Comparison between immobilized Kluyveromyces fragilis and Saccharomyces cerevisiae coimmobilized with β‐galactosidase, with respect to continuous ethanol production from concentrated whey permeate

Abstract

Kluyveromyces fragilis immobilized in calcium alginate gel was compared to Saccharomyces cerevisiae coimmobilized with β‐galactosidase, for continuous ethanol production from whey permeate in packed‐bed‐type columns. Four different whey concentrations were studied, equivalent to 4.5, 10, 15, and 20% lactose, respectively. In all cases the coimmobilized preparation produced more ethanol than K. fragilis. The study went on for more than 5 weeks. K. fragilis showed a decline in activity after 20 days, while the coimmobilized preparation was stableduring the entrire investigation. Under experimental conditions theoretical yields of ethanol were obtained from 4.5 and 10% lactose substrates with the coimmobilized system. Using 15% lactose substrate, theoretical yields were only obtained when a galactose‐adapted immobilized S. cerevisiae column was run in series with the coimmobilized column. Then a maximum of 71 g/L ethanol was produced with a productivity of 2.5 g/L h. The coimmobilized column alone gave a maximum ethanol concentration of 52 g/L with a productivity of 4.5 g/L h, whereas immobolized K. fragilis only produced 13 g/L ethanol with a productivity of 1.1 g/L h. It was not possible to obtain theoretical yields of ethanol from the highest substrate concentration. Copyright © 1985 John Wiley & Sons, Inc.