Digestion of starches

In humans, as soon as the cooked starch enters the mouth, it encounters an a-amylase that is secreted in saliva. The salivary a-amylase acts on the starch at an optimum pH of 6.7 and 37°C. It catalyzes the hydrolysis of the a-1 4 glyco- 

Essentials of Carbohydrate Chemistry Springer-Verlag New York Inc. 1998 

65- a-dl-gluco pyrano syl maltopentaose (BB7) (resistant to a-amylase attack) 

In humans the D-glucose is actively transported across the small intestine wall into the blood stream. This blood glucose is converted into liver or muscle glyco- 

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Acarbose is a nonabsorbable a-glucosidase inhibitor which blocks the digestion of starch, sucrose, and maltose. The digestion of complex carbohydrates is delayed and occurs throughout the small intestine rather than in the upper part of the jejunum. Absorption of glucose and other monosaccharides is not affected. Acarbose is adrninistered orally three times a day and chewed with the first mouthful of food. 

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. 

Digestion of starch involves the hydrolysis of the bonds between the glucose molecules. Two classes of hydrolytic enzymes are required amylases and oligo- and di-saccharidases (Figure 4.5). The disaccharidases are also involved in hydrolysis of sucrose and lactose. 

Figure 4.5 Digestion of starch and saccharides. The three enzymes hydrolyse the bonds between the glucose molecules.

These herbs can be selected in cases of food accumulation. Moreover, they can be used to prevent food accumulation, which often happens when the Stomach-Qi stagnates. The first three substances are often used together as they aid digestion of starch, cereal, fat and protein-rich food. Lai FuZi can effectively regulate the Qi and remove phlegm in the intestines it aids the digestion of all types of food. 

Mai Ya (Hordei fructus germinatus) Aids the digestion of starch food ... 

Addition of alpha-amylase can improve the digestion of starch and addition of protease has been shown to improve the digestion of protein. 

The breakdown of food begins in the mouth as it is chewed. Chewing mixes saliva in the food. Saliva contains the enzyme amylase that begins the digestion of starch. Once chewed and swallowed, the food reaches the stomach, where the acid present... 

Multicomponent starchy foods such as cereals also become more digestible after irradiation, but noncarbohydrate components, particularly vitamins, undergo decomposition.230 However, another report shows that the in vivo digestibility of starch in irradiated food is decreased, along with some other side effects (such as reduced digestibility of lipids and proteins), after 8 months of feeding.231... 

The principal locations for digestion of starch in humans are the mouth, the lumen of the small intestine, and the brush border of the epithelial cells of the intestinal mucosa. Food is masticated in the mouth, forming a bolus ready for swallowing, while the salivary a-amylase attacks the hydrated starch. The enzyme breaks the starch at random intervals, hydrolyzing internal a-1,4 bonds (and not the a-1,6 bonds constituting the branching points). The a-amylase will not break the bonds nearest the nonreducing... 

The saccharidases present in the surface of the small intestine relevant to the digestion of starch and its components are ... 

Q14 Pancreatic enzyme preparations contain amylase, lipase and protease enzymes. These supplements are given by mouth and compensate for the reduced or absent pancreatic secretions they assist the digestion of starch, fat and protein. Since the enzymes may be inactivated by gastric acid, they are usually presented in a protected, enteric-coated form which is sprinkled directly on the food. 

Q6 Alpha-amylase (a-amylase) is concerned with the digestion of starch to disaccharides and other products in the gut. The salivary glands also produce a-amylase, the parotid glands producing the greatest amount. 

The digestibility of starch depends on source, physical condition, and food preparation. With the exception of lignin, dietary fibers may be partially or fully hydrolyzed by enzymes of the microflora present In the colon, iJome products arc absorbed into the bloodstream, but most serve as energy sources for the colono-cy tes. Specific dietary fibers can influence fecal bulk, the rate of passage of material through the intestines, and certain maladies such as constipation. 

Isolation, empirical formula of /3-dextrin ( cellu-losine ) from crude bacterial digest of starch Isolation of a- and -dextrine Isolation of Bacillus macerans Empirical formula of a-dextrins a-Dextrin series diamylose, tetraamylose, hexa-amylose -dextrin series triamylose, hexa-amylose a-diamylose ... 

In the intestine, pancreatic a-amylase continues the digestion of starch. 

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