RESUMO
Astaxanthin is a useful pigmentation source in fish aquaculture. It has strong antioxidative activity and therefore has potential application in delaying aging and degenerative diseases in human and animals. In recent years, there is a growing demand for astaxanthin. The red yeast Xanthophyllomyces dendrorhous (called Phaffia rhodozyma before) is one of the most promising microorganisms for the commercial production of astaxanthin. During fermentation, X. dendrorhous shows the Crabtree effect. Higher glucose concentration will cause significant reductions in biomass and astaxanthin production. Therefore, fed-batch processes are particularly useful. In this paper, effects of glucose-feeding strategies on astaxanthin production by X. dendrorhous were studied. Based on the substrate inhibition model, an optimized two-stage feeding strategy for astaxanthin production of high-cell-density fermentation was proposed. Glucose concentration was first controlled at about 25 g/L during the lag phase and the early exponential phase. In such case, biomass could reach its maximum value in relatively short time. Then the glucose concentration was controlled at about 5 g/L in the later exponential phase and stationary phase. The synthesis of astaxanthin could be effectively prolonged. The results showed that the optimized two-stage feeding strategy was the best among all the feeding strategies, and could obtain the highest biomass (23.8 g/L) and astaxanthin production (29.05 mg/L), which was a significant increase (52.8% and 109% respectively) compared with a batch process.