Safe and Complete Extraction of Astaxanthin from Haematococcus pluvialis by Efficient Mechanical Disruption of Cyst Cell Wall

Haematococcus pluvialis (H. pluvialis) can naturally accumulate high amounts of astaxanthin - a powerful antioxidant. However, complete recovery of astaxanthin from the cysts of H. pluvialis is challenging because of the presence of a robust acetolysis resistant cell wall. Herein, a simple and effective planetary ball-milling pretreatment was developed to rupture the cells to attain an almost complete recovery of astaxanthin from H. pluvialis, using a supercritical CO2 and conventional organic solvent-based extraction. An optimized pretreatment using planetary ball mill under very mild conditions (150 rpm, 60 min) allowed the recovery of 31.4 mg/g dry weight of astaxanthin from H. pluvialis, while slightly harsh milling (500 rpm) was found to be detrimental toward astaxanthin. The extracts in acetone exhibited higher antioxidant activity in 1-diphenyl-2-picrylhydrazyl assay than those in dichloromethane. These mild conditions were safe and highly effective for the complete extraction of astaxanthin along with the others extractables. This study opens a new avenue for the efficient recovery of valuable thermolabile ketocarotenoid species from microalgae, which can be applied to the development of economically viable biorefineries.