Microalgae Biomass and Bioactive Compounds Change According to the Medium's N and pH

Abstract

Microalgae have been widely studied as raw materials for biofuels, food supplements and several high value products. The hypothesis is that the pH and N levels in the culture medium are important factors to increase microalgae biomass production and its by-products. Thus, this study aimed to evaluate response of Neochloris oleoabundans to sodium nitrate concentration and pH levels by assessing biomass production, pigments, total lipid content and lipid profile of cells. The experimental design was a complete factorial with two factors: sodium nitrate (NaNO3) using the doses of 0.25, 1.12 and 2.5 g L -1 and pH 5.0, 7.0 and 9.0, resulting in nine treatments and three replicates. Differences in the N concentration and pH of the in Bold's basal medium increased up to 21.1% the production of dry biomass but also up to 36% of lipids and up to of 0.81% of carotenoid concentration in the N. oleoabundans cell. The nuclear magnetic resonance (NMR) analysis of bio-oil showed changes in the lipid profile. Oil extracted from N. oleoabundans cells growing in medium at pH 9 and in 2.5 g L −1 of NaNO3 showed fatty acids with molecular weights similar to crude soybean oil, while the oil from treatment 3 (2.5 NaNO3 g L −1 ) showed a slight increase in molecular weight. Overall, the best adjustment of the liquid medium to grow N. oleoabundans is at pH 9.0 and with addition of 2.5 g of sodium nitrate. HIGHLIGHTS• Variation of N levels and the pH of the medium improves growth of N. oleoabundans.• N is an important factor on the lipid content of N. oleoabundans.• N. oleoabundans produces higher chlorophyll content at pH 9.• N. oleoabundans produces lipids with saponification values similar to soybean oil.• There is interaction of pH and sodium nitrate on the response of N. oleoabundans.