Advantages in maltose fermentation at extremely low temperatures (5-10°C) using an alcohol resistant and cryotolerant yeast strain (Saccharomyces cerevisiae AXAZ-1) immobilized on porous cellulosic material (or tubular cellulose, TC), produced by delignification of wood sawdust, are reported. Pure maltose and glucose media (80, 100 and 140 g/l) were examined as model substrates to evaluate the potential effect of TC on the rate of fermentation of maltose containing substrates. The use of TC sharply accelerated the rate of maltose fermentation compared to free cells (FC) in suspension. Fermentation at 5°C by immobilized cells was complete, while FC were unable to ferment maltose at this temperature, in contrast to glucose, which was completely fermented. From the results of maltose and glucose fermentations at 5 and 10°C, it was concluded that the effect of TC was higher at lower fermentation temperature and that its promotional effect on fermentation rate had to be at the step of maltose uptake. Specifically, it is suggested that the presence of TC increased maltose uptake rate by the immobilized cells due to attraction by hydrogen bonding on the TC surface and continuous pumping of maltose towards the cells. Calculation of the activation energy of maltose fermentations at 5, 10 and 15°C showed that it was reduced by an average 42% when cells immobilized on TC were used.
Keywords: Activation energy; Immobilized yeast; Low temperature fermentation; Maltose; Porous cellulose.
Copyright © 2014. Published by Elsevier Inc.