Effect of Continuous Fermentation of High-Sugar Fruit Must on the Viability and Morphology of Immobilized Yeast on White Foam Glass

Sylwia Bonin* and Joanna Skwira

Department of Food Biotechnology and Microbiology, Faculty of Food Sciences, Warsaw Agricultural University, ul. Nowoursynowska 169C, PL-02767 Warsaw, Poland

Article history:
Received April 29, 2006
Accepted September 25, 2007

Key words:
continuous fermentation, immobilization, yeast, morphology

Summary:
We studied the effect of continuous fermentation of high-sugar fruit must (containing about 320 g/L of total sugars) on the viability and morphology of yeast cells. The process was carried out for 2.5 months in a 4-column bioreactor at 22 °C, using the Saccharomyces bayanus S.o./1AD wine yeast strain, which was immobilized on cubes of white foam glass. During the time of continuous fermentation, the apple wine contained 11.4–16.8 % (by volume) of alcohol and a total sugar concentration of 49.2–115.4 g/L. Yeast cells isolated from the carrier at the end of continuous fermentation were bigger than the cells before immobilization and were characterized by various shapes, e.g. they were elongated, large and round or pear-shaped. Some cells were connected to other cells in the form of aggregates. Some yeast cells from the second, third and fourth columns showed a substantial number of wrinkles or folds. Moreover, it was observed that yeast from the carrier in the first column was characterized by the highest viability, 70 %. In the fourth column, the percentage of viable cells was only 11 %.

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