Direct extraction of lipids from wet microalgae slurries by super-high hydrostatic pressure

Abstract

Microalgae are undergoing intense study as feedstock to produce biodiesel. However, due to the relatively low price of biodiesel, microalgae have recently been considered a novel source of food and functional products because they contain valuable natural products. Lipid extraction from wet microalgae slurries is considered an energy-saving extraction technique and often includes the use of liquid CO2, switchable solvent, organic solvent, dimethyl ether, and other pre-treatment methods. These methods led to either low extraction efficiencies additional treatment of the residue, or both. Therefore, super-high hydrostatic pressure (100–1000 MPa) is a processing technology mainly applied in the food industry for non-thermal sterilization that could offer several benefits: 1) a super-high pressure can disrupt cells and increase extraction yield; 2) non-thermal treatment will guarantee the extraction of biofunctional products without limited destruction; and 3) a super-high pressure saves energy costs for sterilization and denaturation of the residue, which could be used as a commercial edible protein or animal feed. However, there are no previous reports about lipid extraction by super-high hydrostatic pressure from wet microalgae slurries or regarding considerable challenges. In this study, we investigated two types of extraction from wet microalgae slurries by super-high hydrostatic pressure: one-step extraction and two-step extraction. We also compared the super-high hydrostatic pressure technique with high-pressure homogenization, ultrasonication and microwave extraction by evaluating cell disruption and lipid extraction yields. The highest cell disruption of 92.8 ± 2.7% and lipid extraction yield of 11.4 ± 0.4% were obtained when super-high hydrostatic pressure (SHHP) was applied in the one-step extraction process. In the two-step extraction process, the highest cell disruption of 87.8 ± 2.3% and lipid extraction yield of 10.1 ± 0.7% were obtained by SHHP treatment which was higher than those achieved by the other three treatments with the same wet microalgae slurry. Thus, SHHP can achieve high cell disruption and lipid extraction yields from wet microalgae slurries through the one-step extraction method.