A new approach on astaxanthin extraction via acid hydrolysis of wet Haematococcus pluvialis biomass

Astaxanthin is attracting considerable interest due to its high inhibitory power of oxidative stress in humans and can be produced by the microalga Haematococcus pluvialis. However, the highly physicochemical resistant cell wall of H. pluvialis poses an important challenge in extracting intracellular compounds. We therefore conducted a multiple variable evaluation of acid hydrolysis for cell disruption of wet H. pluvialis biomass, followed by solid-liquid extraction with GRAS (generally recognized as safe) solvents. Preliminary tests selected hydrochloric acid as the most suitable acid for hydrolysis and acetone as the most appropriate solvent for solid-liquid extraction. A central composite design and response surface model were utilized to predict the best conditions for astaxanthin recovery. The variables evaluated were acid concentration (0.5-4.5 N), hydrolysis time (3.2-16.8 min), and temperature (56-84 degrees C). The highest astaxanthin recovery (99 +/- 0.48%) was achieved with the following condition: temperature (T) of 71 degrees C, time (t) of 17 min, and [HCl] = 3.7 N. The model indicates that high astaxanthin recovery (97%) can be achieved while reducing [HCl] to 2.3 N, positively impacting the cost and safety of this method. Despite the high solubility of astaxanthin in non-polar solvents, the wet cells of H. pluvialis favored the diffusion of solvents with higher water miscibility. Acid hydrolysis, even under the optimal conditions, did not cause total cell wall rupture, indicating that solvent accessibility occurred through microperforations in the cell wall. Overall, the results establish a more profound understanding on conditions for efficient processing of wet H. pluvialis biomass directly from harvesting operation.

Automated summary

The study investigated the extraction of astaxanthin from Haematococcus pluvialis using acid hydrolysis and solid-liquid extraction, finding that the optimal conditions with hydrochloric acid and acetone resulted in a high recovery rate of 99%. Even under optimal conditions, acid hydrolysis did not completely disrupt the cell wall, indicating that solvent accessibility occurred through microperforations.