The hemicellulase enzyme breaks down hemicellulose, which is a type of cellulose and a key component of the cell wall in all plants. Different forms of plant hemicellulose include glucans, galactans, xylans, mannans and pentosans. Common fiber-rich breakfast cereals, for example, have a large amount of hemicelluloses (2 to 12%). Hemicellulase is needed to break down these fiber-rich components, and because it is not produced naturally in the human body, we rely on microorganisms that live in the human digestive tract to produce it for us.