An integrated approach for cheese whey lactose valorisation

Abstract

The development of any fermentation process requires the integration of life and engineering sciences with the aim of obtaining a high productivity system. The use of immobilized cells is, without any doubt, one of the most interesting ways to achieve this purpose, being several the advantages they present. Moreover, they are a clear example of how life and engineering sciences interact in the development of a fermentation process. As the cost of the biomass support material is known to be a limiting factor in the implementation of a continuous high-cell-density fermentation process, the use of low cost immobilization technique is required as is the case of the application of yeast flocculating cells. Substrate must also be available in large amounts and at low cost, as is the case of lactose from cheese whey, a by-product of dairy industry. Results are presented on the development of continuously operating high productivity systems using flocculating yeast cells for the production of ethanol and/or β-galactosidase using lactose from cheese whey as fermentation substrate. The presentation of the results is divided into three main parts - the first one deals with a brief introduction on the state of the art of the different subjects related hereby, namely, the cheese whey problematic, the construction of lactose metabolising S. cerevisiae cells and the use of flocculation in continuous high-cell-density systems. The second part presents results on the construction, using molecular biology techniques, of yeast strains with the ability to form flocs and perform the desired biotransformation being it the production of ethanol or β-galactosidase. The third one deals with the operation, at laboratory scale, of continuous high cell density airlift bioreactors using the previously developed yeast strains.