Utilization of Sweet Sorghum Juice for the Production of Astaxanthin as a Biorefinery Co-Product by Phaffia rhodozyma

This work investigates cultivating the red-pigmented yeast Phaffia rhodozyma in sweet sorghum juice (SSJ) to assess the production of astaxanthin as a potential biorefinery co-product. Shake flask cultures on defined sugar medium indicated that all three sugars (sucrose, glucose, and fructose) could be consumed with adequate nitrogen and nutrient supplementation. Only modest biomass growth and astaxanthin production could be achieved in SSJ without nitrogen supplementation; however, combining nitrogen supplementation with yeast extract in diluted SSJ could metabolize all sugars present in 168 h. A 2 L bioreactor trial with full strength (i.e., undiluted) SSJ produced up to 29 g/L of biomass, 65.4 mg/L of astaxanthin, an overall cell astaxanthin content of 2.49 mg astaxanthin/g dry cell mass, and a volumetric astaxanthin productivity of 0.389 mg/L/h after 168 h of cultivation. Further process optimization is needed since glucose metabolism was incomplete in undiluted SSJ.