Human digestive system in the small intestine. Water and minerals are reabsorbed back into the blood in the colon of the large intestine, where the environment is slightly acidic. Some vitamins, such as biotin and vitamin K produced by bacteria in the gut flora of the colon are also absorbed. The parietal cells in the fundus of the stomach, produce a glycoprotein called intrinsic factor which is essential for the absorption of vitamin B12. Vitamin B12 (cobalamin), is carried to, and through the stomach, bound to a glycoprotein secreted by the salivary glands - transcobalamin I also called haptocorrin, which protects the acid-sensitive
Digestive biscuit packs sold annually. Digestives are also popular in food preparation for making into bases for cheesecakes and similar desserts. Chocolate digestive biscuits are also available, coated on the underside with milk, dark or white chocolate. Originally produced by McVitie's in 1925 in the UK as the Chocolate Homewheat Digestive, other varieties include the basic biscuit with chocolate shavings throughout (chocolate "chips" in the biscuit mix), or a layer of caramel, mint chocolate, orange-flavoured chocolate, or plain chocolate. American travel writer Bill Bryson described the chocolate digestive as "a British masterpiece". The McVitie's chocolate digestive is the most popular biscuit in