Surfactants and Temperature Steer Which Microalgal Compounds End Up in Extracts

Microalgae are packed with valuable molecules, but getting them out of the cell is notoriously difficult. A new open-access study in Discover Energy reports that adding surfactants to ethanol-based extraction of Chlorella vulgaris, combined with microwave-assisted extraction (MAE) or pressurized liquid extraction (PLE), changes not only how much material is recovered but also which compounds end up in the extract. The work, led by Gina Lorena Gonzalez Hurtado and colleagues in Brazil, tested the cationic surfactant CTAB, the anionic SDS, and the non-ionic Triton X-100, and found that surfactant effects were strongly dependent on the extraction technology and, in the case of PLE, on temperature.

The researchers first characterized the raw material, a commercially obtained C. vulgaris powder, and found a protein content above 55%, roughly 29% carbohydrates by difference, and pigments dominated by chlorophyll a. They then compared three extraction routes. Conventional Soxhlet extraction with ethanol delivered the highest overall yield, 14.415%, while hexane yielded only 5.731%. The trade-off was selectivity: ethanol extracts showed higher antioxidant activity in both DPPH and ABTS assays and higher total phenolic content, whereas hexane extracts contained more carotenoids and chlorophyll a and a broader fatty acid profile, including polyunsaturated fatty acids such as palmitoleic and linoleic acids.

Microwave-assisted extraction offered a striking time advantage. Kinetic modeling with a Piecewise 3 function showed a constant extraction rate stage up to about 2.5 minutes and a plateau reached after roughly 15 minutes, so the team ran MAE at 80 °C for just 15 minutes. Under these conditions, MAE with pure ethanol achieved a yield of 11.87% — lower than Soxhlet’s 14.41% but obtained in a fraction of the 4.5-hour Soxhlet run time — and produced extracts with high antioxidant activity, particularly in the ABTS assay, together with chlorophyll and carotenoid contents that fell between the values seen for ethanol and hexane Soxhlet extracts.

Surfactants, however, had limited influence under the MAE conditions. Across concentrations of 0.05 to 0.5 grams per liter, none of the three surfactants produced a clear concentration-dependent trend in yield, and only Triton X-100 at 0.1 grams per liter differed significantly from the pure ethanol control. That condition actually lowered the extraction yield along with total phenolic content, antioxidant activity, and pigment recovery. The authors note that this contrasts with earlier microwave studies in aqueous media, where water’s high dielectric constant dominates heating; with ethanol as the solvent, and given that no prior study has combined MAE of microalgae with surfactants in ethanol, the role of surfactants under these conditions could not be inferred from water-based systems.

Pressurized liquid extraction told a different story. Running PLE with pure ethanol at 80 °C and 10 megapascals, the kinetic model indicated a falling-rate stage continuing to nearly 50 minutes without a fully reached diffusion-controlled plateau, so 60 minutes was chosen for subsequent experiments. In exploratory assays at 0.1 grams per liter, CTAB did not significantly improve yield over pure ethanol and was dropped, while both Triton X-100 and SDS raised extraction yields approximately 1.74-fold compared with the control, with no significant difference between the two. Triton X-100 was selected for detailed study because of its liquid state, stability, and comparatively low toxicity.

Temperature proved decisive. Contrary to the usual expectation that higher temperatures improve PLE efficiency, extraction yields were higher at 40 °C than at 80 °C under both pure ethanol and surfactant-assisted conditions. A two-way analysis of variance showed that yield was significantly affected by both temperature and surfactant presence independently, with surfactant presence exerting the larger influence, while carotenoid content was not significantly affected by any tested parameter. Chlorophyll a and b, by contrast, were significantly influenced by temperature, surfactant presence, and their interaction, indicating that the surfactant’s effect on pigment recovery was temperature-dependent rather than constant.

The pattern of antioxidant responses also shifted with conditions. Under pure ethanol, raising the temperature from 40 to 80 °C reduced extraction yield, total phenolic content, and chlorophyll a recovery, yet increased antioxidant activity in both the DPPH and ABTS assays — a combination the authors interpret as a change in extraction selectivity rather than a simple enhancement of extraction. With Triton X-100 present, the picture differed again: at 40 °C the surfactant increased yield, chlorophyll b recovery, total phenolic content, and ABTS activity while lowering DPPH values, whereas at 80 °C it increased yield and DPPH activity but reduced chlorophyll b and ABTS values. The authors suggest these divergences may reflect the different compound classes detected by each assay, since DPPH is generally more sensitive to hydrophobic antioxidants in organic media while ABTS can detect both hydrophilic and lipophilic species.

Supporting analyses added context rather than dramatic claims. A principal component analysis of the characterization data explained 68.1% of the variance in two components and separated the extracts by profile: hexane Soxhlet extracts aligned with pigment-related variables, MAE ethanol extracts with antioxidant-related responses, and PLE extracts clustered differently depending on temperature and surfactant, with the 40 °C Triton X-100 extract positioned near the ethanol Soxhlet extract. Cryo-transmission electron microscopy of the residual biomass showed differences in aggregation and particle distribution after treatment, but no extensive cell rupture under any condition — consistent with the known rigidity of the C. vulgaris cell wall, which is relatively thick and rich in cellulose and hemicelluloses. Gas chromatography–mass spectrometry showed palmitic acid (C16:0) as the predominant fatty acid in all extracts, with oleic acid (C18:1) prominent in MAE and PLE extracts, while Soxhlet, particularly with hexane, recovered the broadest fatty acid diversity. Surfactant addition had minimal influence on the detectable fatty acid profiles.

The authors are careful to frame the work as exploratory. The biomass was a commercial dried powder rather than laboratory-grown material, extraction conditions differed between techniques so cross-method comparisons are indicative trends rather than direct performance tests, and the GC-MS analysis was qualitative and semi-quantitative. Notably, the surfactant concentrations used were below reported critical micelle concentrations in ethanol, and the authors suggest the surfactant likely remained dispersed as monomers or small aggregates, potentially altering solvent properties within the extraction medium rather than acting through classical micelle formation. Even so, the study demonstrates a concrete principle: by adjusting temperature and surfactant presence in ethanol-based PLE, extractors can steer the compositional and bioactive profile of C. vulgaris extracts under relatively mild conditions, offering a tunable alternative to brute-force yield maximization with greener solvents.

Subject of Research: Surfactant-assisted ethanol extraction of bioactive compounds from Chlorella vulgaris using microwave and pressurized liquid extraction

Article Title: Tuning bioactive compound recovery from Chlorella vulgaris through surfactant-assisted ethanol extraction under microwave and pressurized liquid technologies

Article References: Hurtado, G. L. G., Motta, G. E., Ferreira, S. R. S., & de Andrade, C. J. (2026). Tuning bioactive compound recovery from Chlorella vulgaris through surfactant-assisted ethanol extraction under microwave and pressurized liquid technologies. Discover Energy, 6(1), Article 80. https://doi.org/10.1007/s43937-026-00192-x

Image Credits: AI Generated

DOI: 10.1007/s43937-026-00192-x

Keywords: Chlorella vulgaris, microalgae, surfactant-assisted extraction, pressurized liquid extraction, microwave-assisted extraction, ethanol, Triton X-100, antioxidant activity, chlorophyll, fatty acids, extraction yield, green solvents