Citric acid is a primary metabolite of the citric acid cycle and is present in small amounts in all animals and plants. It was first commercially produced in England in 1826 by extraction from lemons. From 1919 onwards, industrial production using the fungus Aspergillus niger became established – a process that still dominates the market today. Today, over 80% of citric acid worldwide is produced biotechnologically. Its main area of application is in the food industry, for example as an acidifier or preservative. Despite its success, the use of A. niger poses some problems: the fungus can produce mycotoxins such as ochratoxin A. Cultivation is challenging because it requires a narrow pH window and a precisely balanced nutrient composition.
The yeast Yarrowia lipolytica could offer an interesting alternative here. It is much more flexible in terms of the substrates used: even glycerin, which is often produced as an industrial by-product, can be used as a carbon source. In addition, the yeast is considered non-pathogenic and does not form any toxic by-products.
The TU Braunschweig team Squeeze the Yeast, with their team leader Anwar Walid, doctoral student at the Institute of Bioprocess Engineering at TU Braunschweig, and the eight students Lukas Blasczyk, Niklas Ebert, Jannik Ellermann, Maximilian Müller, Sammy Leon Singh, Jannis Schweizer, Tabea Tiedmann, and Tanja Zierott, took on the challenging task.
After the design and construction phase and preparatory cultivation, the Braunschweig team traveled to TU Dresden. Upon arrival and after a brief introduction to the TU Dresden laboratories, the 12 (!) participating teams had time to set up and prepare their bioreactors. The 24-hour cultivation process began with the inoculation of the reactors with the inoculum. From this point on (t = 0), the bioreactor had to function autonomously.
Squeeze the Yeast got off to a good start, but with a final citrate concentration of 1.2 g/L citrate, it narrowly missed the podium by a margin of 0.1 g/L citrate.
The €99 competition is an exciting and challenging contest in which students can demonstrate their theoretical knowledge in a very practical scenario. Participants are required to demonstrate not only skills in reactor design and construction, but also in the optimization of cultivation conditions and compliance with economic constraints.
The preparation and preliminary work carried out by the biotech team at TU Braunschweig was kindly supported by study quality funds from the Faculty of Life Sciences and by the provision of premises and materials by the Institute of Bioprocess Engineering and the Institute of Microbiology.
This year's team is looking forward to presenting their project at the next mentor evening to anyone interested in participating in the next competition and to supporting them with expert advice.