Optimized extraction of neutral carbohydrates, crude lipids and photosynthetic pigments from the wet biomass of the microalga Scenedesmus obliquus BR003

Abstract

The establishment of microalgae as a sustainable source of bioproducts requires a detailed evaluation of unit operations that compose a biorefinery. Biorefining of microalgal biomass is performed in sequence for obtaining a diversity of valuable compounds, but the optimum sequence of biorefining still under scrutiny. Herein, detailed modeling of unit operations was performed to enhance the extraction of neutral carbohydrates, crude lipids, and photosynthetic pigments from the wet biomass (slurry) of the microalga Scenedesmus obliquus BR003. Concentrated sulfuric acid hydrolysis resulted in an optimized extraction yield of 93% at temperature of 80 °C, 1.5 mol L−1 of sulfuric acid solution, and retention time of 120 s. Temperature and retention time were important parameters to increase the extraction of neutral carbohydrates using concentrated sulfuric acid. The efficiency of the multistage extraction of crude lipids was drastically decreased by high biomass-to-solvent ratios, and the use of proper mixing systems and longer mixing times increased the efficiency of this unit operation. The highest lipid content was achieved using orbital shaker (210.1 ± 10.9 mg g−1), retention time of 55 min, and biomass-to-solid ratio of 6.6% (w w−1). The extraction of chlorophylls a and b, and total carotenoids could be described by sigmoidal functions between the extraction yields and ratios of ethanol to the microalgal slurry, hence high levels of ethanol were required to efficiently extract them. The minimum ratio of ethanol to microalgae slurry necessary to efficiently extract photosynthetic pigments from the slurry of S. obliquus BR003 was 0.8:0.2 in volume, and this condition allowed the extraction resulted in extraction yields from 84 to 100%.