Phaffia rhodozyma Cultivation on Structural and Non-Structural Sugars from Sweet Sorghum for Astaxanthin Generation

ABSTRACT Because it contains both structural and non-structural sugars, sweet sorghum has potential applications in biorefineries seeking to produce co-products. Differences between sugar composition in sweet sorghum juice (SSJ) and sweet sorghum bagasse (SSB) requires a robust organism that can be cultivated in both sources. The red pigmented yeast strain Phaffia rhodozyma can be grown indiscriminately on sugars originating from agricultural feedstocks and produces the carotenoid astaxanthin which has applications in high value markets. In this study we determined cultivating conditions for Phaffia rhodozyma in both SSJ and SSB hydrolysate for biomass growth and astaxanthin generation. Batch bioreactor studies on SSJ with supplementation produced 34.9 g/L biomass with 53.3 mg/L astaxanthin at a productivity rate of 0.352 mg/L/h after 168 hours of cultivation. Phaffia cultivated in SSB hydrolysate showed improved growth after activated carbon (AC) detoxification and only marginal improvement after laccase detoxification. AC detoxification produced 23.6 g/L biomass, 48.89 mg/L astaxanthin, and a productivity of 0.291 mg/L/h. Undiluted SSB hydrolysate produced inferior results due to the assumed presence of phenolic inhibitors. While both structural and non-structural sugars from sweet sorghum can be utilized by Phaffia rhodozyma , it is apparent that SSJ provides a better substrate to produce naturally occurring astaxanthin.