How might I break down bread into glucose in a model of the human digestive system?

Generally speaking and as suggested by Rory, mechanical force probably plays a role in most instances (crustless bread may be different):

http://www.modelgut.com/dmg.html

I was hoping to post more about this but the websites of one of the institutes involved in developing the model gut doesn't provide much accessible information on first read.

Maybe this still gives you something of a starting point:

http://www.ifr.ac.uk/info/about/index.htm