Preparation and characterization of molecular weight fractions of guar galactomannans using acid and enzymatic hydrolysis

A procedure is described for the preparation of large amounts of guar galactomannan by acid hydrolysis that yields samples of various molecular weights (MW) with uniform polydispersity. This contrasts with preparation by enzymatic degradation that yields samples with a marked increase in polydispersity and a much broader molecular weight distribution (MWD). Acid hydrolyzed guar samples had a Mark-Houwink-Sakurada (MHS) relationship of [η]=3.04×10^-4 M_w^0.747 dl/g and a characteristic ratio of 11.87 as determined by gel permeation chromatography (GPC) and dilute solution viscometry. The Huggins coefficient for degraded guars is much smaller (∼0.4) than that of the native guar (∼0.79), suggesting a weakening of intermolecular association in guar prepared by acid hydrolysis.