Direct enzymatic ethanolysis of potential Nannochloropsis biomass for co-production of sustainable biodiesel and nutraceutical eicosapentaenoic acid

Marine microalga is a promising source for the production of renewable and sustainable biodiesel in replacement of depleting petroleum. Other than biodiesel, is a green and potential resource for the commercial production of nutraceutical eicosapentaenoic acid (EPA, C ). In recent studies, low-value biodiesel can be achieved by transesterification of biomass. However, it is undoubtedly wasteful to produce microalgal biodiesel containing EPA from nutritional and economical aspects. A new strategy was addressed and exploited to produce low-value bulky biodiesel along with EPA enrichment via enzymatic ethanolysis of biomass with a specific lipase. Cellulase pretreatment on sp. biomass significantly improved the biodiesel conversion by direct ethanolysis with five enzymes from (CALA and CALB), (TL), (RM), and (PLA). Among these five biocatalysts, CALA was the best suitable enzyme to yield high biodiesel conversion and effectively enrich EPA. After optimization, the maximum biodiesel conversion (46.53-48.57%) was attained by CALA at 8:1 ethanol/biomass ratio (v/w) in 10-15% water content with 10% lipase weight at 35 °C for 72 h. Meanwhile, EPA (60.81%) was highly enriched in microalgae NPLs (neutral lipids and polar lipids), increasing original EPA levels by 1.51-fold. Moreover, this process was re-evaluated with two species (IMET1 and Salina 537). Under the optimized conditions, the biodiesel conversions of IMET1 and Salina 537 by CALA were 63.41% and 54.33%, respectively. EPA contents of microalgal NPLs were 50.06% for IMET1 and 53.73% for Salina 537. CALA was the potential biocatalyst to discriminate against EPA in the ethanolysis of biomass. The biodiesel conversion and EPA enrich efficiency of CALA were greatly dependent on lipidic class and fatty acid compositions of biomass. CALA-catalyzed ethanolysis with biomass was a promising approach for co-production of low-value biodiesel and high-value microalgae products rich in EPA.