Nannochloropsis oceanica: a source of bioactive peptides

Nannochloropsis oceanica, a marine microalgae, represents a source of protein and important fatty acids, such as eicosapentaenoic acid (EPA), making it interesting for application in human food or animal feed. Proteins hydrolysis of this microalga can provide added value through the release of bioactive peptides with several potential biological properties, namely antioxidant, anti-hypertensive, anti-inflammatory and anticancer activities. Nannochloropsis oceanica has a rigid and hard to break wall, thus hydrolysates could increase the bioavailability of proteins and the release of bioactive peptides and EPA, conveying new economic value for the industry. This work aimed to obtain a soluble microalga extract rich in bioactive peptides, through an optimized enzymatic hydrolysis, instead of mechanical methods, as they may be more feasible and affordable for industrial applications. Nannochloropsis was submitted to several extraction conditions, with variable factors including temperature, incubation time, enzyme type and concentration. To achieve the optimal extraction conditions, a Box-Behnken experimental design was performed using statgraphic centurion software. Factorial design allowed an evaluation of the effects of four factors (cellulose and protease concentration, temperature and hydrolysis time) on protein release, hydrolysis degree and extracts bioactivities. The protein content of each extract was determined by kjeldahl and hydrolysis degree by 2,4,6-trinitrobenzene-l-Sulfonic acid method. The antioxidant activity of the peptides was tested by oxygen-radical absorbance-capacity (ORAC) assay and total phenolic content was estimated by folin ciocalteu method.A combination of a cellulase and a protease appeared to be the best method to achieve the highest protein and bioactive peptide extraction. The best extracts showed 32% of soluble protein/dry weight and an antioxidant activity of 31 μmol Trolox Equivalent/mL extract. The concentration of cellulase used was the major factor for protein release.Thus, the factorial design allowed to confirm the combination of experimental factors that leads to the most efficient extraction of antioxidant peptides, validating the studied extraction method.The resulting soluble extract can be applied in food, cosmetic and animal feeding and the insoluble extract can be used for the enrichment of animal feed.