2.4. Microwave-Assisted Extraction (MAE) of Lipids Using ILs and Prodcution of DHA via Transesterification

MAE was employed to extract the total lipid from a microalgae Nannochloropsis sp. biomass at 700 W energy and a frequency of 2.45 GHz. The method was adapted from a previous work [53]. A solution consisting 2% w/v IL and 15 mL distilled water was prepared and used as the extraction medium for 0.5 g dry microalgae biomass (3.3% w/v biomass loading). Using a domestic microwave, the sample was heated to 90 °C for 25 min. Next, methanol and chloroform were added to the solution before it underwent centrifugal phase separation at 6000 rpm for 10 min. The sample formed two separate phases. The chloroform phase was then isolated and washed with a solution of distilled water and hexane, 2 or 3 times, to ensure that any residual polar compounds had been completely removed. Finally, lipids were recovered from the hexane phase through evaporation. In order to synthesize the DHA compounds, transesterification of the extracted lipid was performed. A method of producing fatty acid methyl esters (FAMEs) that contain DHA was adapted from previous literature reports [54,55]. The produced FAMEs were duly separated and sent for analysis via gas chromatography (Agilent 6890 GC, USA) equipped with a flame ionization detector (FID). The schematic sequences of empirical lipid extraction and DHA production are presented in Figure 2. The calculation of DHA follows Equation (7) in terms of percentage recovered (%) and Equation (8) in the terms of amount (mg/g) of FAMEs.

Schematic of experimental setup of lipid and DHA extraction from microalgae biomass.