Penicillin Fermentation

The success of fermentation processes often depends upon the maintenance of an environment sufficient in oxygen concentration so as not to limit or impair normal respiratory activity. Maintenance of such an environment is, in turn, largely dependent on the adequacy of oxygen transfer from air to the liquid medium. Of the possible pathways for oxygen transport, absorption into the medium and subsequent diffusion to the cells is undoubtedly the main one in submerged fermentation. Bartholomew et al. (1950b), Hixson and Gaden (1950), and Wise (1951) were the first to consider the mechanisms of oxygen transfer in fermentation systems, and they developed essentially identical methods for the quantitative expression of absorption rates. The absorption of oxygen into aqueous solutions, especially fermentation media, is generally considered as a liquid-film controlled mass-transfer operation. As such it should be expected that the mass-transfer rate, specifically the "oxygen absorption" rate for this case, is a function of those physical properties of the broth which affect interfacial area, turbulence, and boundary (film) conditions. Two such properties which undergo considerable change during many fermentations are surface tension and viscosity. For an excellent treatise on the subject of oxygen transfer in fermentations, the reader is referred to the recent review by Finn (1954). Apparently, no reports have been published of the changes in the rate of oxygen transfer which are due to physical property alterations of the broth as the fermentation progresses. Many fungal fermentations produce thick non-Newtonian3 broths as the mycelium