Role of bacteria in industrial alcohol fermentation

Primary screening of bacteria responsible for acid formation during alcoholic fermentation indicated that they were lactobacilli. Further identification showed that they are Lactobacillus fermentum (T-3.29.12), L. buchneri (T-3.31.1, v-2.6, v-4.3) and L. brevis (v-5.5) which were heterofermentative. Homofermentative bacteria, L. del brueckii (x-7.4.12) was identified as well. However, L. buchneri (v-4.3) yielded high acid content among the groups. Opitimum pH and temperature of these bacteria were 4.0-8.0 and 37 deg. C. respectively. Temperature above 45 deg. C. and below 20 deg. C. reduced their growth rate. They could utilize biotin and niacin which are presently abundant in molasses for growth. All of the lactobacilli grew in MY broth medium containing 8-12 percent ethanol. Aeration at the rate of 0.5 vvm or above in culture broth decreased growth rate and acid production. Concentration of sulfuric acid at 0.2-0.4 percent could inhibited growth of isolated bacteria. L. fermentum (T-3.29.12) was inhibiteded by K2S205 100 ppm (pH 4.5), while L. buchneri (v-4.3), L. brevis (v-5.5) and L. delbrueckii (x-7.4.12) were inhibiteded at the concentration of 200 ppm (pH 4.5). Penicillin G, kanamycin, streptomycin, chloramphenicol and tetracycline were the antibiotics used for studying the inhibitedory effects. Penicillin G at the concentration of 1-2 ppm showed the largest clear zone among them. Alcohol fermentation by S. cerevisiae Sc. 90 in 2 1 fermentor using sterile molasses medium (18 percent reducing sugar) reinoculated with 10 to the seven power cells/ml. of L. buchneri (v-4.3) and aeration rate of 0.5-0.7 vvm. yielded 8.4 percent (v/v) ethanol within 24 hours. Without aeration ethanol yield was only 4.6 percent (v/v) after 36 hours. In non-sterile medium containing 18 percent reducing sugar, total bacteria count of the fermented mash was 10 to the six power cells/ml. Combination of the treatments, i.e., 2 ppm penicillin G, 0.3 percent sulfuric acid and aeration at 0.6 vvm increased ethanol yield from 6.4 percent (v/v) to 8.2 percent (v/v) as compared with control