Abstract: Oleaginous photoautotrophic microalgae are a novel source of biomass rich in lipids containing nutritionally interesting n-3 long-chain polyunsaturated fatty acids and pigments. However, several microalgae have rigid cell walls acting as barriers to lipid extraction. The cell wall can be disrupted to improve lipid extraction or to increase the bio-accessibility of microalgal lipids. Ultrasound assisted extraction (UAE) to enhance lipid recovery from microalgae has been covered in recent literature. It has been performed in different set-ups while often no reference method is included to which the lipid extraction efficiency using UAE is compared. The total lipid content of the biomass is not always specified making it impossible to calculate the extraction efficiency. In addition, the ultrasound disruption could influence important lipid quality parameters such as the primary oxidation and antioxidant (pigment) content which need to be elucidated before such microalgal lipids can be introduced into the market. Therefore, the effectiveness of this cell disruption technique for industrial microalgae processing has not consistently been proven in literature.
This study investigates the effect of UAE of Nannochloropsis sp. on the lipid extraction efficiency and the lipid quality, expressed as free fatty acid content, peroxide value and pigment composition and content. The effect of UAE on wet biomass in presence of organic solvents is compared to control extractions at room temperature and elevated temperatures mimicking the temperature profiles observed during UAE. The effect of ultrasonication power and time is studied.
The results showed that the lipid extraction efficiency increased after UAE when ultrasound was applied at high power. Control extractions at elevated temperatures resulted in similar lipid extraction efficiencies as observed after UAE. Lipid quality indicators (FFA, peroxide value and pigment composition) varied depending on treatment, treatment duration and power input.
This study is funded by Flanders’ Food and VLAIO (Grant number HBC.2019.0012)
