pepsin assay:99% grade:usp/bp/ep packing:20kgs A proteolytic enzyme found in the gastric juice of mammals, birds, reptiles, and fish. It is formed from a precursor, pepsinogen, which is found in the stomach mucosa. Pepsinogen is converted to pepsin either by hydrochloric acid, naturally present in the stomach, or by pepsin itself. See also Enzyme. Pepsin is prepared commercially from the glandular layer of fresh hog stomachs. It is a part of the crude preparation known as rennet, which is used to curdle milk in preparation for cheese manufacture. Pepsin is also used for a variety of other applications in food manufacturing; to modify soy protein and gelatin, thereby providing whipping qualities; to modify vegetable proteins for use in nondairy snack items; to make precooked cereals into instant hot cereals; and to prepare animal and vegetable protein hydrolysates for use in flavoring foods and beverages.