Aerobic immobilized yeast cell culture: Influence of cell crowding and age in the immobilizing matrix on continuous culture performance

The objective was to evaluate, in terms of the kinetic parameter values of cells taken from an immobilizing matrix, the effect both of the immobilized cell biomass loading in the solid phase of the matrix and the time the cells had been in the mass transfer limited environment of the matrix. Porous silicone rubber was used as the immobilizing matrix. A material that provides a mechanically strong and biocompatible matrix that can withstand the very active respiratory metabolism and growth rate of aerobic yeast culture and the hydrodynamic shear field in a conventional continuous stirred tank bioreactor. The matrix rubber particles can be steam sterilized insitu in the bioreactor prior to colonisation by the yeast culture. Continuous aerobic culture with the yeast for periods in excess of 1500 hours gave immobilized biomass loadings in the matrix greater than that of natural flocs. Yeast growth kinetics were not affected by long term immobilized cell culture, whilst substrate uptake kinetics became more active, as the cells adapted to the matrix.