Critical review of the criterion of polysaccharide purity

Natural polysaccharides attract scientists and industries' interest with diverse applications in biomaterials, immune regulation, gut microbiota regulation, food additives, and more. Nevertheless, the absence of standardized purity criteria created significant challenges in characterizing polysaccharides, leading to varied and complicated structures, and impeding progress in research and development. Consequently, it is essential to obtain samples that adhere to high-level and unified purity standards for effective polysaccharide research. Herein we review current methods for assessing polysaccharide purity, emphasizing a commonly neglected impurity: mixtures of polysaccharides with similar molecular sizes. Such a mixture, previously regarded as a single sample, can present a much more complex and ambiguous chemical structure. To address this challenge, we propose enhancing the purity criteria to identify these mixtures. Briefly, the molecular size changes are monitored following hydrolysis with diagnostic enzymes which are identified through methylation and monosaccharide analysis. A pure polymer will exhibit a complete shift in its HPGPC peak, while a polymer mixture will display residual peaks. Establishing standardized criteria for assessing polysaccharide quality represents a significant milestone in the industrialization of these important biomolecules. By enabling accurate, consistent, reliable characterization, this advancement lays the groundwork for broader polysaccharide applications in pharmaceuticals, food, materials, and beyond.