EXOPOLYSACCHARIDE PRODUCTION BY FREE AND IMMOBILIZED MICROBIAL CULTURES

The batch production of different exopolysaccharides (alginate, xantha n, pullulan, dextran) by free and immobilized microbial cultures was i nvestigated. First conventional free-cell cultures were performed to o btain control fermentation parameters and macromolecular characteristi cs of exopohysaccharides. Then microbial cultures were immobilized in composite agar layer/microporous membrane structures and tested for po lysaccharide production. The immobilized-cell system proved unsuitable for xanthan and pullulan production. Owing to the fouling of the micr oporous membrane by the polysaccharide, dextran production by immobili zed Leuconostoc mesenteroides also was inefficient. More promising res ults have been obtained with immobilized Azotobacter vinelandii cultur es. The amount of alginate produced by immobilized A. vinelandii repre sented about 60% of that recovered from a free-cell culture, whereas t he polysaccharide yield reached 35% instead of 9% for the free counter part. These results are compared to the macromolecular characteristics of exopolysaccharides.