(214c) Astaxanthin and Triglyceride Co-Products from Microalgae with Sequential Supercritical Carbon Dioxide Selective Extraction Schemes

Microalgae are a promising feedstock for renewable chemicals because of their fast growth, high lipid content, and relatively low environmental impact. Numerous studies have demonstrated techniques for extracting and converting microalgae triglycerides (TAG) to biodiesel or using the lipids as food ingredients or polymers based on their carbon chain length and degree of saturation. In addition to lipids, numerous strains of microalgae contain unique bio-active compounds which can help enable an integrated biorefinery system which produces multiple products from biomass.

One bio-active compound of interest is the carotenoid astaxanthin. These molecules have gained popularity in recent years as anti-oxidant nutritional supplements and whose market value is expected to increase. This work demonstrates how supercritical carbon dioxide (scCO₂) can be tuned to first extract and enrich TAG from microalgae then pressure-tuned to extract and enrich for astaxanthin, a high value carotenoid.

Fundamental investigations of polarity and hydrogen bond behavior of scCO₂ with TAG and astaxanthin solutes provided a theoretical approach towards developing a separation scheme for selective extractions. This information was then used for applied extractions of TAG and astaxanthin from microalgae. Results show how a single continuous extraction process can yield 95% TAG extract followed by 75% astaxanthin extract.

The first set of conditions produced a moderate scCO₂ density and the extract was over 95% TAG. Enrichment conditions which employed a higher scCO₂ density had an extract of over 70% astaxanthin. By utilizing dynamic conditions for a single continuous extraction, fractionation of the two compounds types was achieved on a bench scale apparatus. By enriching value added co-products with scCO₂ separations, the potential valorization of the yielded products as well as additional processing of the residual biomass has implications towards biorefinery separations.