Starch digestion, human

Why is starch digestible by humans Why is cellulose not digestible by humans ... 

Lo Piparo E, Scheib H, Frei N, Williamson G, Grigorov M, Chou CJ. 2008. Flavonoids for controlling starch digestion Structural requirements for inhibiting human alpha-amylase. J Med Chem 51 3555-3561. 

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... 

Figures 2.47 and 2.48 show the effects of starch digestion and absorption on human subjects. In Figure 2.47, a meal consisting of 35 g raw wheat starch or cassava starch was consumed in a suspension of water Samples of blood, withdrawn at 30-minute intervals, were analyzed for plasma glucose. The data indicate slight increases in the plasma glucose levels wheat starch perhaps produced a...

The amylase inhibitor of navy beans is instable in the stomach and becomes active only after preincubation with the enzyme in the absence of starch. As a result, it has no measurable influence on the digestion of starch by human beings. Moreover, the average amounts of inhibitor ingested with the food are small compared to the amylase activity present. 

Englyst, H. N., and MacFarlan, G.T. 1986. Breakdown of resistant starch and readily digestible starch by human gut bacteria. J. Set FoodAgric. 37 699. 

Unlike many of the catalysts that chemists use in the laboratory, enzymes are usually specific in their action. Often, in tact, an enzyme will catalyze only a single reaction of a single compound, called the enzyme s substrate. For example, the enzyme amylase, found in the human digestive tract, catalyzes only the hydrolysis of starch to yield glucose cellulose and other polysaccharides are untouched by amylase. 

It has recently been reported that a fraction of food starch, named resistant starch (Asp and others 1996), is not digestible by humans. Nowadays resistant starch is considered a DF constituent and is a major constituent of IDF in starchy foods. However, resistant starch is absent in most fruits and vegetables, with the exception of bananas, which contain more than 15% dry weight when the fruit is unripe (Gofii and others 1996). 

Dietary fibre was defined by Hugh TroweU as the plant polysaccharides and lignin which are resistant to hydrolysis by the digestive enzymes of humans . This definition lacks chemical precision, because non-flbrous pectins and gums are also present. The term nonstarch polysaccharide (NSP) is often preferred, although the term dietary fibre still persists. Unfortunately, NSP is also not satisfactory since some starch, known as resistant or par-... 

HV196 Livesey G., J. A. Wilkinson, M. Roe, et al. Influence of the physical form of barley grain on the digestion of its starch in the human small intestine and implications for health. Am J Clin Nutr 1995 61(1) 75-81. HV207... 

---