Structural characterization of exopolysaccharides obtained from Porphyridium cruentum exhausted culture medium

Abstract

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 precipitation with cold absolute ethanol, using ultrasound, dialysis, and trichloroacetic acid (TCA) as purification methods. The purification provided a lower yield, with higher carbohydrate content. The TCA purified sample presented up to twice as much total carbohydrates 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 particles, 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.