Production Of Butyric Acid By Immobilized Cell Fermentation In A Rice Bran Fibrous-Bed Bioreactor

Butyric acid is widely used in agricultural, textile, foodstuff, pharmaceutical and feed industries. In the feed industry, sodium butyrate has the characteristics of no pollution, no harmful residues and unique nutritional physiological functions, which makes it become one of the popular alternatives to antibiotics. To reduce the costs of butyric acid fermentation, using cheap feed ingredients as cell immobilized material is an effective option. Two novel fibrous-bed bioreactors with rice bran as cell immobilized material for butyric acid production was established in this study.The amount of carrier and the adsorption of sodium butyrate and Clostridium tyrobutyricum by carrier were studied. The results showed that the suitable carrier dosage was 60 g/L. And the ratio of the adsorption of sodium butyrate was about 0.02-0.08 g/g, which met the proportion of sodium butyrate and rice bran in the feed. Rice bran could adsorb more Clostridium tyrobutyricum than wheat bran, so rice bran was chosen as the immobilized cell material.An inner fibrous-bed bioreactor with rice bran as cell immobilized material for butyric acid production was established. Using Clostridium tyrobutyricum as the fermentation strain, free-cell and immobilized-cell fermentation for butyric acid production were conducted. The results showed that the productivity of immobilized-cell batch fermentation was 0.43 g/L/h, about 38.71% higher than the free cells. Furthermore,21.22 g/L butyrate was achieved by immobilized cells in the repeated batch fermentation and the butyrate production was very stable by using this system. Finally, the sodium butyrate in the fermentation broth can be adsorbed by the rice bran and the ratio of adsorption was about 0.054 g/g. The rice bran could be directly used as feed additive.In order to optimize cell immobilization in rice bran to produce butyric acid, an external fibrous-bed bioreactor with rice bran as cell immobilized material for butyric acid production was established in this study. Using the external fibrous-bed bioreactor, immobilized-cell batch fermentation for butyric acid production was conducted. The results showed that the productivity was 0.48 g/L/h, about 55.21% higher than the free cells. Furthermore,21.05 g/L butyrate was achieved by immobilized cells in the repeated batch fermentation and the butyrate production was also stable by using this system. Finally, the sodium butyrate in the fermentation broth can be adsorbed by the rice bran and the ratio of adsorption was about 0.105 g/g. The rice bran could also be directly used as feed additive after proper dilution.A simple rotary granulation method was designed. Using sodium carboxymethyl cellulose, gum arabic and corn starch as an adhesive respectively, rice bran pellets were made from rice bran containing sodium butyrate. All the adhesives could make rice bran granulated well. The size and water content of rice bran pellet feed could all meet the premix standard of enterprises. The sodium butyrate content contained in the feed could meet the addition ratio of sodium butyrate and rice bran (0.004-0.06 g/g). Taking the cost and affordability into account, corn starch was chosen as an adhesive of rice bran pellets.