Effect of ultrasound disruption on lipid extraction from Nannochloropsis sp.

Abstract

Photoautotrophic microalgae are a novel source of biomass rich in lipids containing nutritionally interesting n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA). However, microalgae incorporated into foods as whole biomass may lead to limited n-3 LC-PUFA uptake by the human body. Incorporation of microalgal oil instead of whole biomass is an interesting alternative. The extraction efficiency of these lipids can be enhanced by adding a cell disruption step during lipid extraction. Ultrasound assisted extraction (UAE) to enhance lipid recovery from microalgae has been covered in recent literature. UAE is used to speed up lipid extraction for analytical purposes or for industrially applicable lipid extraction of microalgae. In addition, the ultrasonication and lipid extraction by organic solvents of microalgal biomass has been performed in different set-ups: simultaneous ultrasonication and lipid extraction or ultrasonication and subsequent lipid extraction, ultrasonication of wet biomass or dry biomass. Often, no reference method is included to which the lipid extraction efficiency using UAE is compared and the total lipid content of the biomass is not always specified making it impossible to calculate the extraction efficiency. 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. biomass on the lipid extraction efficiency and the lipid quality, expressed as free fatty acid content and peroxide value. The effect of UAE on wet and dry biomass in the absence or presence of organic solvents is compared. The effect of the solvent system, ultrasonication power and ultrasonication time is studied.The results show that the lipid extraction efficiency increases after UAE. The presence of some solvent systems leads to higher lipid extraction efficiency when UAE is performed on dry biomass compared to wet biomass while for other solvent systems, this is reversed.