The Studies Of Gluconobacter Melanogenus On The High Concentration Sorbitol Conversion

In vitamin C fermentation industry, the important step is the conversion of L-sorbose from D-sorbitol by microorganism. As the oxidation rate of batch fermentation decreased obviously with the high initial sorbitol concentration, L-sorbitol yield decrease. In the paper, the substance concentration was studied in the vitamin C fermentation technique of Gluconobacter melanogenu and the fermentiton conditions of microorganism in 35%sorbitol liquid medium were investigated.The results showed that the higher substance concentration was, the more obvious inhibition effects were. High concentration of substance and products inhibited the production of sorbose at the initial sorbitol concentration of 30 and 35 percent, however, the microorganism could defend the inhibite effects. So the Gluconobacter melanogenus had a high endurance to the concentration sorbitol and sorbose and a rate of convertion fromD-sorbitol to L-sorbose.The fermentation results showed the growth of Gluconobacter melanogenus was affected by both pH and the concentration of sorbitol while the production of sorbose was influenced by pH and growth state of microorganism in 35%sorbitol liquid medium. The more active the microorganism grew, the slower the production speed of sorbose was.The factors affecting growth metabolism, such as volume of Erlenmeyer flask, pH, inoculum and the concentration of calcium carbonate were investigated. The results showed that the optimal culture condition were 180 mL of medium in a 750 mL Erlenmeyer flask and pH ranged 5.0-6.0 after inoculation and not below 4.1 in fermentation terminal. The optimal inoculation was the medium in fermentation terminal. The optimal concentration of calcium carbonate was 0.7 percent which could regulate pH and accelerate the production of sorbose.The optimized fermentation results showed the inhibited effects of high concentration sorbose were alleviated. The concentration of sorbose reached 362 mg·mL-1 and the production velocity of sorbose was 12.1 mg·mL-1·h-1 in 35% sorbitol liquid medium at 30 h after inoculation.