Lactose intolerance usually occurs in adults and is associated with race. The bacterial digestion of lactose produces gases leading to symptoms of diarrhea, bloating, and abdominal cramps. The undigested lactose moves to the large intestine where bacteria are able to digest it. When people do not have enough of the enzyme lactase, lactose is not sufficiently broken down resulting in a condition called lactose intolerance. But the mechanical breakdown is ongoing-the strong peristaltic contractions of the stomach mix the carbohydrates into the more uniform mixture of chyme. (This is a good thing as more glucose in the mouth would lead to more tooth decay.) When carbohydrates reach the stomach no further chemical breakdown occurs because the amylase enzyme does not function in the acidic conditions of the stomach. Only about five percent of starches are broken down in the mouth. The increased concentration of maltose in the mouth that results from the mechanical and chemical breakdown of starches in whole grains is what enhances their sweetness. The salivary amylase breaks down amylose and amylopectin into smaller chains of glucose, called dextrins and maltose. This enzyme breaks the bonds between the monomeric sugar units of disaccharides, oligosaccharides, and starches. Saliva contains the enzyme, salivary amylase. The salivary glands in the oral cavity secrete saliva that coats the food particles. Chewing, also known as mastication, crumbles the carbohydrate foods into smaller and smaller pieces. The mechanical and chemical digestion of carbohydrates begins in the mouth.
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