Unravelling Rheology and Structural Properties of Polysaccharides from Porphyridium Purpureum After Alkali Pre-Treatment.

In the quest for sustainable biomaterials, polysaccharides from marine organisms caught attention for their unique chemical and bioactive properties. Their functional properties are significantly dependent on the extraction and preparation methods. Reports on the effect of alkali pre-treatment of the microalgal biomass before extraction on the rheology and structural properties of polysaccharides are limited. In this study, polysaccharides were extracted and fractionated after alkaline pre-treatment of the Porphyridium purpureum biomass at different alkali concentrations (0%, 1%, 3%, and 5% w/v). The effects of alkali concentration on the extraction rate, rheology, and other significant microstructural properties were investigated. The results showed that among all tested conditions, 1% alkali pre-treatment provided the most favorable combination of extractability and functional properties retention. It preserved essential structural features, sustained moderate to high viscosity and viscoelasticity, and yielded a polymer population suitable for viscoelastic applications. Higher alkali concentrations (3% and 5%) were found to cause de-esterification and breakage of glycosidic linkages, resulting in lower polysaccharide yields, lower molecular weight, and weaker viscoelastic properties. These findings not only inform the structural-functional relationship of Porphyridium cellular polysaccharides but also highlight their potential as sustainable alternatives to plant/ macroalgal- or synthetic-derived hydrocolloids for industrial applications.