APPLICATION OF FUZZY CONTROL-SYSTEM TO COENZYME-Q10 FERMENTATION

A fuzzy control system for a fed-batch culture was constructed and applied to coenzyme Q10 fermentation. For inputs, cell concentration ([OD] and [OD2]), specific growth rate ([SGR]) and fermentation time ([BTIM]) were selected. A base value of aeration rate ([AIRB]) and an adjustment term for [AIRB] ([DAIR]) were defined as outputs. In this system, cell concentration was measured on-line by a turbidimeter and specific growth rate was then calculated. After cell concentration, specific growth rate and fermentation time were transferred into four inputs using membership functions, and these were further transferred into two outputs by 70 fuzzy rules. After defuzzification of [AIRB] and [DAIR], a set value of the aeration rate was determined as the sum of defuzzied [AIRB] and [DAIR]. In this fuzzy control system, the aeration rate was set at two-hour intervals according to its state and the productivity was higher and had less deviation than model fermentation (predetermined stepwise shift up each 20 hours in the aeration condition). Such result was also obtained even in the case of low initial cell concentration. These data indicated the usability and stability of this fuzzy control system.