恒化培养过程中酵母絮凝性状退化行为

De-flocculating behavior of flocculating yeast SPSC01 under chemostat conditions

采用激光聚焦反射颗粒测量系统对自絮凝颗粒酵母恒化培养条件下絮凝状态进行了监测,研究了絮凝性状退化行为。结果表明,在培养基糖浓度为50g·L-1,添加4g·L-1酵母粉和3g·L-1蛋白胨,流加稀释率为0.12h-1条件下,连续培养15d后,培养液中游离酵母细胞数量开始增加,颗粒群体平均粒径逐渐向小尺度方向移动,出现了絮凝性状退化现象。进行了絮凝酵母和退化后得到游离酵母的生长和发酵性能对比实验,发现游离酵母细胞在生长方面比絮凝细胞具有优势,但是乙醇耐性有所降低,由此推断,出现絮凝性状退化的主要原因是游离细胞和絮凝细胞的生长差异和培养过程操作方式的不同。建立了絮凝退化动态模型,模拟了实验结果。对各参数影响进行分析,表明改善种子罐对絮凝酵母的截流效果可以有效防止絮凝退化现象的发生,进而通过在反应器中设置截流挡板,实现了絮凝细胞絮凝性状的维持。

The de-flocculating of the flocculating yeast SPSC01 under chemostat conditions was monitored with the focused beam reflectance measurement system （FBRM） . When the medium containing 50 g · L^-1 glucose, supplemented with 4 g · L^-1 yeast extract and 3 g · L^-1 peptone was fed at the dilution rate of 0.12 h^-1, the size of the yeast floes started to decrease in 15 days, indicating the occurrence of deflocculating of the culture system. Batch culture and fermentation demonstrated that the free yeast cells deflocculated from the yeast floes grew faster but less tolerant to ethanol inhibition, making the chemostat culture system more favorable for them to grow and overtake the yeast floes with extension of the culture period. A dynamic model was developed to simulate this de-flocculating process and the impact of deflocculating probability, dilution rate, growth kinetic parameters, and a bioreactor operation model was further analyzed. It was expected that the improvement of the retention of the yeast floes within the bioreactor could effectively prevent the de-flocculating from oecurring, which was validated by installing a baffle within the bioreactor to retain the yeast floes.