Sugars, intestinal digestion

Maltose (1) occurs as a breakdown product of the starches contained in malt ( malt sugar see p. 148) and as an intermediate in intestinal digestion. In maltose, the anomeric OH group of one glucose molecule has an a-glycosidic bond with C-4 in a second glucose residue. 

The a-glucosidase inhibitors, acarbose (Precose) and miglitol (Glyset), lower blood sugar by delaying die digestion of carbohydrates and absorption of carbohydrates in the intestine. 

Pectin, the substance that makes jellies and jams so jelly-like, can help lower blood cholesterol levels by forcing the body to make more bile acids. Pectin is a type of fiber, and like most fiber, pectin cannot be digested by the human body. Instead, the fiber moves slowly through the small intestines. When pectin encounters sugar and acid, its molecules trap water within its long chains, turning into a gel-like mass. This gel traps and eventually eliminates bile acids from the gut. When this happens, the body must make more bile acids, reducing the amount of cholesterol in the blood. 

Beaugerie L, Flourie B, Marteau P, Pellier P, Franchisseur C, Rambaud JC. Digestion and absorption in the human intestine of three sugar alcohols. Gastroenterology 1990 99 717-723. 

Suppose we start with a starch-rich meal, say one containing a lot of pasta or bread. The digestion of starches begins in the mouth. Saliva contains an enzyme, salivary amylase (aka ptyalin), which catalyzes the conversion of starch to simple sugars such as glucose. This process is completed in the small intestine under the influence of other enzymes in the amylase class. This completes the first phase of carbohydrate catabolism the conversion of complex, polymeric carbohydrates (e.g., starches) to their simple monomeric units, the sugars. 

Short-chain fatty acids are not important components in most human diets although small amounts are present in bovine milk and therefore in dairy produce. Nonetheless, they are an important fuel for cells of the colon (colono-cytes), since they are formed endogenously. The lumen of the colon contains a very large number of microorganisms, some of which can break down the polysaccharides that are not digested in the small intestine. The sugars that are produced are fermented to form the short-chain fatty... 

Polyols are frequently used sugar substitutes and are particularly suited to situations where their different sensory and functional properties are attractive. In addition to sweetness, some of the polyols have other useful properties. For example, although it contains the same number of calories/gram as other sweeteners, sorbitol is absorbed more slowly from the digestive tract than is sucrose. It is, therefore, useful in making foods intended for special diets. When consumed in large quantities (1-2 oz 25,059 g)/dav, sorbitol can have a laxative effect, apparently because of its comparatively slow intestinal absorption. 

The first stage of catabolism, digestion, takes place in the stomach and small intestine when bulk food is broken down into small molecules such as simple sugars, long-chain carboxylic acids (called fatty acids), and amino acids. In stage 2, these small molecules are further degraded in cells to yield two-carbon acetyl... 

Lactase An enzyme in the small intestines needed to digest lactose, a sugar found in milk. 

The small intestine continues the chemical digestion process started in the stomach with a focus on enzymatic cleavage of fats and sugars. Proteins, already partially broken down in the stomach, are cleaved into individual amino acids. Once different food types have been digested completely, they are ready for absorption. The small intestine consists of three regions duodenum, jejunum, and ileum (Table 3.5).5... 

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