In order for the production of Phaffia rhodozyma to be commercially viable, biomass yield (productivity) and astaxanthin production have to be high. However, both biomass productivity and astaxanthin production of P. rhodozyma depends strongly on the concentrations of both C- and N-sources. When the concentration of glucose (C-source) in the medium is high, the metabolism of yeast is fermentative rather than respiratory leading also to a rather low conversion efficiency of glucose to cellular biomass and, as a result, low biomass productivity. On the other hand, when the concentration of glucose is low, the metabolism of yeasts is completely respiratory instead of fermentative resulting in a significantly high efficiency of conversion of glucose to cellular biomass. Further, nitrogen (N) sources such as beef extract, yeast extract and potassium nitrate were shown to play an important role on the level of astaxanthin production.
Additionally, in batch cultivation of P. rhodozyma, both biomass productivity and astaxanthin content is also low because of the glucose repression effect since somewhat high glucose concentrations are used. In continuous culture, when high dilution rate is used, the cellular biomass yield is high. On the contrary, when dilute rate is low, the biomass productivity falls. However, for both cases, productivities astaxanthin is relatively low compared even with that of the batch cultivation.