Defatted Nannochloropsis oculata biomass – Waste or resource?

Microalgae are recognized as a valuable source of a panoply of compounds. In addition to the extensively investigated lipid fraction comprising polyunsaturated fatty acids (PUFA), microalgae biomass also encompasses other compounds with potentially relevant biological activities. This work innovatively repurposes the defatted biomass (DB) of Nannochloropsis oculata, highlighting its potential value beyond the lipid fraction. By subjecting the DB to enzymatic hydrolysis, we explored an underutilized resource, potentially reducing waste and promoting sustainable bioprocessing. The resulting soluble fraction was chemically characterized and a comprehensive assessment of its chemical and biological activities was performed to ascertain its potential applications. Those included antioxidant, anti-hypertensive, and antidiabetic capacities, as well as potential metabolic inhibition, anti-inflammatory, and antimicrobial activities. The chemical characterization revealed the presence of several low molecular weight peptides (<1.2 kDa), as well as polysaccharides. The DB exhibited a relevant antioxidant capacity of 3.15 μmol_{Trolox equivalent(TE)}/mg_{freeze-dried biomass(FDB)} and an IC₅₀ of 77.3 ± 0.3 μg_protein/mL concerning angiotensin-I converting enzyme inhibitory activity, while α-glucosidase activity was inhibited by 19.4 %. Biological activities revealed no relevant inhibition of metabolic activity, an immunosuppression potential and anti-inflammatory activity (decreased expression of all pro-inflammatory cytokines in lipopolysaccharide (LPS)-induced inflammation) was also observed. Moreover, significant antimicrobial activity was observed, particularly against Gram-positive bacteria. These results underscored the potential of the DB to be utilized within a biorefinery concept, thereby transforming it into a resource (co-product) rather than considering it as waste. This study is groundbreaking due to its integrative approach, being the first to report the potential bioactivities of non-lipid extracts from N. oculata cultivated under modulated stress conditions.