Development of solid state biocatalytic nanofibrous membranes for food fermentation

The aim of this PhD project was to develop solid state biocatalytic nanofibrous membranes functionalized with yeast cells for the fermentation of grape juices. The membranes were made of nylon-6 and produced by electrospinning. Nylon-6 was selected because of its inertness toward different chemical conditions and stability. Yeasts were immobilized on the membranes by a drop coating procedure. The functionalized membranes were applied for the fermentation of grape juices and the resulting metabolic activity was monitored by isothermal microcalorimetry. Once immobilized, the yeasts showed always a higher activity (i.e. growth rate) than the yeast freely dispersed. The results also show that immobilized yeasts can be used many times without showing a significant loss of fermentation capacity. Moreover immobilized yeasts exhibited a higher tolerance toward ethanol, likely due to formation of a protective biofilms. Overall, this work provides evidence that the nanostructured nanofibrous membranes are an excellent support for the immobilization of yeasts, show enhanced performances towards fermentation and, finally, exhibit the interesting feature of beeing reused several times without a loss of biocatalytic activity.