Fermentable and non‐fermentable sugars: A simple experiment of anaerobic metabolism

The main objective of this class experiment is to show the time‐dependent consumption of a fermentable sugar (glucose) in the presence and absence of a non‐fermentable sugar (xylose) by bacteria in anaerobic conditions. The observation of the pH decrease due to acid production and the turbidity increase as a result of cell multiplication, both in function of time, enables an interesting discussion regarding the metabolic pathways and the products of anaerobic fermentation of carbohydrates. Also the time‐dependent disappearance of glucose due to its metabolic consumption is compared with the non‐disappearance of xylose and permits a discussion of the function of glycolysis and pentose phosphate pathways as metabolic routes. This work was supported by the Universidade de Uberaba, Fundaçao de Amparo à Pesquisa do Estado de São Paulo, and Conselho Nacional de Pesquisas (Brazil).