Analysis of the lipid extraction performance in a cascade process for Scenedesmus almeriensis biorefinery

Abstract

Background Microalgae have attracted considerable interest due to their ability to produce a wide range of valuable compounds. Pulsed Electric Fields (PEF) has been demonstrated to effectively disrupt the microalgae cells and facilitate intracellular extraction. To increase the commercial viability of microalgae, the entire biomass should be exploited with different products extracted and valorized according to the biorefinery scheme. However, demonstrations of multiple component extraction in series are very limited in literature. This study aimed to develop an effective lipid extraction protocol from wet Scenedesmus almeriensis after PEF-treatment with 1.5 MJ·kgDW−1. A cascade process, i.e., the valorization of several products in row, was tested with firstly the collection of the released carbohydrates in the water fraction, then protein enzymatic hydrolysis and finally lipid extraction. Biomass processed with high pressure homogenization (HPH) on parallel, served as benchmark. Results Lipid extraction with ethanol:hexane (1:0.41 vol/vol) offered the highest yields from the different protocols tested. PEF-treatment promoted extraction with almost 70% of total lipids extracted against 43% from untreated biomass. An incubation step after PEF-treatment, further improved the yields, up to 83% of total lipids. Increasing the solvent volume by factor 2 offered no improvement. In comparison, extraction with two other systems utilizing only ethanol at room temperature or elevated at 60 °C were ineffective with less than 30% of total lipids extracted. Regarding cascade extraction, carbohydrate release after PEF was detected albeit in low concentrations. PEF-treated samples displayed slightly better kinetics during the enzymatic protein hydrolysis compared to untreated or HPH-treated biomass. The yields from a subsequent lipid extraction were not affected after PEF but were significantly increased for untreated samples (66% of total lipids), while HPH displayed the lowest yields (~ 49% of total lipids). Conclusions PEF-treatment successfully promoted lipid extraction from S. almeriensis but only in combination with a polar:neutral co-solvent (ethanol:hexane). After enzymatic protein hydrolysis in cascade processing; however, untreated biomass displayed equal lipid yields due to the disruptive effect of the proteolytic enzymes. Therefore, the positive impact of PEF in this scheme is limited on the improved reaction kinetics exhibited during the enzymatic hydrolysis step.

Application of Pulsed Electric Fields and High-Pressure Homogenization in Biorefinery Cascade of C. vulgaris Microalgae

“…Figure 5c shows the yield of recovered lipids from the untreated samples, and those subjected to PEF alone, HPH alone, and cascade treatments. The electroporation of cell membranes caused a significant (p ≤ 0.05) increase in the extraction yield of lipids in comparison with controls, in agreement with previously published papers reporting that the enhancement of lipids extraction by PEF is effective [10,20,40,48,54]. For instance, in the work of Lai et al [54], the application of a PEF treatment of constant intensity (30.6 kWh/m 3 ) on Scenedesmus biosuspensions yielded 3.1-fold more crude lipids and fatty acid methyl esters (FAME) than those from conventional solvent extraction.…”

“…enhancement of lipids extraction by PEF is effective [10,20,40,48,54]. For instance, in the work of Lai et al [54], the application of a PEF treatment of constant intensity (30.6 kWh/m 3 ) on Scenedesmus biosuspensions yielded 3.1-fold more crude lipids and fatty acid methyl esters (FAME) than those from conventional solvent extraction.…”

“…Because of the different properties of the intracellular molecules found in microalgae, whose mass distribution greatly depends on the considered species, as well as on applied cultivation conditions [16,17], microalgae processing can be suitably carried out through a wet-route "biorefinery" scheme, to obtain different classes of compounds upon a multi-Foods 2022, 11, 471 2 of 16 stage downstream processing phase, involving mild and economically feasible separation steps [18][19][20][21][22].…”

“…Therefore, a progressive permeabilization strategy, which can be tailored for each specific strain, has emerged as the cornerstone front of the full valorization of microalgal biomass through an efficient and sustainable biorefinery process [5,20,24,25].…”

“…Despite several authors having reported examples of microalgal processing for the recovery of value-added compounds, based either on PEF alone or its combination with mechanical treatments [6,20,[36][37][38][39], to the best of our knowledge, this is the first attempt to develop an entire microalgal biorefinery scheme, integrating PEF and HPH technologies with different post-processing methods, to pursue the complete valorization of microalgal biomass through enhanced selectivity and yield of extraction (Figure 1).…”