STUDIES ON SOIL POLYSACCHARIDES .I. ISOLATION OF POLYSACCHARIDES FROM SOIL

Methods for extracting polysaccharides from soil have been evaluated with respect to yield and polymer degradation. Maximum extraction with a single non-degradative treatment was obtained by shaking soil with 0.5N NaOH for 16 hr at 20 °C. Pretreatment of the soil with cold dilute hydrochloric and hydrofluoric acids raised the extraction efficiency to over 40% of the total soil carbohydrate. The carbohydrates removed by 0.5N NaOH at 20 °C and by hot water and other lower-yielding reagents were of comparable molecular size. Hot 0.5N NaOH treatment and acidic acetylation both removed more carbohydrate than cold 0.5N NaOH but caused considerable degradation. About 80% of the carbohydrate was removed from a range of soils by extracting first with 1N HCl, followed by 0.5N NaOH, and finally acetic anhydride containing 2.5 % conc. H2SO4. Humic materials were removed from the 0.5N NaOH by passing the extract upwards through a column of Dowex 50 (H+). Other coloured materials were adsorbed from the effluent by a water-insoluble cross-linked polyvinyl-pyrrolidone, and final purification and desalting were achieved by gel filtration. The 'purified' polysaccharide contained neutral sugars 55%, hexosamines 6%, uronic acids 10% (minimal value), amino acids 6 %, nitrogen 2.1%, and ash 1.8%. At least 10 neutral sugars, 2 hexosamines, 2 uronic acids, and 16 amino acids were present. The polysaccharides had a wide molecular weight distribution. © 1968 CSIRO. All rights reserved.