Fractionation of polysaccharides by gradient non-solvent precipitation: A review

Almost all natural polysaccharides have wide molecular weight distribution and the complex heterogeneous polysaccharides may also exhibit variations in proportions of sugar constituents, linkage type, degree and arrangement of branching or degree of substitution. The heterogeneity of molecular weight and chemical structure restricts basic research and application of polysaccharides. Therefore, it is meaningful to fractionate polysaccharides into fractions with high homogeneity in molecular weight and chemical structure. Compared with chromatography and ultrafiltration, gradient non-solvent precipitation is inexpensive, has a wide application scope and can be easily scaled up or down as required. Therefore, this work reviews fractionation of polysaccharides by gradient non-solvent precipitation. Specifically, this work describes the commonly used non-solvents, fractionation mechanism of gradient non-solvent precipitation, how to establish the fractionation procedure, assessment of the fractionation effect and factors that affect fractionation. This paper provides comprehensive and detailed directions for how to fractionate a new polysaccharide using this method. It is suggested to select a suitable non-solvent and establish the fractionation procedure according to the curve of the polysaccharide recovery as a function of the non-solvent concentration. Fractionation by gradient non-solvent precipitation is based on the difference in solubility of polysaccharides. Therefore, fractionation may be affected by the precipitation conditions and those factors that can affect the solubility of polysaccharides. During fractionation, those factors that negatively affect fractionation should be strictly controlled.