Studies on hemicelluloses

Abstract

V. The hemicelluloses were fractionated by successive precipitation of the caustic soda solution with acetic acid; half a volume of acetone; and 1 volume of acetone; the 3 fractions being designated A, B and C. Further subdivision is possible by addition of Fehling''s solution, the fractions insoluble in the reagent being designated A1, B1, and C1, those soluble being A2, B2 and C2. These designations indicate not individual classes of hemicelluloses but methods of preparation. There is an optimum pH for precipitation of fraction A, and low yields of this fraction are obtained if this pH is not reached, the residue of A appearing together with B or C. Improved yields of the fractions may be anticipated if the copper precipitation is carried out with glycerol-cupric sulphate mixtures instead of Fehling''s solution, the copper gel being decomposed with acetic acid instead of HC1.[long dash]VI. The hops are exhaustively extracted with organic solvents to remove resins, pigments, etc.; lignin and pectin are removed and the caustic soda extracts fractionated by successive treatment with acetic acid, half a volume of acetone and one volume of acetone. In this way 4 fractions, A1, B1, B2 and C2, were obtained. Due care was taken to precipitate A1 at optimum pH and glycerol-cupric sulphate mixtures were used for the Cu precipitation. All fractions, of which A1 and B2 were preponderant, consisted of an-hydroxylose, anhydroglucose and glycuronic anhydride in differing proportions. The hop hemicelluloses thus belong to the xylan class usually found in lingnified tissues.