Study of Schiff base formation between dialdehyde cellulose and proteins, and its application for the deproteinization of crude polysaccharide extracts

Dialdehyde cellulose (DAC) was produced by the selective oxidation of pulp fibers, and was used to bind bovine serum albumin (BSA) by forming Schiff bases. The best binding conditions were as follows: a content of DAC aldehyde groups of 5.15 ± 0.13 mmol/g, a reaction time of 4 h, a reaction temperature of 40 °C, an initial medium pH of 8.0, and a DAC/BSA ratio of 1:50 (g/mL). After the binding of BSA, the FT-IR intensity of the characteristic absorption band (CO) of DAC was weakened, which indicated the formation of imine linkages. The Schiff bases formed between DAC and BSA gave the resulting material a higher thermal stability than that of DAC, and the slender fibers were twisted out of shape. Based on this Schiff base reaction, three different crude polysaccharide solutions (CPSs) were treated with DAC to deproteinize them under best bonding conditions. The results revealed that the DAC method had a higher deproteinization efficiency and polysaccharide recovery than the classical Sevag method. Therefore, the DAC treatment may be an ideal technique for the removal of proteins from CPSs for large-scale purification of polysaccharides.