Propionic Acid Fermentation By Immobilized Propionibacteria

Propionic acid fermentation with immobilized propionibacteria was investigated in this research. The special property of the immobilized propionibacteria was compared with that of free cells. We have investigated the effect of the sodium alginate and substrates (glucose, lactic acid, mixed-substrate and huangshui) on the propionic acid fermentation. The results are as followed:1. Three carriers: the sodium alginate, carrageenan and agar were studied. The batch experiment results showed that the sodium alginate carrier with advantage of operating simply, shaping easily, was the best one of the three immobilized materials.2. The optimum concentration of the sodium alginate was 4%. The concentration of CaCL₂ was 2%. The optimum size of the immobilized beads was 3.2～3.7mm. After one month storage in solution of 8.5% NaCl and fermented liquid respectively, the immobilized cells in fermented liquid had more vigorous fermentation ability than in 8.5% NaCl. The immobilized cells can be reutilized for 22 cycles. The activity of immobilized cells were stable for 65 days.3. Compared with free cells , the immobilized cells tolerated lower pH, and adapted to more range temperature and had the ability of more acid-resistant. In the laboratory-scale experiments, we observed that the environment-resistant ability of the immobilized cells was stronger than that of free cells.4. Glucose as the single substrate had higher productivity than that of lactic acid as the single substrate. But when use mixed substrate (glucose and lactic acid) the productivity was higher than that of the single substrate (glucose or lactic acid), During the mixed-substrates fermentation, glucose and lactic acid were consumed simultaneously, but the lactic acid was consumed faster than glucose. These results demonstrated that the mixed-substrate was a better substrate for propionic acid production.5. Huangshui -a by-product of Baijiu brewing (its main components were glucose and lactic acid) also could be used to culture propionibacteria. When huangshui as the substrate, the yield rate of propionic acid was 0. 105g/L·h while in the mixed-substrate (glucose and lactic acid)its was 0.167g/Lh. The results showed that there are other components in huangshui inhibited the fermentation .