Solubility of extracted proteins from Chlorella sorokiniana, Phaeodactylum tricornutum, and Nannochloropsis oceanica: Impact of pH-value

Microalgae are a new source of proteins, with yet unknown technofunctionalities. The aim of this work was to study protein solubility - a key technofunctionality - in water in the pH-range of 2-12 of proteins from water-soluble (WSPE) and water-insoluble protein extracts (WISPE) obtained from Chlorella sorokiniana, Phaeodacodum tricomutum, and Nannochloropsis oceanica. Proteins in the WSPEs exhibited an unusual solubility pattern with a solubility >= 39.5 g/100 mL and no complete precipitation in the pH-range 2-12, which was attributed to protein glycosylation and a high amount of hydrophilic amino acids. However, slight aggregation was evident at all pH-values and no transparent solutions were formed. The highest protein solubility was observed for proteins of Nannochloropsis oceanica, followed by Chlorella sorokiniana, and Phaeodactylunz tricornutum. In the WISPEs, strong aggregation and a low solubility ( <= 22.6 g/100 mL) were observed in the pH-range of 2-11, with an increase at pH 12. Overall, the studied proteins exhibited solubility patterns in the pH-range 2-12 that were different to conventional food proteins, and especially the proteins in the WSPE of Nannochloropsis oceanica exhibited a high solubility( >= 58.8 g/100 mL) at pH <= 5. Thus, this fraction is quite promising for food applications (e.g. protein-rich acidic beverages) and is of interest for further studies.