Biorefinery Approach from Nannochloropsis oceanica CCALA 978: Neutral Lipid and Carotenoid Co-Production Under Nitrate or Phosphate Deprivation

Abstract

The large-scale culture of microalgae has become a focus of interest for the biorefinery industry, combining the production of biofuels with that of other value-added bioproducts and thus increasing the profitability of the process. In order to evaluate its potential as biodiesel feedstock under a biorefinery approach, the biomass, pigment, nutrient, total lipid and lipid fraction kinetics of the Argentinian Nannochloropsis oceanica CCALA 978 strain were analysed. The species was first cultivated under optimal conditions (f/2 medium) and then transferred to nutritional stress conditions (N-deprivation or P-deprivation media). Under complete f/2 medium, N. oceanica presented maximum growth rate (μ) and chlorophyll-a values and minimum values for lipid and carotenoid content. The high nutrient consumption rate (N or P) in this exponential phase was associated with increasing cell density. Under both nitrate and phosphate deprivation, μ was drastically reduced but biomass production reached its highest values, indicating a phase of metabolite accumulation. Maximum values of total lipids (ca. 39% dw) and carotenoids (1100 × 10−3 ± 15 μg mL−1) were obtained under nitrate deprivation. In addition, total lipid composition was characterized by 92% neutral lipids, 0.7% phospholipids, a high percentage of C16:1 (ca. 37% of total fatty acids) and minimum values of PUFA (5.9% of total fatty acids). Biodiesel properties inferred from the fatty acid methyl ester profile of neutral lipids meet the standards established by EN 14214 and ASTMD 6751-08. Although N and P deficiency both produced an increase in neutral lipids in the studied strain, under a biorefinery approach, nitrate deprivation is considered to be a better method of stress induction than phosphate deprivation for the purpose of co-producing neutral lipids for biodiesel and value-added pigments.