According to Branch Basics, digestion begins in the mouth when the process of chewing starts. Salivary glands will secrete a mucus, which assists in lubricating the food before swallowing.
Saliva consists of three enzymes: Amylase, Protease and Lipase. Amylase comes from the parotid gland and is used to break down carbohydrates. Protease comes from the submandibular glands and is used in the initial stages of protein digestion. Lipase comes from the sublingual glands found underneath the tongue to start fat digestion. Chewing is a very important part of digestion because the release of these three enzymes starts off the digestion process.