Structural characterization of exopolysaccharides obtained from Porphyridium cruentum exhausted culture medium

Microalgae produce and secrete large quantities of polysaccharides into the culture medium that is discarded when biomass is separated. The main objective of this study was to add value to the exhausted culture medium (ECM) of Porphyridium cruentum through the recovery of extracellular polysaccharides (EPS) by different extracting and purifying methods for the future biotechnological applications. The ECM was submitted to pre-cipitation with cold absolute ethanol, using ultrasound, dialysis, and trichloroacetic acid (TCA) as purification methods. The purification provided a lower yield, with higher car-bohydrate content. The TCA purified sample presented up to twice as much total carbo-hydrates as the non-purified samples, mainly composed of xylose, galactose, and glucose. Scanning Electron Microscopy (SEM) images showed the smooth structure of P. cruentum EPS, in which TCA post-treatment and dialysis allowed obtaining larger and purest par-ticles, being a good candidate for film making. Microalgal polymeric by-products are a sustainable source to recover valuable compounds, and the purification treatment proved to be an important step to valorize this material.(c) 2023 The Authors. Published by Elsevier Ltd on behalf of Institution of Chemical Engineers. This is an open access article under the CC BY-NC-ND license (http://creati-vecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

The study aimed to recover extracellular polysaccharides (EPS) from the exhausted culture medium (ECM) of Porphyridium cruentum using different extracting and purifying methods for future biotechnological applications. The purification methods, including precipitation with cold absolute ethanol, ultrasound, dialysis, and trichloroacetic acid (TCA), resulted in lower yield but higher carbohydrate content. TCA purification provided twice as much total carbohydrates as the non-purified samples, mainly composed of xylose, galactose, and glucose. Scanning Electron Microscopy (SEM) images revealed the smooth structure of P. cruentum EPS, with TCA post-treatment and dialysis yielding larger and purest particles suitable for film making. Microalgal polymeric by-products are a sustainable source of valuable compounds, and purification treatment is an important step in valorizing this material.