Production of Microbial Rennin in a Continuous System Fermenter and Modelling of the Activity


Abstract: In this work microbial production of rennin, a milk clotting enzyme, from a commericial strain of Mucor miehei (NRRL 3420, USDA) has been investigated in a continuous fermenter. The spherical biofilm type growth of the culture has been accomplished in the fermenter and the effects of operational parameters; medium pH, mixing rate (K.H.), dilution rate (D) and feed D-glucose concentration $(S_{gf)$ on milk clotting activity (S.P.A.) have been elaborated. For a fermenter sample containing 1.24 IU/mL S.P.A., optimum production parameters at 37 °C have been determined as K.H.=400 rpm, D=0.125 day$^{-1$ and $S_{gf$=7.5 g/L without pH control. Under these conditions, the fermenter operated 575 hours continuously producing 10230 IU S.P.A. in total. In the fermenter sample, R factor and specific S.P.A. were deteremined as 1.55x10$^{-3$ S.P.A/P.A. and 5.28 IU/mg protein, respectively, denoting competitive activity of a commercial rennet after concentration. In model simulation studies of the results, maximum S.P.A. obtained has been succesfully represented with a multiple-linear function expressed in terms of fermentation medium pH, D-glucose and dissolved oxygen concentrations and dilution rate. Model simulations also showed that enzyme production rate was solely controlled by fermentation medium characteristics rather than operational fermenter parameters.

Keywords: Rennin, Milk Clotting, Cheese, Mucor miehei, Biofilm

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