of TSC-cell culture, the ethanol production, sugar consumption and
YP/S appeared higher than those in the SC culture. A remarkably
higher stability of the TSC-cell over SC was observed in the fifth
batch. While the final ethanol concentration in the SC system
dropped dramatically to 9.9 g/L in the fifth batch, a final ethanol
concentration of 77.6 g/L was maintained in the TSC-cell system.
High concentrations of ethanol have been reported to inhibit the
growth and metabolism of free S. cerevisiae cells [14]. The enhanced
cell stability of the immobilized cell culture compared to the free
cell culture implies that the TSC carriers may have protected the
yeast cells from toxic conditions during the fermentation process.
The increased stability of the immobilized cells over the nonimmobilized
cells is attributed to the immobilization matrices’
protective effects against the toxicity of metabolic products, as previously
reported [3,4].
The final total cell concentration of the TSC-cell system was
14.6 g/L, which was approximately twice that of the SC system
(7.4 g/L). An increase in the number of yeast cells adsorbed on
the inner/outer surfaces and in the micro-porous structure of the
fibril network of the TSC was observed. As shown in Fig. 3, the