Screening of rheological properties of various microalgae species towards their application in processed food products

Microalgae are considered a promising source of several health beneficial components and nutrients, including omega-3 polyunsaturated fatty acids, proteins and antioxidants. To date, intensive research is carried out towards extraction of individual components from microalgae. However, using the complete microalgal biomass in food products might be an innovative strategy to combine all health beneficial and nutritional advantages. In addition, this strategy provides the ability to use other functional components from microalgae. Cell wall related polysaccharides could for instance play a structuring role in food products, allowing microalgal biomass to be used as a multifunctional ingredient. In this context, fundamental knowledge is required on the rheological properties of microalgae, which are only very limitedly described in literature. In addition, the rheological behavior might be altered by mechanical and thermal processing, treatments that are commonly used in food processing. Mechanical processing is often applied for functionalization of food products, such as tailoring rheological properties of vegetable based products. In contrast, thermal processing is a conventional preservation technique to create shelf-stable food products. To the best of our knowledge, no reports were found about the effect of mechanical and thermal processing on the rheological properties of microalgal suspensions. Therefore, this study comprises a screening of the rheological characteristics of different microalgae species (Chlorella, Nannochloropsis, Odontella, Phaeodactylum, Porphyridium, Schizochytrium and Spirulina) and their change upon mechanical and thermal processing. Microalgal biomasses were commercially obtained as dry powder. Aqueous model systems were prepared at both pH 4 and 6, simulating fruit and vegetable based products respectively. These suspensions were then mechanically treated, using high pressure homogenization at 100 MPa. Subsequently, thermal processing was applied, using a pasteurization or sterilization process for suspensions at pH 4 and 6, respectively. The effect of processing was investigated both on rheological properties and microstructure of the microalgal suspensions. The obtained results showed substantial differences in rheological properties between the different microalgae species. The impact of mechanical processing was largely depending on the type of microalga, while thermal processing mostly resulted in structure build-up. Changes in flow behavior after processing could be related to both particle characteristics and serum viscosity. The results of this study show the great potential of microalgal biomass towards food applications. Whereas some microalgae species can be used to introduce health beneficial components without disturbing the structure of the food matrix, other species displayed interesting thickening properties for use as a multifunctional ingredient in food products.status: publishe