Experimental simulation of oxygen profiles and their influence on baker's yeast production: I. One‐fermentor system

In production‐scale bioreactors microorganisms are exposed to a continually changing environment. This may cause loss of viability, reduction of the yield of biomass or desired metabolites, and an increase in the formation of by‐products. In fed‐batch production of baker's yeast, profiles may occur in substrate and oxygen concentrations and in pH. This article deals with the influence of a periodically changing oxygen concentration on the growth of baker's yeast in a continuous culture. Also, influences on the production of ethanol, glycerol, acetic acid, and on the composition of the cells were investigated. It was found that relatively fast fluctuations between oxygen‐unlimited and oxygen‐limited conditions with a frequency of 1 or 2 min had a distinct influence on the biomass and metabolite production. However, RNA, protein, and carbohydrate contents measured in cells exposed to fluctuations differed little from those in cells from an oxygen‐unlimited or an oxygen‐limited culture. The respiration and fermentation capacities of cells exposed to fluctuations can be larger than the capacities of cells grown under oxygen‐unlimited conditions.