Review Metabolism of lactate and sugars by dairy propionibacteria: A review

Abstract- Dairy propionibacteria are important organisms for the manufacture of Swiss-type cheese, for the biological production of propionate and vitamin 812 and have probiotic properties. In ail the se applications, their metabolic activities play a critical role. A complete understanding of propionate fermentation and of the metabolic routes used is therefore necessary. Dairy propioni-bacteria have a complex metabolism and involves several cycles. Lactate or sugars utilisation yields pyruvate which can be reduced to produce propionate via the transcarboxylase cycles, or oxidised to yield acetate and CO2 • During the coupled oxidation-reduction, ATP is produced by an electron transport system and fumarate acts as the final acceptor. Although propionibacteria are mainly anaer-obes, the electron transport system can be used in the presence of oxygen and they possess the citrate cycle, but can not grow under normal atmospheric oxygen pressure. The proportions of propionate acetate and CO2 produced vary depending on the strain used and this can be explained, to sorne extent, by their relative ability to utilise pyruvate via reactions of the citrate cycle. The physico-chemical environ ment during growth affects propionic acid fermentation; it is impaired by the pres-ence of oxygen and nitrate, but fermentation at acidic pHs enhances propionate production. Fer-mentation in presence of more than one substrate is complex and still poorly understood. When bot