9 - Fermentation

Abstract

This chapter provides an overview of fermentation process. The word fermentation has undergone many changes in meaning during the past hundred years. With the recognition of fermentation as an anaerobic process, parallels were drawn between the biochemistry of microorganisms and that of mammalian tissues. Because the intermediates of the metabolism of glucose were found to be the same, it was postulated that all fermentation processes must follow similar paths. Consequently, the microbial fermentation of carbohydrates was considered to be similar to mammalian glycolysis. It was found that fermentative bacteria may dispense with the use of their cytochromes under anaerobic conditions, for their phosphorylation processes are substrate phosphorylation in which the electron donor is an organic substrate that transfers its electrons to an NAD+ or NADP+ system. The amount of NAD+ in microorganisms, however, is limited and NAD+ must therefore be regenerated if metabolism is to continue. Under anaerobic conditions, this regeneration can be accomplished by an oxidation–reduction mechanism involving pyruvate or other compounds derived from pyruvate. These reactions from pyruvate can vary considerably among microorganisms and, therefore, lead to the formation of characteristic end products that are used in bacterial classification.