Lore Gheysen

Impact of processing on n-3 LC-PUFA in model systems enriched with microalgae

Microalgae have already shown their potential as an alternative source of n-3 LC-PUFA. In this study, 5 different microalgal species (Isochrysis, Nannochloropsis, Phaeodactylum, Porphyridium and Schizochytrium) were added to an acidic model system and screened on their potential use in acidic food matrices. The impact of mechanical and thermal processing on the model systems was studied by analyzing the amount of n-3 LC-PUFA, free fatty acids, carotenoids, lipid polymers and the oxidative stability. A (limited) reduction of n-3 LC-PUFA was observed. Thermal alterations combined with the presence of free fatty acids seemed to be the causing factor for this decrease. Furthermore, the oxidative stability of model systems enriched with photoautotrophic microalgae was significantly higher than of those enriched with heterotrophic microalgae. It can therefore be concluded that photoautotrophic microalgae low in initial free fatty acid content are a promising source of n-3 LC-PUFA in thermally processed acidic food systems.

Molecular and rheological characterization of different cell wall fractions of Porphyridium cruentum

Cell wall related polysaccharides of the red microalga Porphyridium sp. were shown to be a promising source of new sustainable thickening agents. Isolated extracellular polysaccharides (EPS) consisted of high molecular weight polymers, showing a higher intrinsic viscosity compared to several commercially used hydrocolloids. Aqueous solutions of EPS (2% w/w) were characterized by substantial viscosities and weak gel behavior. Even though the extracted water soluble cell wall polysaccharides exhibited the same monosaccharide profile as EPS (composed of galactose, glucose, xylose and glucuronic acid), a lower molecular weight and intrinsic viscosity was observed for this fraction, resulting in poor rheological properties. Therefore, it was hypothesized that the physicochemical properties were related with a different molecular structural organization of these monosaccharides and sulfate groups. The main challenge for commercialization of extracellular polysaccharides of Porphyridium sp. remains the purification of these fractions to obtain polysaccharide extracts with low protein and salt contents.