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.