The first nutrient to start breaking down in the cheeseburger will be the carbohydrate. Carbohydrates break down immediately when coming into contact with salivary amylase which is found in the mouth. Salivary amylase hydrolyzes the starch into an oligosaccharide. As the carbohydrate travels down the esophagus into the stomach the amylase becomes denatured by the low pH in the stomach. Once through the stomach it, passes into the small intestine where it comes into contact with Pancreatic Amylase that also converts starch into oligosaccharides and maltose (a double sugar). Enzymes called Dextrinase and Glucoamylase hydrolyze the oligosaccharides and Maltase hydrolyzes the maltose to glucose.
The second and third nutrients to be broken down and absorbed are the proteins and lipids. Once the proteins enter the stomach the enzyme Pepsin hydrolyze Tyresin-Phenyalenine (Tyr-Phe) peptide bonds, and breaking proteins into smaller polypeptides. Trypsin and Chymotyrpsin hydrolyze polypeptides into short oligopeptides in the small intestine because pepsin no longer works due to the high pH level. The oligopeptides become broken into amino acids by 3 brush border enzymes called Carboxypeptidase, Aminopeptidase, and Dipeptidase. Like protein, lipid break down doesn’t begin until entering the stomach. Lingual Lipase which comes from a salivary gland in the mouth does not activate until entering the low pH environment of the stomach. Fat hasn’t been