This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Gelatin has been used extensively for experimental work in studying the reactions of colloidal substances, particularly in connection with gel formation.
Uses of gelatin in foods. In food preparation gelatin is used as a basis to make a flavored gel for salads and desserts. It is used as an emulsifying agent, to form a basis for some types of candy like marshmallows, and it is used in frozen desserts.
Source of gelatin. Gelatin is obtained from collagen by hydrolysis. Collagen is a protein and is found in connective tissue, tendons, cartilage, in the organic part of bone tissue, in the inner layer of skin of animals, and in fish skins, scales, and "sounds" or fish bladders. Collagen is not found as a pure substance in these tissues, but in combination with inorganic materials and with other proteins like elastin, mucin, mucoid, etc. White connective tissue is found between the muscle fibers, in tendons, and in the inner layers of skin. It contains a high percentage of collagen. The jellying of meat broth after cooling is due to the gelatin, which has been formed from the collagen of the connective tissue. Sometimes the concentration of the gelatin in the broth is not great enough to bring about the formation of a gel. When pieces of baked fish skins are allowed to cool on the baking pan, they adhere to it quite tenaciously, because of the adhesive quality of the gelatin or glue formed from the collagen of the fish skin.