were each repreoipitated thre times from butanol- saturated water. The amylosebutanol complexes were isolated in typical spherocrystalline form. The recovered amyloses were shown to adsorb iodine to the extent of 19-20% of their own weight.Acetylation of wood starches yielded products the general properties of which were characteristic of other similarly acetylated starches.Methylation of elm sapwood starch yielded a product which closely resembled other similarly methylated starches. The material possessed relatively high specific viscosity in m-cresol indicating a molecular weight of the order of 5 x 10⁵. Hydrolysis of methylated elm starch and chromatographic separation of the products on a cellulose column yielded a quantity of 2:3:4:6- tetramethyl glucose consistent with a repeating -unit chain- length for the amylopectin component of 20± 1 glucose residues on the basis of the Haworth-Hirst 'laminated' formula for atnylopectin.