A giant bowl of ‘pancake dough’ is the investigation area of fermentation scientists. How to get the highest yield, in a cost-effective way, from this biotechnological production engine that is a fermenter?
Part of the scientists’ task is to establish what goes in and what comes out. Although the number of parameters is limited, the apparent simplicity is deceptive. “It is not just getting the numbers right. It mainly comes down to physiological insight, to understand the natural behavior. Managing the unpredictability of micro-organisms captivates me already for decades”, says Principal Scientist Fermentation Sybe Hartmans.
“As a fermentation scientist”, Hartmans says jokingly, “I consider myself a microbiologist with bookkeeping skills.” He refers to making mass balances; the water and sugar that go into the fermenter tank should exactly match the output in product yield, water evaporation and so forth. “Basically, fermentation is a process with only a limited number of parameters to influence”, Hartmans admits. “You have the medium, the sugar influx and the micro-organisms. These produce a volume that varies according to oxygen availability, temperature, pH and growth rate. On a large scale the technological aspects of mixing result in all kinds of gradients that influence the productivity of the micro-organism. But what really fascinates Hartmans and what’s vital in fermentation is the physiology of the micro-organism. “The process is simple, but the vast complexity of the micro-organism as one of its parameters makes up for that. The micro-organism’s behavior, influenced by external conditions, is still a riddle. For example, when you cut the sugar influx, behavior changes. To shed light on that enigma is what drives me.” Hartmans already got hooked during his study Food Technology in Wageningen. “Initially I would specialize in chemistry, but I chose for a PhD in microbiology instead, because the tiny living creatures fascinate me.”
As a fermentation scientist, Hartmans collaborates closely with strain developers. “They develop the best producing organisms for our processes, often by introducing new genes. During this process, these new genes can cause all sorts of unpredictable behavioral changes . They can for instance influence the branching of fungi: the less threads they create, the lower the viscosity and the better oxygen can be transferred. But how do you induce a fungus to behave like a yeast that can grow to up to 150 grams of dry matter per liter? It is as yet unknown what strings to pull for that.”
Strains are usually initially selected by measuring their product formation capabilities in a micro titer plate. Hartmans: “This compares to selecting sprinters to run the marathon of production. You end up with the sporty types, but not necessarily with the best marathon runner. Therefore we have, together with our strain developers, adjusted the micro titer plate test conditions. To simulate operational conditions we’ve introduced a slow sugar release system to identify the endurance performers among the strains.”
Smaller vessel, bigger steps
Better strains and improved fermentation conditions boost the yield of enzyme production by 7% annually. To keep up this pace, the fermentation experts have to keep up with the accelerating strain selection. Sometimes the fermentation performance of a hundred new strains has to be established simultaneously. Hartmans: “Before, we used twenty liter vessels, but experience and more sensitive equipment enable us to use smaller ones. From a hundred strains in one milliliter micro titers we move to testing the top eight in one liter vessels and only the two best performing strains in twenty liter ones as a last step before large scale implementation.”
“Thanks to these technological developments and miniaturization, it will be possible to master the operational conditions in micro titer plates, says Hartmans. “The next step is to bring under control parameters like the sugar concentration and the pH, on the micro titer plate level, and to do this at the same time.”
In production, there is a trend to move from stirred-tank fermenters to the entirely different bubble-column design. In a bubble column, the agitator and the heat producing engine are replaced by air bubbles that can do the mixing and oxygen transfer at lower investment costs, maintenance and operational costs. Hartmans: “Experience and insight have enabled us to minimize or even skip the time-consuming pilot plant scale and to go directly from lab-scale to production scales of more than 200 m3.”