Effect of aeration and agitation on yeast inulinase production: a biocalorimetric investigation.

Air flow rate and agitation speed for inulinase production by Kluyveromyces marxianus were optimized based on metabolic heat release profiles. Shear stress and oxygen transfer (ka) values were compared to assess the effects of aeration and agitation. At agitation rates of ≤ 100 rpm, the oxygen mass transfer rates were small and eventually led to less inulinase production, but at agitation rates > 150 rpm, loss of biomass resulted in less inulinase activity. Bio-reaction calorimeter (BioRc1e) experiment with aeration rates ≤ 0.5 lpm showed low ka while at 1.5 lpm frothing of reactor contents caused loss of biomass and inulinase activity. The optimum conditions for aeration and agitation rate for K. marxianus in BioRc1e were 1 lpm and 150 rpm. Heat yield values obtained for the substrate, product and biomass reinstated the ongoing metabolic process. The heat release pattern could be a promising tool for optimization of bioprocess and in situ monitoring, with a possibility of interventions during the biotransformation process. At optimized aeration and agitation conditions, a two-fold increase in inulinase activity could be noticed.