Investigation and control of fermentation processes using fermenter calorimetry

Abstract

It is well known, that heat generation and total metabolic activity in biological systems are strongly correlated. Thus the heat production can provide important information for the study, supervision and control of biological fermentations. Microcalorimeters are widely used for studies concerning physiology, ecology, and pharmacology. They are very sensitive, but the measuring principle exhibits methodical disadvantages for its application in biotechnology (direct control of the fermentation inside of the measuring cell and sampling is impossible). Reaction calorimeters used in chemistry are too insensitive for the detection of small changes in heat generation. Therefore, we developed a new isothermal heat-flux calorimeter-fermenter with a working volume of 2l. The detection level for heat generating processes is 10 mW/l under standard fermenting conditions including agitation, aeration and pH-control. In situ sterilization of the apparatus can be handled easily. The calorimeter is thought to be a versatile tool for laboratory optimization of a fermentation. The aim of the presented work is to discuss what results have been obtained so far and how the heat signal can be used advantangeously in biotechnology.