Growth and carotenoid production by pH-stat cultures of Phaffia rhodozyma

To optimize biomass and carotenoid production by Phaffia rhodozyma in pH-stat cultures, two methods of feeding glucose were studied. In the first method, which is comparatively simple to operate, the glucose feeding set point (pH 5.02) was higher than the culture pH (5.00) and P. rhodozyma grew at a low specific growth rate (=0.055 h^–1). In the second method, the glucose feeding set point (pH 4.98) was lower than the culture pH (5.00) and the yeast grew at a specific growth rate of =0.095 h^–1. With the second method of glucose feeding, which is more complex and in order to prevent overfeeding of glucose, a time interval was added to the control strategy of the glucose pump and allowed to expire before the next dose of glucose was added. The length of the time interval affected biomass and carotenoid production. A critical time interval (T_c) was defined. In pH-stat cultures of P. rhodozyma, it was found that if the time interval was set longer than the critical time interval, the yeast did not grow.