Polyuronans obtained by regiospecific oxidation of polysaccharides from Aspergillus niger, Trichoderma reesei and Saprolegnia sp.

The biomasses of Aspergillus niger, Trichoderma reesei and Saprolegnia sp. were submitted to sodium dodecylsulfate washing, mechanical disruption of the mycelia, stirring at 60°C for 3 h and protracted stirring overnight at room temperature. They were then oxidized regiospecifically at C6 with NaOCl and NaBr for 30 min at room temperature in the presence of Tempo® as a catalyst. The powders obtained were polyuronans in the sodium salt form, fully soluble in water over the pH range 3¯12. Yields were much higher than for the chitosan extraction. The polyuronans were characterized by 1H NMR spectrometry and were shown to contain 20 and >75% 6oxychitin, for A. niger and T. reesei, respectively. The deconvolution of the FTIR spectra in the range 1500¯1800 cm-1 confirmed the presence of a band at 1568 cm-1 that was assigned to chitin amide. This band was seen much more evidently in T. reesei than in the A. niger material. Since the fungi examined are representative of the three major types of cell walls, and are used industrially, it is concluded that the process is simple to follow and is of wide applicability. The process allows upgrading of the spent biomasses and the exploitation of their polysaccharides for industrial applications: examples are given where the polyuronans are reacted with glycerol or with poly (ethyleneglycol) to provide water soluble products with enhanced viscosity.