High-value compounds in three freshwater green microalgae using nitrogen as an abiotic stressor: A study of the antioxidant potential of ethanolic extracts

Microalgae are a rich source of several biomolecules, some of which are recognized for their potential antioxidant activity. In this study, Chromochloris zofingiensis , Koliella longiseta , Schizomeris leibleinii were cultivated in five different media, using NaNO 3 or urea as the nitrogen source in different concentrations. BBM STD (BBM standard), BBM (−) - NaNO 3 concentration reduced tenfold, BBM (X) - absence of nitrogen, BBM (U) - urea replacing NaNO 3 in nitrogen equivalent, and BBM (U-) - urea concentration reduced tenfold. The microalgae extracts were analysed for their production of carotenoids, chlorophylls, lipids, and phenolic compounds. In addition, antioxidant activity was assessed using three different assays (DPPH• RSA, FICA, and TAC). K. longiseta showed highest carotenoids (3.8 mg·g −1 ) and chlorophyll (10.8 mg·g - 1 ) content in BBM STD (BBM standard). Indeed, the lower nitrogen supply (ten times less than BBM STD ) induced lipid accumulation, reaching a maximum of 45.1 % in C. zofingiensis (BBM (−), less NaNO 3 ). In contrast, urea (BBM (U), BBM using urea as nitrogen source) enhanced the phenolic contents, achieving 33.2 and 30.8 mg GAE·g −1 , in K. longiseta and S. leibleinii , respectively. Highest antioxidant potential was found in C. zofigiensis (43.1 % RSA, 21.7 % FICA, and 214.6 mg GAE·g −1 TAC) and S. leibleinii (27.7 % RSA, 28.8 % FICA, and 253.4 mg GAE·g −1 TAC). Overall, phenolic compounds seemed to have major contribution to the antioxidant activity than pigments and lipids. • Biomass accumulation or productivity was not improved with urea as the nitrogen source. • K. longiseta showed highest carotenoids (3.8 mg·g −1 ) content in standard BBM. • Highest lipid content (up to 45.1 %) in C. zofingiensis , using tenfold less nitrogen • K. longiseta and S. leibleinii reached higher phenolic content under urea cultivation. • C. zofingiensis and S. leibleinii showed the most promising antioxidant potential.