DEVELOPMENT OF A FERMENTATION METHOD USING IMMOBILIZED CELLS UNDER UNSTERILE CONDITIONS .1. PROTECTION OF IMMOBILIZED CELLS AGAINST ANTIMICROBIAL SUBSTANCES

A method of protecting immobilized cells against inhibitory substances in the fermentation medium was investigated with the aim of developin g a process for fermentation under unsterile conditions. It was found that yeast cells could be protected against the inhibitory effects of p-hydroxybenzoic acid esters by co-immobilizing the cells with vegetab le oils. In such a system, the cells grow only in the water phase of t he gel beads where most components of the fermentation medium are reta ined. On the other hand, the p-hydroxybenzoate that diffuses into the gel beads is retained mainly in the oil phase of the beads. Consequent ly, the p-hydroxybenzoate concentration in the water phase remains too low to inhibit the metabolic activities of the immobilized cells. The effectiveness of a vegetable oil in protecting the immobilized cells against an inhibitory substance depends on the partition coefficient o f the substance between the oil and water, the concentration of the oi l and the initial cell concentration.