pH-shift processing of Nannochloropsis oculata microalgal biomass to obtain a protein-enriched food or feed ingredient
Conference contribution, 2015
lthough some species of microalgae have potential as human and animal nutrition due to the presence of high-value protein and polyunsaturated fatty acids, there has been relatively little development of algal food products. Fractionation of plant and animal raw materials by pH-shift processing has been widely applied to purify proteins. The principle is to solubilize proteins at high or low pH, removing insoluble material and precipitating the proteins near or at their isoelectric point. We have applied the pH-shift process to the commercially-available, marine microalga Nannochloropsis oculata and studied the partitioning of major nutrients into the various fractions emerging from the process. The process was developed and adapted to the biomass with scalability in mind. Proteins were found to exhibit maximal solubility between pH 7 and 10, with a minimal solubility below pH 4. Two process versions were investigated in this study, with solubilization at either pH 7 (native pH) or 10; in both versions, proteins were efficiently precipitated at pH 3. Up to 85 % of both the protein and total fatty acids were recovered in the final product, compared to the initial algal slurry. The amino acid profile was not altered by the process, apart from a minor increase in phenylalanine, counteracted by a minor decrease in proline. From a processing point of view, solubilization of Nannochloropsis at native pH was found to be preferable, since less chemicals were consumed compared to high-pH solubilization. The final product was on a dry-weight basis 23 % protein (of which 43 % were essential amino acids), 12 % total fatty acids (of which 18 % were eicosapentaenoic acid), 37 % carbohydrates and 34 % ash, and thus has potential as a functional food ingredient.