Optimization of enzyme-assisted lipid extraction from Nannochloropsis microalgae

Cell wall disruption is one of the most critical and energy-consuming steps in the overall process of lipid extraction from microalgae. In this paper we investigate a multi-enzyme pretreatment based on the use of cellulase (CEL) and mannanase (GMA) for the recovery of lipids from the marine microalga Nannochloropsis sp. A central composite design coupled with response surface methodology was used to optimize the treatment and evaluate the effect of temperature (T = 15–75 °C), pH (2–8), pretreatment time (P = 30–270 min), CEL dosage (D1 = 0–20 mg/g) and GMA dosage (D2 = 0–2 mg/g) on lipid extraction. About 90% of lipids were recovered from Nannochloropsis cells pretreated under optimal process conditions (T = 53 °C, pH = 4.4, P = 210 min, D1 = 13.8 mg/g and D1 = 1.5 mg/g). FTIR spectra and TEM images of Nannochloropsis cells showed that the enzymatic treatment produced significant alterations in the algal cell wall structure, with extensive loss of cell boundaries and release of intracellular material. Overall, the results obtained indicate that the proposed approach can significantly improve the recovery of lipids from Nannochloropsis sp., further supporting the use of enzymes in microalgal processes.