Starch 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. 

FIGURE 2.48 Change of plasma glucose concentration after meals of boiled wheat (A) and cassava ( ) starch. These data demonstrate a dramatic increase in plasma glucose levels 1 hr after the meal. These results are consistent with the fact that imcooked starch resists digestion in the small intestine. (Redrawn with permission from Bomet et al, 1989.)... 

B. Lactose and sucrose are digested by disaccharidases on the brush border of intestinal epithelial cells. Starch is digested by salivary and pancreatic amylase. Therefore, its digestion would be less affected by a lack of pancreatic juice than fat, which is digested mainly by pan-creatic lipase. A common finding in cystic fibrosis is steatorrhea (fatty stools). 

Bednar, G.E. A.R, Patil S.M. Murray C.M. Grieshop N.R. Merchen G.C. Fahey, Jr. Starch and fiber fraction in selected food and feed ingredients affect their small intestinal digestibility and fermentability and their large bowel fermentability in vitro in a canine model. / Nutr. 2001, 131, 276-286. 

The effects of technological processes were quantified only for the dry matter, the degradability parameters (for nitrogen, dry matter and starch) and the true intestinal digestibility of undegraded proteins. These values, and the PDI and the AADI values derived from them, are therefore different between the processed and the unprocessed feed material. 

Resistant starch Defined as the sum of starch and products of starch degradation not absorbed in the small intestine by healthy individuals. Resistant starches not digested in the small intestine reach the colon, where they are readily fermented by naturally occurring microflora. One of the main acids produced by these microorganisms is butyric acid, which is believed to play a positive role in promoting colon health. Resistant starch is classified into four categories. 

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. 

Not all of the starch in a food ends up being digested. The starch that is not absorbed by the body is called resistant starch, and it is considered dietary fiber. It is also a source of nutrition for intestinal flora, which make important vitamins (and intestinal gas). 

Diabetic patients have reduced antioxidant defences and suffer from an increased risk of free radical-mediated diseases such as coronary heart disease. EC has a pronounced insulin-like effect on erythrocyte membrane-bound acetylcholinesterase in type II diabetic patients (Rizvi and Zaid, 2001). Tea polyphenols were shown to possess anti-diabetic activity and to be effective both in the prevention and treatment of diabetes (Choi et al, 1998 Yang et al, 1999). The main mechanism by which tea polyphenols appear to lower serum glucose levels is via the inhibition of the activity of the starch digesting enzyme, amylase. Tea inhibits both salivary and intestinal amylase, so that starch is broken down more slowly and the rise in serum glucose is thus reduced. In addition, tea may affect the intestinal absorption of glucose. 

MORAis M B, FESTE A, MILLER R G, LiFSCHiTZ c H (1996) Effect of resistant and digestible starch on intestinal absorption of calcium, iron, and zinc in infant pigs. Pediatr Res. 39 872-6. 

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. 

Ingestion of commercial preparations that contain digestion-resistant starches and bacteria (e.g. homolactic lactobacilli) increases volatile fatty acid formation in the colon. This provides more fuel for colonocytes it is claimed regular intake of these preparations improves intestinal function and hence mood, known sometimes as die feel good factor. 

Acarbose is an intestinal a-glucosidase inhibitor that delays digestion and absorption of starch and sucrose. It is used in diabetes mellitus and is contraindicated in inflammatory bowel disease. 

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... 

---