PRODUCTION OF FERMENTED FLAVORED LIQUID B Y REPEATED BATCH FERMENTATION USING IMMOBILIZED YEAST-CELLS

To efficiently produce a fermented flavored liquid for improving the t aste of bread, we studied repeated batch fermentation in a bioreactor with the use of immobilized yeast cells. By using the bioreactor, a fe rmented flavored liquid containing about 5% (w/v) ethanol could be con stantly produced. However, the bacterial count in the fermented flavor ed liquid gradually increased as the batch fermentation was repeated a nd reached 10(7) CFU/ml on the day 12. The growth of the bacteria sepa rated from the fermented flavored liquid could be stopped at a lactic acid concentration of 0.25% (w/v). Lactic acid at this level did not a ffect the growth of the test yeast. When 0.4% (w/v) of lactic acid was added at the initiation of the culture in the repeated batch fermenta tion, the bacterial count in the fermented flavored liquid rapidly dec reased and reached almost 0. An increase in the bacterial count could be inhibited by subsequently adding 0.2% (w/v) of lactic acid. When th e addition of lactic acid was ceased, there was observed a tendency to ward an increase in the bacterial count. After storing at 10 degrees C for 16 days, the immobilized yeast cells enabled the production of th e fermented flavored liquid similar to the one before storing. Regardi ng the major flavoring components in the fermented flavored liquid, th e concentrations of ethyl acetete, isoamyl alcohol and isobutyl alcoho l remained relatively constant, while organic acid concentrations cons iderably varied.