Study On The Screening And High Cell Density Culture Of Zearalenone Elimination Yeast

Zearalenone (ZEN) is widely found in moldy grain crops and dairy products, which has a strong reproductive toxicity and carcinogenicity. It has a huge impact on livestock breeding. A ZEN elimination yeast CLY01 has been identified. To obtain high concentrations of CLY01, the optimized cultural conditions and high cell density fermentation of CLY01 were investigated. The cell drying process was investigated for the further study of obtaining the fed yeast which has the capacity of zearalenone elimination.Yeast CLY01 was fermented in the must which contains ZEN. It's found that the concentration of ZEA decreased greatly after 96 h fermentation by means of HPLC. The ZEN elimination rate is 96.66 % which is much higher than that of heat-inactivated CLY01 yeast and Saccharomyces cerevisiae. The result indicates that the viable CLY01 has the capacity of zearalenone elimination.The optimized cultural conditions of CLY01 were investigated. The results of single factor experiment and orthogonal experiment showed that the most favorable cultural conditions were glucose 15 %, soybean meal 2 %, wheat bran hydrolyzete 4 %, KH2PO4 0.4 %, MgSO4 0.25 %, pH value 4.5, inoculum 10%, shaker speed 200 rpm. Being cultivated under the optimized cultural conditions for 24 h at 30℃, the viable counts of CLY01 were 1.64×10~9 cfu/ml and enhanced the cell concentration about 2 times.High cell density fermentation of CLY01 was studied in a 5 L fermentor. The optimized agitation speed was 200 rpm. On the base of the determination of yeast growth curve under high cell density fermentation, controlling pH 4.5 by auto-feeding glucose and (NH4 )2 SO4 to promote the growth of cells. Being cultivated under the optimized cultural conditions (liquid volume 3L, pO2 30 %, agitation speed 200 rpm) for 72 h at 30℃, the viable counts of CLY01 were 3.86×10~9 cfu/ml which is as 2.35 times as the shake flask's.To determine the process of CLY01 powder production, the centrifugal condition, hot air drying process and protectant for hot air drying yeast were studied. Results indicate that the optimized centrifugal conditions for CLY01 is under 6000 rpm in rotational speed for 5 min and the centrifugation yield ratio of yeast can reach to 85.28 %. The CLY01 was mixed with the optimum protectant 5% sorbitol and the survival ratio was 9.33 % after 12 h hot air drying at 50℃. The survival ratio of the yeast mixed with sorbitol is as 7 times as the one not have sorbitol. Under the optimized process of CLY01 powder production, the survival ratio of CLY01 powder is about 7.96 %.