From green to orange: The change in biochemical composition of phototrophic-mixotrophic Chromochloris zofingiensis in pilot-scale photobioreactors

Upscaling algal cultures from laboratory to pilot-scale provides important biological and technical insights for larger industrial applications. This is particularly important when screening novel algal species to enter the biochemical and nutraceutical markets. One such novel species is Chromochloris zofingiensis. This species has been identified as a potential industrial competitor to Haematococcus sp. for natural astaxanthin production, due to higher biomass concentrations and quantity of product per unit volume. To test the scalability potential C. zofingiensis was cultured using a phototrophic-mixotrophic approach in 65 L photobioreactors. The biomass increased from 0.05 to 0.51 g/L DW during a 15 day phototrophic phase. The subsequent mixotrophic phase induced carotenogenesis and turned the cells from green to orange. This altered the composition of the biomass and increased the biomass concentration from 0.65 to 5.13 g/L in 8 days. Astaxanthin is the primary compound of interest in this biomass and its concentration per culture increased during the mixotrophic phase; 0, 12.7, and 14.7 mgDW/L on days 0, 5, and 8, respectively. The highest protein, carbohydrate, and lipid concentrations per culture were recorded on day 5 (570, 1760, and 3715 mgDW/L, respectively). This study reports the largest scale use of mixotrophic cultivation of C. zofingiensis available in the literature where astaxanthin production was initiated using glucose (30 g/L), nitrogen deprivation, and a continuous photoperiod with an increased light intensity (245 μmol/m²/s). The findings demonstrate the potential for further scaling to obtain high biomass concentrations at industrial volumes for production of astaxanthin along with additional products as part of a biorefinery process.