digestive system - What is an simple way to burn glucose for visible effect?

I want to make a partially working model of the digestive system that could digest complex carbohydrates. My ultimate goal is to be able to cut up some bread, put it into the model, operate it, and eventually see some effect equivelent to glucose being used in a muscle. I obviously have a very limited buget. How could I simulate glucose being burned in some way that has a visible effect?

Edit: I'm specifically looking for some way glucose can be used to achieve some visible effect that makes sense as a metaphor for combustion, without dangerous/expensive chemicals.