Mono- and poly-unsaturated triacylglycerol fractionation from Chlorella sp. using supercritical carbon dioxide

Abstract

Extraction of unsaturated triacylglycerols from microalgae is important towards the viability of a sustainable biorefinery. Supercritical carbon dioxide was used to extract and enrich the mono- and poly-unsaturated triacylglycerols using a step-wise extraction scheme where the supercritical carbon dioxide density was increased from 450 to 550 to 750 mg/ml over a total of 170 min. At the lowest density of 450 mg/ml, saturated fatty acid triacylglycerols comprised 88% (mol) of the extract while mono- and poly-unsaturated triacylglycerols were over 60% and 80% (mol) at 550 and 750 mg/ml supercritical carbon dioxide respectively. This extraction scheme was informed by solubility and intermolecular interactions of mixed triacylglycerols. Chrastil's solubility parameters suggested that saturated fatty acid triacylglycerols were susceptible to intermolecular interactions while mono- and poly-unsaturated triacylglycerols are less susceptible to these interactions. Combined with the low solubility of mono- and poly-unsaturated triacylglycerols and high solubility of saturated fatty acid triacylglycerols at low densities, these phenomena were combined to demonstrate how supercritical carbon dioxide can be tuned to fractionate mono- and poly-unsaturated triacylglycerols from saturated fatty acids from microalgae. This is significant as supercritical carbon dioxide extraction technology is scalable and suitable as a first unit process for separations in a biorefinery setting.