Automatic fermentation control based on a real-time in situ SIRE® biosensor regulated glucose feed

Monitoring and regulation of fermentations is of a paramount industrial and academic importance in order to keep conditions optimal during the entire process. Established techniques employed today include HPLC and spectrophotometry, which both have the disadvantage that broth samples have to be drawn from the fermentor and that they often require sample pre-treatment. The objectives of this study was to design and evaluate a software controlled automatic real-time SIRE® biosensor connected to a glucose feed solution pump for in situ based monitoring and regulation of the glucose concentration during a yeast fermentation process.The maximal frequency for the measuring-regulation cycles was 30/h. A 10 mM mean glucose concentration level was successfully maintained within ±0.013 mM during 60 min fermentations at various concentrations of yeast (10, 20, 40 and 80 g/l). The on/off-regulator used caused some expected fluctuations (oscillations) of the glucose concentration around the mean value (±0.12 mM at 10 g/l, ±0.26 mM at 20 g/l, ±0.51 mM at 40 g/l, and ±0.99 mM at 80 g/l).A 7-h fermentation process (10 mM glucose and 20 g/l yeast) was successfully monitored and regulated. The obtained measuring data were found to be 8.5–22.9% lower than data obtained with a commercially available spectrophotometric kit. The difference increased linearly (−0.26 mM/h), during the fermentation process and indicated that some clogging of the in situ positioned probe occurred. The speed and the automatisation adaptability of the presented device suggest advantages compared to established techniques.