Respiratory quotient control

Control of microaerobic fermentations by oxygen transfer rate has limitations, as the distribution of oxygen may differ in various types and sizes of reactors. In a somewhat different approach, control by respiratory quotient was attempted. Optimum 2,3-BD production was seen at a respiratory quotient between 4.0 and 4.5, and product concentration (butanediol and acetoin) greater than 100 g/1 was measured. This was compared to a control fermentation where an oxygen transfer rate of 35 mmol/l/h was maintained. In this case, the respiratory quotient eventually decreased to about 1.5 and product formation was only about 85 g/1. Biomass in the fermentation with respiratory quotient control was higher than in the OTR-controlled fermentation (Zeng et al. 1994a). 

Amitrole had a drastic effect on the fixation of 14C02 by illuminated chloroplasts of Chlorella pyrenaidom, lowering the incorporation into sucrose by 95% at a concentration of 500 mg. per liter it did pot affect phosphorylated compounds.145 Carbohydrates hydrolyzable by acids were higher (51%) in treated, chlorotic corn leaves than in controls (32%), and this result was interpreted as due to increased metabolism of proteins and fats. The respiratory quotient of 0.8 to 0.88, compared to controls near 1.0, supported this interpretation.145... 

In plant cell cultures, shake flask culture is an indispensable stage of cultivation. Investigations in a shake flask are very essential and critical to bioprocess scale-up and optimization. We have developed a simple and convenient technique based on the principle of the Warburg manometric method to measure 02 uptake rate (OUR) and C02 evolution rate (CER) of suspended cells in a shake flask culture. This technique has been successfully applied to suspension cultures of Panax notoginseng cells, and some important bioprocess parameters, such as OUR, CER, respiratory quotient (RQ), SOUR and specific CER (SCER), were quantitatively obtained [99]. As long as the environment temperature is strictly controlled to within an error of 0.1 °C, the measuring system is accurate and reproducible, is easy to operate, is economical, and is also able to treat many samples simultaneously. 

The key components for process monitoring were selected according to these data and some additional information. The in situ monitoring of the DO as well as the oxygen and carbon dioxide concentrations in the off gas allowed the evaluation of the oxygen transfer rate (OTR), the C02 production rate (CPR) and the respiratory quotient (RQ). The control of the pH-value and the DO was the prerequisite for the maintenance of the optimal growth and product formation conditions. 

In both cases the accuracy requirement is shifted from the sensors to the oxygen dosage or constant-flow generator. Processing the respiratory quotient, RQ, requires inaccuracies of oxygen uptake and CO2 production of less than 3% to result in RQ values with deviations of less than 6-8170, which can be used to control the nutrition of patients in the post-operation phase. To complete the parameters needed, the nitrogen excretion has to be determined by clinical laboratory methods. 

In man the respiratory factors are usually not markedly changed by morphine. In resting healthy individuals minute volume may be decreased 10-15% and respiratory rate may be unmodified or increased. Oxygen consumption decreases 8-10%. Alveolar carbon dioxide tension increases 2-3 mm. and the blood carbon dioxide capacity remains within 4 vol. % of the control value. The response to carbon dioxide in the inspired air is decreased and the blood remains neutral or shifts 0.05 pH toward the acid side, but experiments are recorded also where respiratory minute volume and oxygen consumption increase and all authors are concordant with respect to a low respiratory quotient after morphine. 

Whole room calorimetry is considered the gold standard for measuring energy expenditure in humans. Although the subject is free to move around in the calorimetric chamber, spontaneous physical activity is greatly reduced. Furthermore, the measurement is carried out under strictly controlled, artificial environmental conditions and often is of short duration (<24 hr). However, indirect calorimetry does provide important information about the basal metabolic rate, respiratory quotient, sedentary energy expenditure, and sleeping metabolic rate. 

Fig. 23.2 Energy expenditure and substrate oxidation. Data are presented as means SD. Indirect calorimetry was measured after a 10-h overnight fast. LCHAD-defident patients (n = 9 closed bars and closed circles) have a similar resting energy expenditure as control subjects (n = 9 white bars and open squares) expressed as mean kcal/day (a) or kcal/kg of fat-free mass (b). Resting respiratory quotient was significantly higher in the LCHAD-deficient patients (n = 9 gray box plot)...

Randolph et al. [78] developed a control strategy based on the estimation of the respiratory quotient of S. cerevisiae from heat flow rate measurements and rcoj In fact, the oxygen consumption rate can be estimated from and the oxycaloric quotient, Qo, since almost all the heat released is due to the... 

Figure 31 Estimation of the Respiratory Quotient from heat flow rate and CO, evolution rate during controlled fed-batch cultivation for different values of the controller gain. A, B, and C correspond to values of the controller gain of 1.23, 0.85 and 0.45, respectively. (Reproduced from Reference [78] with permission of the author and publisher).

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