Current emerging trends in structure and bioactivities of acidic and alkali-extracted polysaccharides: A review

Acidic and alkali extractions are two fundamental methods for isolating bioactive polysaccharides, each generates distinct molecular structures that critically determine their biological functionalities. Despite the broad utilization of these techniques in producing polysaccharides that exhibit significant therapeutic potential, in-depth and systematic analyses of their extraction mechanisms, structural features, and resulting bioactivities remain insufficiently explored. This comprehensive review provides a critical comparative analysis across four key dimensions: (1) extraction, separation and purification methodologies of polysaccharides, (2) method-induced structural disparities, including molecular weight distribution and monosaccharide composition, (3) bioactivities, such as antioxidant, immunomodulatory, anti-tumor, anti-inflammatory, hypoglycemic, and hypolipidemic effects, (4) structure-function relationship governing polysaccharide bioactivity. The current review highlights that alkali-extracted polysaccharides often exhibit higher molecular weights and enhanced immunomodulatory and anti-tumor properties, whereas acidic-extracted polysaccharides tend to possess lower molecular weights and superior antioxidant activity. Despite extensive research on polysaccharides, a systematic comparison of the emerging trends in structure and bioactivity between acidic- and alkali-extracted variants is lacking. By elucidating these aspects, this review covers relevant literature over the past decade aims to bridge critical gaps in method-structure-function understanding and offer valuable insights to guide the production of high-quality polysaccharides for functional foods and therapeutic agents.