Alejandra Hernández-Valencia, Jose R. Cascante-Alpízar and Jordi J. Bou
Department of Chemical Engineering, Universitat Politecnica de Catalunya, Spain
One of the main problems observed during the synthesis process of Polyglutamic acid (PGA) via aerobic liquid fermentation, is the inability to achieve high yields when working at high culture volumes. This could be due to the reduction of the oxygen transfer rate (OTR) as the culture volume increases.
The aim of this study is to propose two possible methods for dealing with the problem of low dissolve oxygen concentrations: increment the pressure inside the bioreactor and increasing the oxygen partial pressure in the reactor atmosphere.
The fermentations performed with Bacillus Licheniformis ATCC9945A, showed that the polymer production slightly increases with increasing the oxygen content in the atmosphere. Thus, as the air pressure increases, the PGA production increases until the maximum is reached (13.34 g PGA/l), at 2.03 bar absolute. On the other hand, as expected, fermentation under enriched O2 atmosphere also increases productivity, but not as high pressure experiments.
In addition, it has been found that the pressure also alters the enantiomeric composition of the polymer, since the PGA synthesized under these conditions is mainly formed by L enantiomer while, the one synthesized at atmospheric pressure, contains predominantly D enantiomer.
According to the obtained results, raising the pressure inside the reactor is a more effective way of growing the fermentation yield than increasing the oxygen proportion in the atmosphere, because of the highest PGA concentrations obtained.
Keywords: Polyglutamic acid, Bacillus Licheniformis, enantiomeric composition, high pressure fermentation, Oxygen transfer rate.