Experience in using an ethanol sensor to control molasses feed-rates in baker's yeast production

Fed-batch cultivation of Saccharomyces cerevisiae on lignocellulosic hydrolyzate

“…The biomass yields obtained in the PI-controlled cultivations, however, were somewhat lower than to be hoped for, especially when hydrolyzate was used as growth medium. The basis for the PI-controller used in this work has previously been demonstrated in cultivations of molasses (Axelsson et al 1988). Unfortunately, the biomass yield was not reported and could not be calculated from the data given.…”

“…One principle which has been used for aerobic fed-batch control of S. cerevisiae with high yield is that of maintaining a low and constant ethanol concentration in the broth (Axelsson et al 1988;Noronha et al 1999;Cannizzaro et al 2004). If the flow rate is lower than the maximum respiratory sugar uptake, ethanol will be consumed, signalling that the flow rate can be increased.…”

“…Maintaining a constant ethanol concentration will therefore ensure an optimal feed-rate near the critical feed-rate. The principle has been shown for yeast cultivation on molasses (Axelsson et al 1988(Axelsson et al , 1984, where a simplified model of the dynamics from the feed rate to the ethanol concentration was derived by mass balances and used as a basis for the developed of the PID regulator. The regulator was subsequently used in cultivation of S. cerevisiae from molasses with a set-point concentration of 0.4 g ethanol/l A different kind of problem arises in cultivations where lignocellulosic hydrolyzate is the carbon source compared to a untoxic carbon source.…”

Monitoring of volatiles in alcoholic fermentations on molasses via a gas membrane sensor

“…Good results were obtained for alcoholic fermentation on synthetic medium, but discrepancies were observed when fermenting cane or grape juices, due to the presence of unidentified interfering volatile components. The same kind of system allowed Axelsson et al (1988) to control molasses feed rate in yeast production: in that case the presence of volatiles other than ethanol could be neglected.…”

Control of continuous fed-batch fermentation process using neural network based model predictive controller

“…But, this measurement does not give any indication as to how the glucose is channeled through different pathways. Ethanol concentration in the culture, which can be easily measured by gas chromatography, can also be used to observe the variations in the pathways [28,29]. The biomass concentration control in continuous baker's yeast fermentation was achieved with control of dissolved oxygen concentration by manipulating air flow rate [30] and substrate feed rate [31].…”