Starch digestive activity

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. 

Specific Diffusion-based Limitations to Decay. If microbial colonization is confined to the surface of materials, the decay rate will inevitably be lower than seen where proximity between substrate and microbial cells is possible because enzymes produced by the cell and soluble products formed by enzymatic attack must diffuse a considerable distance. For example, if closer contact between the starch face and fungus were possible than seen in Figure 2, uptake of starch digestion products would occur at the growing tip and translocation within the mycelium by active transport would be possible. This... 

Protein and starch digestion, on the other hand, have potent nonpancreatic compensatory mechanisms. Due to the compensatory action of salivary amylase and brush border oligosaccharidases, a substantial proportion of starch digestion can be achieved without pancreatic amylase. Similarly, protein denaturation and hydrolysis is initiated by gastric proteolytic activity (acid and pepsin) and continued by intestinal brush border peptidases, and is thus partly maintained even in the absence of pancreatic proteolytic activity. 

The subcellular localization of the starch biosynthetic and degradative enzymes of spinach leaves was carried out by measuring the distribution of the enzymes in a crude chloroplast pellet and in separated components of a protoplast lysate. The enzymes which were involved in the syntheses of starch were detected in the chloroplasts, whereas some of the enzymes involved in the degradation of starch were mainly in the soluble protein fraction but were also found in the chloroplast. The digestion pattern of the amylase on amylopectin as substrate indicated that the enzyme was an a-amylase from its endo-lytic activity, but displayed properties unlike the typical a-amylase isolated from endosperm tissue. A time-sequence analysis of the starch digestion pattern in germinating... 

Enzyme Assays. Starch digestion from blends by porcine a-amylase (Sigma) was determined by measuring soluble product formation by the phenol-sulfuric acid method (12). Incubations were conducted in 20 mL of 0.05 M phosphate buffer (pH 7.0) containing 8 pieces of 1 x 2 cm starch-plastic blend and 2 /iL mL merthiolate to inhibit microbial catabolism of digestion products (13). Merthiolate did not inhibit en2yme activity or interfere with product assays. Sufficient enzyme was added to give a 100 to 200 units mL solution. Incubation temperature was 35° C. Mixtures were shaken at 50 to 70 rpm on a rotary shaker. 

Based on the mechanisms of enzyme hydrolysis of starch and the diffusion processes of enzyme and the starch digestion products in the plastic matrix, the following assumptions were made (a) the diffusion of both the enzyme and the products in the plastic matrix obeys the Pick s first law, (b) the diffusion coefficient is constant throughout the matrix during the reaction, (c) the hydrolytic reactions take place only inside the hydrophobic plastic matrix, and (d) the reaction between the enzyme and the substrate is a modified Michaelis-Menten type and the product (P), will competitively inhibit the enzyme activity ... 

A now somewhat dated form in which urinary amylase activity can be expressed. It is defined as the number of millilitres of 0.1% starch digested by 1 ml of urine at 37 °C in thirty minutes. 

Iodine Test Iodine forms a dark blue complex with starch molecules made up of at least six dextrose residues. Amylolytic activity is assayed by incubating starch with the enzyme under specific conditions. Iodine is then added to the reaction medium. The loss of color intensity due to the degradation is related to the extent of starch digestion and thus to the enzyme concentration. The method is rapid and inexpensive, but not accurate [32]. The KNU is the amount of enzyme that breaks down 5.26 g starch [47] per hour, at 37°C and pH 5.6, in the presence of 3 X 10 mol Ca /L. 

Intestinal processes studied with C02 breath tests are carbohydrate (lactose and starch) digestion (lactase and a-amylase activity), lipid digestion (lipase activity), protein digestion (trypsin activity), sugar absorption, fatty acid absorption, small intestinal bacterial overgrowth, oro-cecal transit time. The substrates used are indicated in Table 6. 

LONGSTAFF M, MCNAB J M (1991) The inhibitory effects of hull polysaccharides and tannins of field beans (Vida faba L.) on the digestion of amino acids, starch and hpid and on digestive enzyme activities in young chicks. Br. TNutr. 65 199-216. 

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