Yeast is a very potent source of supply of enzymes. An enzyme is produced by living cells, either animal or vegetable. When an enzyme is brought into relation with certain organic compounds, its action usually, though not always, tends to decompose them into simpler combinations without itself undergoing any change. An enzyme acts only in solution. Enzymes are sensitive to hat and pH. Yeast contains small amount of several enzymes including Protease, Lipase, Invertase, Maltase and Zymase. The important enzymes in yeast are Invertase, Maltase and Zymase.
Protease: The protease can soften flour proteins and therefore, it can cause great changes in the structure and properties of the dough. However, the Protease in normal healthy bakers yeast are intracellular enzymes meaning that they are not able to pass through the cell membrane.
Lipase: It seems to be intracellular and acts on the fats which it encounters within the yeast, especially during sporulation. These fats are the reserve products for the cell during the maturation of the reproductive spores. The Lipase of a few species of yeast is able to diffuse through the cell membrane.