Intensification of yeast production with microbubbles

Yeast requires and consumes a high amount of oxygen rapidly during growth. Maintaining yeast cultures under sufficient aeration, however, is a significant challenge in yeast propagation. Due to their high surface area, microbubbles are more efficient in mass transfer than coarse bubbles. The performance of an airlift loop bioreactor equipped with a fluidic oscillator generated microbubbles in yeast propagation is presented here. The approach is compared with a conventional bubble generation method that produces coarse bubbles. Dosing with microbubbles transferred more oxygen to the cultures, achieving non-zero dissolved O-2 levels and consequently, eliminating the starvation state of yeast in contrast to coarse bubble sparging. The average cell growth yield obtained under microbubble sparging reached 0.31 mg/h (+/- 0.02) while 0.22 mg/h (+/- 0.01) was recorded for cells grown with coarse bubbles during the log phase. The percent difference in average growth yield after 6 hours was 18%. Additionally, the use of microbubbles in yeast harvest from growth medium proved effective, yielding > 99% cell recovery. The result of this study is crucial for the biofuel industry but also, the food, nutraceutical and pharmaceutical industry for which end product purity is premium. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.