COIMMOBILIZATION OF 3 STRAINS OF MICROORGANISMS AND ITS APPLICATION IN ETHANOL-PRODUCTION FROM RAW STARCH UNDER UNSTERILE CONDITIONS

The suitability of co-immobilized Aspergillus awamori (A) and Zymomonas mobilis (Z) (A-Z system), and of Rhizopus japonicus (R) and Z. mobilis (R-Z system) for direct ethanol production from raw starch was studied. It was observed that in both systems, the fermentation time was very long, the ethanol yield was very low, and the pH decreased below 4.0, while there was high leakage of cells from the gel beads. Although the glucoamylase activity was higher in the R-Z system, the A-Z system showed higher alpha-amylase activity. When the 3 strains of microorganisms were co-immobilized (A-R-Z system), there was a higher rate of raw starch hydrolysis but the ethanol production was only 50% of that obtained with the A-Z system. By changing the fermentation condition to an anaerobic state after 18 h of aerobic fermentation (A-R-Z 18 system), there was no cell leakage from the gel beads, and the pH remained at about 4.8 during the cultivation, while the ethanol yield from raw starch was 96% of the theoretical value. Furthermore, by adding 0.1-0.2% Vantocil IB (an antibiotic) to the fermentation medium, direct ethanol production from raw starch was possible without heat sterilization of the medium and apparatus.