Se-enrichment of Chlorella vulgaris grown under different trophic states for food supplementation

Most European countries, including Portugal, have soils with low selenium (Se) concentrations. This mineral has antioxidant and chemoprotective functions essential for the human immune system. Despite Se being mostly supplied in the diet in the inorganic form, organic Se is more rapidly assimilated by the organism, presenting lower toxicity. Microalgae can incorporate inorganic Se and metabolize it into less toxic organic forms. In this context, Chlorella vulgaris biomass was tested as a biological carrier for organic Se. For this purpose, C. vulgaris was cultivated under two trophic regimes (auto-and heterotrophic) supplied with sodium selenate. The optimal Na2SeO4 concentration for autotrophic cultivation was 20 mg.L-1. From the total Se absorbed by the biomass, 81 % was organic. The biochemical composition of Se-enriched biomass compared with the non-supplemented was similar (41 vs 42 % proteins, and 5.3 vs 6.2 % lipids, respectively), except for carbohydrates (0.64 vs 2.6 %, respectively). C18:1 and C18:0 were the major fatty acids present, but different profiles were observed. The same was observed for monosaccharides, being glucose the main monosaccharide. Pigments (Chl a, Chl b, and total carotenoids) were similar for both conditions. All potential toxic metals were below the limits regulated by the European Union. Under the optimal Se concentration for autotrophic C. vulgaris growth, most Se was converted into an organic form and 0.72 g biomass would be enough to satisfy human daily Se requirements. C. vulgaris showed a high potential to be used as a biofortified food to correct or prevent Se deficiency-related diseases.