Microalgal biomass as a (multi)functional ingredient in food products: Rheological properties of microalgal suspensions as affected by mechanical and thermal processing

Abstract

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.

Evaluation of the effect of agitation speed on the growth and high‐value LC‐PUFA formation of Porphyridium cruentum based on basic rheological analysis

“…Indeed, EPS in P. cruentum acts as a glue between cells, which improves cell clustering. 46 Therefore, the degree of aggregation of microalgal cells was proportional to EPS concentration -greater EPS concentration gave greater cell aggregation. This conclusion was consistent with study of another red microalga Rhodosorus marinus 47 , where aggregation increased during cultivation with the biomass concentration increase and EPS production.…”

The light/dark cycle of microalgae in a thin-layer photobioreactor

“…A strong interest in cultivation of phototrophic microalgae is driven by their several envisaged application areas: a non-exhaustive list includes biofuels, chemicals, medicine and nutrition (Posten and Walter 2012). Microalgae hold potential in food production and in purification of contaminated water and wastewater (Acién et al 2016;Bernaerts et al 2017). They are important in the food chain as they are the main feeding source for rotifers, fishes, etc.…”

Rheological properties of concentrated slurries of harvested, incubated and ruptured Nannochloropsis sp. cells

“…There have been a number of recent studies of the rheological behaviour of microalgae suspensions [8][9][10][11][12], including a few reporting rheological measurement of 20-25% solids slurries [13][14][15][16][17] (Table 1). This concentration range is practically important for process intensification [4], and of rheological interest due to exponentially increasing viscosity resulting from close packing [18].…”

“…This concentration range is practically important for process intensification [4], and of rheological interest due to exponentially increasing viscosity resulting from close packing [18]. The slurries of various microalgae, including Nannochloropsis, have been found to be shear thinning, with a high-shear viscosity that is highly dependent on solids concentration [9,11,14,15]. In these studies, cells were harvested via centrifugation, without the use of flocculants.…”