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丙酸是以玉米为原料自絮凝酵母乙醇连续发酵系统废糟液全循环过程中积累的主要抑制物。基于丙酸对酵母细胞抑制机理,开发了3种废糟液全循环条件下乙醇连续发酵工艺策略。首先根据高温导致丙酸生成的现象,去除了物料灭菌环节,使发酵液丙酸浓度显著降低,生物量和乙醇浓度分别提高了59.3%和7.4%。其次,以丙酸浓度达到半数抑制浓度(IC50)40 mmol/L为目标,通过拟合丙酸积累数据预测废糟液全循环的最长运行时间,发酵装置运行应控制在此时间范围内。再次,较低的环境pH值提高了丙酸毒性,而实验证明发酵液pH为5.5时,丙酸对细胞生长的抑制影响最小,因此控制发酵过程中的pH有利于弱化丙酸毒性。
Propionic acid is the main inhibitor accumulated during the whole circulation of waste liquid of continuous fermentation system of ethanol from corn with self-flocculating yeast. Based on the inhibitory mechanism of propionic acid on yeast cells, three kinds of continuous fermentation process strategies of ethanol waste were developed. First of all, according to the phenomenon of high temperature leading to the formation of propionic acid, the sterilization of the material was removed, the concentration of propionic acid in fermentation broth was significantly reduced, and the biomass and ethanol concentration were increased by 59.3% and 7.4% respectively. Secondly, aiming at the concentration of propionic acid reaching 50% inhibition concentration (IC50) of 40 mmol / L, the longest running time of waste circulation was predicted by fitting the data of propionic acid accumulation. The operation of fermentation unit should be controlled within this time range. Third, lower environmental pH increases the toxicity of propionic acid. Experiments show that propionic acid has the least inhibitory effect on the cell growth when the pH of the fermentation broth is 5.5. Therefore, controlling the pH during the fermentation is beneficial to weaken the propionic acid toxicity.