We introduce an experimental setup allowing continuous monitoring of bacterial fermentation processes by simultaneous optical density (OD) measurements, long-path FTIR headspace monitoring of CO₂, acetaldehyde and ethanol, and liquid Raman spectroscopy of acetate, formate, and phosphate anions, without sampling. We discuss which spectral features are best suited for detection, and how to obtain partial pressures and concentrations by integrations and least squares fitting of spectral features. Noise equivalent detection limits are about 2.6 mM for acetate and 3.6 mM for formate at 5 min integration time, improving to 0.75 mM for acetate and 1.0 mM for formate at 1 h integration. The analytical range extends to at least 1 M with a standard deviation of percentage error of about 8%. The measurement of the anions of the phosphate buffer allows the spectroscopic, in situ determination of the pH of the bacterial suspension via a modified Henderson-Hasselbalch equation in the 6–8 pH range with an accuracy better than 0.1. The 4 m White cell FTIR measurements provide noise equivalent detection limits of 0.21 μbar for acetaldehyde and 0.26 μbar for ethanol in the gas phase, corresponding to 3.2 μM acetaldehyde and 22 μM ethanol in solution, using Henry’s law. The analytical dynamic range exceeds 1 mbar ethanol corresponding to 85 mM in solution. As an application example, the mixed acid fermentation of Escherichia coli is studied. The production of CO₂, ethanol, acetaldehyde, acids such as formate and acetate, and the changes in pH are discussed in the context of the mixed acid fermentation pathways. Formate decomposition into CO₂ and H₂ is found to be governed by a zeroth-order kinetic rate law, showing that adding exogenous formate to a bioreactor with E. coli is expected to have no beneficial effect on the rate of formate decomposition and biohydrogen production.

_{我们引入了一种实验装置，可以通过同步光密度 (OD) 测量、CO 2} 、乙醛和乙醇的长光程 FTIR 顶空监测以及乙酸根、甲酸根和磷酸根阴离子的液体拉曼光谱来连续监测细菌发酵过程，而无需采样。我们讨论哪些光谱特征最适合检测，以及如何通过光谱特征的积分和最小二乘拟合来获得分压和浓度。积分时间 5 分钟时，乙酸盐的噪声等效检测限约为 2.6 mM，甲酸盐的噪声等效检测限约为 3.6 mM，积分时间 1 小时时，乙酸盐的噪声等效检测限提高至 0.75 mM，甲酸盐的噪声等效检测限提高至 1.0 mM。分析范围至少延伸至 1 M，百分比误差的标准偏差约为 8%。磷酸盐缓冲液阴离子的测量允许通过改进的 Henderson-Hasselbalch 方程在 6-8 pH 范围内对细菌悬浮液的 pH 值进行光谱原位测定，精度优于 0.1。使用亨利定律，4 m 白池 FTIR 测量提供的气相乙醛噪声等效检测限为 0.21 μbar，乙醇等效噪声检测限为 0.26 μbar，相当于溶液中的 3.2 μM 乙醛和 22 μM 乙醇。分析动态范围超过 1 mbar 乙醇，相当于溶液中的 85 mM。作为应用实例，对大肠杆菌的混合酸发酵进行了研究。在混合酸发酵途径的背景下讨论了CO ₂、乙醇、乙醛、酸例如甲酸和乙酸的产生以及pH的变化。甲酸盐分解成CO ₂和H ₂被发现受零级动力学速率定律控制，表明向具有E 的生物反应器中添加外源甲酸盐。预计大肠杆菌对甲酸分解速率和生物氢产生没有有益影响。