3.4.1 Preparation of immobilized yeast cells

Of the various methods used for continuous fermentation, that employing the use of immobilized yeast cells was selected. Methods of yeast immobilization evaluated included collagen casting, acetic acid-lactic acid cellulose microencapsulation, chitosan/glutar-aldehyde molding, carrageenan-entrapping method, and calcium alginate gel-entrapping. Of these, the calcium alginate gel-entrapping method was preferred because of its high enzymatic activity, simple manner of preparation, and stability.

Preparation of a uniform calcium alginate gel, necessitated maintaining the viscosity of the mixture of calcium alginate and yeast cells between 1000 and 2000 cps. The addition of a nonionic surfactant and an unsaturated fatty acid at the time of gelling was also found to improve cell retention and enzyme activity. Preparation of immobilized yeast cells is outlined in Fig 3-15.