Table 1.shows that alcohol fermentation using non-immobilized yeast strain resulted in higher alcohol
content compare to the processes using immobilized yeast strain.The ethanol concentration was
determined based on thedensity of alcohol distillate at 16ºC and expressed in volume %(v/v).The highest
alcohol content was produced by yeast strain B with 6.83 % of ethanol concentration. Several theories
have been proposed to explain the reduction in final ethanol concentration during the fermentation using
the immobilized yeast strain due to the formation of a protective layer by the support may act to restrict
the microorganism to reach the substrate [11, 12].
Results presented in Table 1. for immobilized yeast strains indicated that the cells immobilized in
white glutinous rice flour yielded higher alcohol concentration than that of immobilized in rice flour
except for yeast strain A. The highest alcohol content was reached by yeast strain C with 5.4% of ethanol
concentration.
It is also can be seen that the decreasing of pH in the end of the fermentation period affected the
alcohol content. At the constant pH about 4.8, the cells can perform their optimum activity. However it is
found that the pH decreased during fermentation reaction. The higher the final pH, the higher the alcohol
content in the fermentation medium. It might be caused by formation of carboxylic acid derivatives
resulted in lessen of alcohol content.
3.3. Screening of immobilized yeast strain