pH-shift processing of Nannochloropsis oculata microalgal biomass to obtain a protein-enriched food or feed ingredient

Abstract

Keywords:Microalgae Nannochloropsis Food Acid/alkaline solubilization and precipitation Protein n-3 fatty acids 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 debris and precipitating the proteins near their isoelectric point. We here describe the pH-shift process on commercially available Nannochloropsis oculata. The partitioning of major nutrients into the various fractions of the process was studied. 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; both versions were 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. Protein, total fatty acids and carbohydrates were concentrated in the final product, while the ash content was lower compared to the starting material. 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. Owing to its content of protein and (total) fatty acids (23 and 12% of dry weight, respectively), the latter enriched in eicosapentaenoic acid (EPA), the product of the pH-shift process has potential as a functional food ingredient.

Biorefinery of functional biomolecules from algae

“…This can be explained by the elevated cost of the purification processes, which makes it attractive only to high value products for the food, cosmetic and pharmaceutical sector (Eppink et al, 2017). The typical processes reported for algae are ultrafiltration (Safi et al, 2014b;Ursu et al, 2014), pH-shift (Cavonius et al, 2015), aqueous two-phase partitioning (Jordan and Vilter, 1991), chromatography, dialysis (Schwenzfeier et al, 2011), three phase partitioning (Waghmare et al, 2016) and…”

“…In other words, higher yields can be achieved at expenses of low purities. Cavonius et al, (2015) and Ba et al, (2016) reported a process of high pressure homogenization and pH-shifting which resulted in protein yields of 68 to 84 % with purities of 26-44 % (DW). On the contrary, high purities can be obtained by implementing several unit operations, but having as consequence low yields.…”

“…The unit operations commonly applied for the separation and purification of algae biomolecules are isoelectric precipitation (Ba et al, 2016;Benelhadj et al, 2016;Cavonius et al, 2015;Chronakis, 2001;Gerde et al, 2013;Ursu et al, 2014), (ultra)filtration (chapter 4, 7-8, Lorente et al, 2018;Safi et al, 2014b;Ursu et al, 2014), aqueous two-phase partitioning (chapter 6,7, Suarez Ruiz et al, 2018) and sequences of unit operations (Chronakis, 2001;Schwenzfeier et al, 2011;Waghmare et al, 2016).…”

“…Under the presence of a plasticizer, the fractions were able to form stable gels. Isoelectric precipitation was applied to extract proteins from bead milled Nannochloropsis oculata (Cavonius et al, 2015). the extract, containing 23 % proteins and 15 % lipids (dw) was proposed as an interesting functional ingredient for food and feed.…”

“…Precipitation methods take advantage of the solubility and isoelectric point of the target molecules in order to induce selective precipitation. The method is commonly referred as pH-shifting and involves a broad range of pH adjustment to maximize protein solubility followed by precipitation at the isoelectric point (Ba et al, 2016;Benelhadj et al, 2016;Cavonius et al, 2015;Gerde et al, 2013). Filtration methods make use of differences in the polarity and molecular size of the components in suspension to obtain fractions rich in the molecules of interest (Safi et al, 2017(Safi et al, , 2014).…”