溶氧及pH对产朊假丝酵母分批发酵生产谷胱甘肽的影响

Effects of Dissolved Oxygen and pH on Candida utilis Batch Fermentation of Glutathione

在 7L发酵罐中研究了溶氧和pH对产朊假丝酵母分批发酵生产谷胱甘肽的影响。结果表明 ,当葡萄糖浓度为 30g L且通气量控制在 5L min时 ,搅拌转速达到 30 0r min即可满足细胞生长和谷胱甘肽合成对溶解氧的需求。不同pH控制方式对谷胱甘肽分批发酵的影响有较大差异。不控制pH时 ,细胞干重和谷胱甘肽产量比控制pH为 5 5的发酵分别低 2 7%和 95 % ,且有 5 0 %的谷胱甘肽向胞外渗漏。研究了将pH控制在 4 0、4 5、5 0、5 5、6 0和 6 5的谷胱甘肽分批发酵过程 ,发现在pH 5 5时谷胱甘肽总产量最高。用前期研究建立的动力学模型模拟了不同pH (4 0～ 6 5 )下的分批发酵过程 ,并从动力学角度解释了pH对细胞生长和谷胱甘肽合成的影响。

The effects of dissolved oxygen (DO) and pH on glutathione batch fermentation by Candida utilis WSH-02-08 in a 7 liters stirred fermentor were investigated. It was shown that DO concentration is an important factor in glutathione production. With the initial glucose concentration of 30 g/L and a 5 L/min air flow rate, and the agitation rate less than 250 r/min, the DO concentration was not sufficient to satisfy the oxygen requirement during the fermentation. With an agitation rate of more than 300 r/min, the cell growth and glutathione production were enhanced significantly, with the dry cell mass and glutathione production were 20% and 25% higher than that at 200 r/min. When C. utilis WSH 02-08 was cultivated in a batch process without pH control, cell growth and glutathione production were inhibited, likely due to a dramatic decrease in the pH. Intracellular glutathione leakages were observed when the pH was 1 5 or less. To assess the effect of pH on glutathione production, six batch processes controlled at pH 4 0, 4 5, 5 0, 5 5, 6 0 and 6 5 were conducted. The yield was highest at pH 5 5, when the dry cell mass and yield were 27% and 95% respectively higher than fermentation without pH control. The maximal intracellular glutathione content (2 15%) was also achieved at the pH. To improve our understandings on the effect of pH on the batch glutathione production, a modified Logistic equation and Luedeking-Piret equation were used to simulate cell growth and glutathione production, respectively, under different pH. Based on the parameters obtained by the nonlinear estimation, kinetic analysis was performed to elucidate the effect of pH on the batch glutathione production. The process controlled at pH 5 5 was proven to be the best due to the higher value of K I (substrate inhibitory constant in the Logistic equation), lower value of α and higher value of β (slope and intercept in the Luedeking-Piret equation, respectively).