Process integration of supercritical carbon dioxide extraction and acid treatment for astaxanthin extraction from a vegetative microalga

Astaxanthin (AXA) is a carotenoid with strong antioxidant activity that has been reported to have beneficial effects on human health. Unlike the case of Haematococcus pluvialis cysts, the study of other AXA-producing vegetative microalgae as alternative AXA sources has been minimal, because of inefficient AXA extraction yield and difficulty in separating chlorophyll and AXA. In this study, a novel method was developed to extract AXA from a vegetative green microalga (Monoraphidium sp. GK12) and to separate chlorophyll and AXA using a supercritical-CO2 extraction (SCE) and acid treatment. AXA in the microalgal biomass was extracted completely by SCE, while simple ethanol soaking could not extract AXA well. The addition of ethanol as a co-solvent improved AXA extraction yield. The method employed low CO2 pressure and reaction temperature as well as a short reaction time, making it energy-efficient. Chlorophyll in AXA-containing extract was easily removed by acid addition (H2SO4 or HCl) and centrifugation. Since those acids can be neutralized by alkaline, which produces nontoxic salt, and AXA in the extract can be condensed by reducing pressure, the developed method is expected to stimulate commercialization of a vegetative microalga as an alternative AXA source for food applications. (C) 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.