Respiration studies of penicillin solid-state fermentation.

An earlier work showed that when the bagasse content (BC) of the solid medium was decreased within a wide range of values, penicillin production by solid-state fermentation was always increased. Respiration studies were performed to understand how BC controls the secondary metabolism in this culture system. CO2 production of solid cultures with different compositions was monitored. In cultures of series A, the initial moisture content was increased and this variation was compensated by decreasing the nutrient and BC of the medium. In series B the initial moisture content was increased while BC was decreased and the nutrient content increased. In addition, penicillin production and respiration was also studied in extreme media (dry and concentrated and humid and diluted), with high and low BC. Criteria for the interpretation of respiration kinetics of the idiophase were established for the first time in this work. For the cumulative form (total CO2/g dry matter vs t) as well as for derivative (CO2/g dm/h vs t) respiration kinetics, the CO2 production rate (Q(CO2)) was determined by calculating the slope of the cumulative curve. Results indicate that Q(CO2) of the tropho- and idiophases was directly related to the BC of the solid medium (and inversely related to penicillin yields). These conclusions were confirmed by analysis of the derivative form, the results of which indicate that a lower but stable metabolic activity is essential for obtaining high penicillin yields in solid-state fermentation (SSF). The results indicate that the derivative CO2 production kinetics proved to be a more precise and sensitive indicator of the culture metabolic activity during idiophase than the cumulative respiration kinetics.