Microalgal production of zeaxanthin

Abstract

Zeaxanthin is a carotenoid pigment used in the food industry as well as in supplements for age-related macular degeneration. There is potential for microalgae to be used for zeaxanthin production, however there is relatively little work examining this issue, particularly with respect to scale-up. Here two species of cyanobacteria (Synechococcus sp. PCC7002 and Synechocystis sp. PCC6803) were examined, along with a Rhodophyte (Rhodosorus sp.). At a light intensity of 80 μmol photons m−2 s−1 specific zeaxanthin contents were 2.30 ± 0.84, 1.61 ± 0.68 and 2.16 ± 0.63 mg g−1 for Synechococcus sp. PCC7002, Synechocystis sp. PCC6803 and Rhodosorus sp., respectively. Of the species examined the Synechococcus PCC7002 had the highest specific growth rate (0.74 ± 0.09 day−1). This species was used to further optimize the process, increasing the nutrient concentration in the medium and using an incremental light addition strategy led to an approximately 13-fold increase in the cell density, giving a final dry cell weight of 4.25 ± 1.42 g L−1. Results from this work are among the highest in the literature for zeaxanthin productivity (0.7 ± 0.5 mg L−1 day−1) and the approach used can be readily scaled-up. Additionally, the approach used in this work to achieve high cell densities of PCC7002 could be potentially applied to the production of other compounds (e.g. phycobilins or compounds produced using metabolic engineering).