Optical method for the determination of the oxygen-transfer capacity of small bioreactors based on sulfite oxidation

The growth of microorganisms may be limited by operating conditions which p rovide an inadequate supply of oxygen. To determine the oxygen-transfer cap acities of small-scale bioreactors such as shaking flasks, test tubes, and microtiter plates, a noninvasive easy-to-use optical method based on sulfit e oxidation has been developed. The model system of sodium sulfite was firs t optimized in shaking-flask experiments for this special application. The reaction conditions (pH, buffer, and catalyst concentration) were adjusted to obtain a constant oxygen transfer rate for the whole period of the sulfi te oxidation reaction. The sharp decrease of the pH at the end of the oxida tion, which is typical for this reaction, is visualized by adding a pH dye and used to measure the length of the reaction period. The oxygen-transfer capacity can then be calculated by the oxygen consumed during the complete stoichiometric transformation of sodium sulfite and the visually determined reaction time. The suitability of this optical measuring method for the de termination of oxygen-transfer capacities in small-scale bioreactors was co nfirmed with an independent physical method applying an oxygen electrode. T he correlation factor for the maximum oxygen-transfer capacity between the chemical model system and a culture of Pseudomonas putida CA-3 was determin ed in shaking flasks. The newly developed optical measuring method was fina lly used for the determination of oxygen-transfer capacities of different t ypes of transparent small-scale bioreactors. (C) 2001 John Wiley & Sons, In c.