The survival and activities of microorganisms depend on water availability. In this work, relationships expressing the dependence of oxygen solubility and oxygen transfer and uptake rates on water activity are considered. The special emphasis is given to the analysis of the effects of dissolved substance concentrations on solubility of gases. The effects of different dissolved salts, sugars and polyols are mentioned and discussed. More attention is given to experimental data and established relationships referring to the aerobic microbial conversion of D-sorbitol into L-sorbose. The proofs supporting the possibility to define the water activity on the basis of oxygen solubility are given by demonstrating them graphically and by mathematical equations
