Fermentation kinetics monitoring

Monitoring temperature and density during fermentation kinetics has already been described (Sections 3.2.2 and 3.2.3). It is indispensable in winemaking. Other controls are also recommended to complement this data. 

Juice density is measured daily to monitor alcoholic fermentation kinetics. When the density drops to approximately 0.994-0.993, sngar concentrations are then measured daily to verify the completion of fermentation. Fermentation is considered complete when less than 2 g of redncing sugars per liter remain. The fermentors are then carefully topped off. Subsequent operations depend on whether malolactic fermentation is carried ont. 

Applications of chemical kinetics to enzyme-catalyzed reactions soon followed. Because of the ease with which its progress could be monitored polarimetrically, enzyme hydrolysis of sucrose by invertase was a popular system for study. O Sullivan and Tompson (1890) concluded that the reaction obeyed the Law of Mass Action and in a paper entitled, Invertase A Contribution to the History of an Enzyme or Unorganized Ferment , they wrote [Enzymes] possess a life function without life. Is there anything [in their actions] which can be distinguished from ordinary chemical action ... 

KNIGHTS163 devised a procedure for determining the kinetic constants of a batch fermentation system which involves monitoring both the biomass and substrate concentrations, but without assuming a constant yield coefficient. Exponential growth in a batch fermenter is represented by equation 5.55 written as ... 

Rapid quantification of products and substrates in a fermentation process is essential for process development and optimization. Most fermentation laboratories have access to HPLC equipment with possibilities to couple them to quite inexpensive diode-array-detectors, and this equipment could be used for quantitative monitoring of the process. Because HPLC can allow multi-component analyses, i.e., several analytes in the same sample can be determined virtually simultaneously, and since it is often necessary to monitor more than one substance at a time, this technique is an important tool for bioprocess monitoring. HPLC coupled to expensive MS does not represent standard equipment at fermentation laboratories. Even if mass spectrometers are available, DAD is often sufficient for quantification because product concentrations are relatively high, so the MS could be used for other issues. In paper II the goal was to develop and validate a method for analytical quantification of both the product and the substrate to enable the proper characterization of the kinetics of the process i.e., the determination of the values of substrate conversion and product formation. 

Measurement of Xylose Isomerization Kinetics and Equilibrium All experiments were carried out at 34 °C in a volume of 25 ml in 50-ml shake flasks agitated at 130 rpm in an incubated shaker. Each experiment was conducted in duplicate. All experiments used 60 g/ 1 xylose, and unless otherwise noted, 5.2 g/1 of enzyme pellets (0.13 g) was used for each experiment. Buffered solutions used in making the isomerization media were 0.01 M Tris buffer (pHed to 7.5 using 0.01 M NaOH) and 0.05 M sodium citrate buffer (pHed to 4.5 using citric acid). The pH was measured at the beginning of the experiments but was not monitored throughout. We have observed a small drift in pH of less than 1 unit over the course of 48 hrs. Even with this drift, the pH of the bulk solution stayed within the range suitable for fermentation and well-below the pH optimum of XI (pH 7.5). In experiments with co-inunobilized pellets, urea concentration was 0,0.01, or 0.1 M. 

---