Microalgae are rich in several nutritional and health-beneficial components, showing great potential as functional food ingredients. To this extent, knowledge of the biomass composition is essential in the selection of suitable microalgae species for specific food applications. Surprisingly, although cell wall polysaccharides are generally reported to play a role in functionality, limited attention has been given to the cell wall related polysaccharides of microalgae so far. Therefore, this study aimed to characterize dry biomasses of ten microalgae species with potential as functional food ingredients, with a particular focus on the composition of cell wall related polysaccharides. The investigated species were Arthrospira platensis, Chlorella vulgaris, Diacronema lutheri, Tisochrysis lutea, Nannochloropsis sp., Odontella aurita, Phaeodactylum tricornutum, Porphyridium cruentum, Schizochytrium sp. and Tetraselmis chuii. Lipids, proteins and ash made up a large fraction of the biomasses, except for the freshwater algae C. vulgaris and A. platensis which were mainly composed of proteins and polysaccharides. Generally, low amounts of storage polysaccharides (2-8%) were observed in the investigated microalgae species, while extracellular polymeric substances were only present in P. cruentum, O. aurita, C. vulgaris and A. platensis. Cell wall polysaccharides contributed approximately 10% of the biomass and were composed of heteropolysaccharides, showing at least five different monosaccharides. Moreover, the presence of uronic acids and sulfate groups provides anionic characteristics to the cell wall related polysaccharides of several microalgae. As a result, these polysaccharides show potential to display interesting functionalities as bioactive or technological substances.

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Microalgae show great potential for use as novel ingredients in food products, as they are rich in several nutritional and health-beneficial components. However, addition of total microalgal biomass might alter the structural properties of the food system. Therefore, information is required about their rheological characteristics towards selection of microalgae species for specific food products. This study comprises the rheological characterization of seven commercially available microalgae species in aqueous suspensions, before and after mechanical and thermal processing. Substantial differences in rheological properties were observed between the investigated microalgal suspensions. Among the untreated suspensions, Porphyridium cruentum, Chlorella vulgaris and Odontella aurita showed the largest structural properties and could be described as weak gels. All suspensions showed shear-thinning flow behavior at the examined concentration of 8% w/w, except for Nannochloropsis species. Shear-thinning behavior was also observed for the separated serum phase of P. cruentum, which might be attributed to the presence of sulfated exopolysaccharides. During processing, rheological properties were significantly altered. High pressure homogenization was used as a mechanical treatment, followed by a pasteurization or sterilization process. Whereas suspensions of Arthrospira platensis and C. vulgaris showed an increased storage modulus and viscosity after processing, the opposite was observed for P. cruentum and O. aurita. No clear effect of processing was observed for suspensions of Nannochloropsis sp., Schizochytrium sp. and Phaeodactylum tricornutum. Investigation of the microstructure revealed differences in degree of cell disruption by high pressure homogenization, with Nannochloropsis sp. being the most resistant. Subsequent thermal processing resulted in aggregation of released cell material and/or intact cells. In conclusion, the obtained results provide the scientific knowledge base for the selection of microalgae species towards food applications. Whereas some microalgae species hardly affect the structural properties of the food product, other microalgae species show large potential for use as a structuring agent in food applications.

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