In the mouth of course, because you have to chew it ( mechincally) to have it go down easier
Chewing begins mechanical breakdown of food through mastication
The mechanical breakdown of food starts with the saliva in your mouth.
Saliva
Saliva
Mechanical Digestion
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the physical change in the change in food when the enters esophagus is when it has a chemical breakdown in your mouth with a mechanical breakdown the chemical breakdown is when your salivia is making the food moist the mechanical is when you chew the food so it easier for it to enter the esophagus and so the salivia can get it moist then your esophagus uses muscles to push the food down into your stomache
metabolism
The process begins when you chew, that is the first physical breakdown which happens alongwith chemical breakdown with the help of the saliva. the other happens in your stomach, where the food is broken down to form a semi liquid type of substance.
Pepsin begins the digetion of Protein. Pepsin is found in the stomach.
The stomach initiates the digestion of proteins.
There are two. Salivary amylase is an enzyme that begins the enzymatic breakdown of starches and lingual lipase which begins the enzymatic breakdown of lipids.