Loofa reinforced gel carriers for yeast immobilization in ethanol fermentation

Abstract

To comply with energy crisis, ethanol has re-emerged as an alternative to, or extender for petroleum based liquid fuels. As compared to other methods, ethanol production using immobilized cell carriers offer many advantages such as high productivity and reusability. However, application of present cell carries is often hindered by many problems including mass transfer limitation and low mechanical strength. Therefore, a new type of cell carrier called loofa reinforced gel was developed in this study and its feasibility for ethanol fermentation was evaluated and compared with suspended with suspended cell culture and alginate bead. Flocculating yeast strain, Saccharomyces cereviceac M30 was used as the ethanol producer. The fermentation was carried out in flask culture system at shaking frequency of 150 rpm and temperature of 33 ํC. Loofa sponge, chitosan, and alginate were used as materials for constructing the carrier Palm sugar and molasses were used as carbon and energy source. The compared immobilization methods were cell adcorption and entrapment. Reusability of the carrier was evaluated by repeated batch mode. In the preliminary test, loofa sponge alone was found to be inadequate for yeast immobilization. Entrapment method was proven to be more effective than adsorption for yeast immobilization. Chitosan based carriers were unfavorable for yeast immobilization because of their inhibitory effect on cell activity. On the other hand, one type of alginate-loofa carrier namely entrapment alginate-loofa cube (EALC) exhibited promising resulth. Even though EALC had considerably large dimension (8 x 8 x 1 mm), its fermentation performance in term of ethanol yield and production rate was comparable with compact size alginate bead (is an empty set 2 mm). Under SEM analysis, it was shown that EALC posses a more porous structure than alginate bead. It is proposed that the structure distinction was the main factor responsible for the reduction of mass transfer limitation in EALC. Furthermore, EALC was successfully applied in repeated batch fermentation using molasses as the carbon source. During the repeated batch, ethnol production of EALC culture was more stabile than suspended cell culture. With a strong matrix of cellulose inside, potential advantages including altered mechanical strength. Based on the results of this work. subsequent studies especially in larger scale is recommended to ameliorate the full potential of the new EALC carrier in ethanol fermentation.