“Lactose Intolerance.” Last updated April 23, 2012. The National Digestive Diseases Information Clearing House states that African Americans, Hispanic Americans, American Indians, and Asian Americans have much higher incidences of lactose intolerance while those of northern European descent have the least.National Digestive Diseases Information Clearing House. 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. Once carbohydrates are chemically broken down into single sugar units they are then transported into the inside of intestinal cells. Maltase breaks the bond between the two glucose units of maltose, and lactase breaks the bond between galactose and glucose. Sucrase breaks sucrose into glucose and fructose molecules. These enzymes, known collectively as disaccharides, are sucrase, maltase, and lactase. Additionally, enzymes are secreted by the intestinal cells that line the villi. This pancreatic juice contains the enzyme, pancreatic amylase, which starts again the breakdown of dextrins into shorter and shorter carbohydrate chains. Upon entry of the chyme into the small intestine, the pancreas releases pancreatic juice through a duct. The chyme is gradually expelled into the upper part of the small intestine. But the mechanical breakdown is ongoing-the strong peristaltic contractions of the stomach mix the carbohydrates into the more uniform mixture of chyme.įigure 3.3.2: Salivary glands secrete salivary amylase, which begins the chemical breakdown of carbohydrates by breaking the bonds between monomeric sugar units. (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. Table 3.3.1: Sweetness Comparison of Carbohydrates Carbohydrate Whole-grain foods satisfy the body the entire way through the digestive tract and provide the nutrients that also better satisfy the body’s functional needs. Remember too that they contain fiber which makes elimination much smoother. Additionally, once in the stomach, whole-grain foods take longer to digest and keep you full longer. Whole grains take longer to chew and get sweeter the more you chew them. In a colloquial sense, we identify such people as having a “sweet tooth.” This does not mean that the less-sweet whole grains containing more starches and fiber are less satisfying. Sweetness is a pleasurable sensation and some people enjoy the taste more than others. See Table 3.3.1 for sweetness comparisons among different naturally-occurring carbohydrates. Whole grains provide satisfaction from the beginning to the end of the digestion process. Fructose is the top naturally occurring sugar in sweetness value.įigure 3.3.1: Blueberry pancakes. Sweetness varies between the different carbohydrate types-some are much sweeter than others. Even extremely low concentrations of sugars in foods will stimulate the sweetness taste sensation. Fast-releasing carbohydrates stimulate the sweetness taste sensation, which is the most sensitive of all taste sensations. Sweetness is one of the five basic taste sensations of foods and beverages and is sensed by protein receptors in cells of the taste buds. Discuss how carbohydrates are digested and absorbed in the human body.
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