On the other hand, lipase is a proteolytic enzyme that catalyzes the hydrolysis, the breakdown of fats, of lipids into their constituents. So we see that in the mouth we initiate the actual chemical breakdown of not only carbohydrates, but also of fats. Now, proteins are not actually broken down inside our mouth so we increase the surface area via mechanical digestion but we do not actually chemically break down our proteins in the mouth. Now, special types of glands known as salivary glands secrete a substance of fluid known as saliva in our mouth. And saliva consists of many different things. Now, saliva consists predominantly of water.