The proton extrusion of growing yeast cultures as an on‐line parameter in fermentation processes: Quantitative determination of growth from milligram amounts of substrate in a minimized fed‐batch fermentation apparatus

The proton extrusion of growing yeast cultures was demonstrated to be a very exact and reliable on‐line parameter for the description of the growth of yeasts and substrate consumption in batch fermentation processes. Using this parameter we were able to build up a minimized fermentation apparatus (working volume about 90 ml) which permits the description of growth from substrate amounts of 5 to 50 mg quantitatively in fed‐batch fermentation processes. Using various yeast strains it was demonstrated for nitrogen‐free carbon sources such as hydrocarbons and carbohydrates that 1. the course of the proton extrusion indicates qualitatively whether any given carbon source can be utilized as a growth substrate or not, and that 2. the amount of proton extrusion is a reliable and reproducible quantitative parameter for growth on the tested substrate. This minimized fermentation apparatus offers advantages and possibilities to detect growth of microorganisms from very small substrate amounts in submerged cultures.