Starch absorbance

The starch grains are insoluble in water at room temperature. At 50-60 °C, starch absorbs water reversibly and hydrogen bonding is reduced. Above 60 °C (this temperature depends on the native source) the structure of the starch is modified irreversibly, crystallinity disappears and gelatinisation occurs. 

Since it contains many -OH groups in its structure, starch absorbs moisture well. When starch is heated with a dilute acid, it undergoes a hydrolysis reaction resulting in glucose as the final product. 

Potato starch or rice starch is generally used as a component of cutaneous powders and pastes with a high amount of solids. Starch absorbs a high percentage of water. As a result it swells. This may lead to the formation of a cmst on wounds. It is therefore not suitable for acute exsudative skin disorders. 

Acrylonitrile has been grafted onto many polymeric systems. In particular, acrylonitrile grafting has been used to impart hydrophilic behavior to starch (143—145) and polymer fibers (146). Exceptional water absorption capabiUty results from the grafting of acrylonitrile to starch, and the use of 2-acrylamido-2-methylpropanesulfonic acid [15214-89-8] along with acrylonitrile for grafting results in copolymers that can absorb over 5000 times their weight of deionized water (147). 

Aerosol dry shampoos fill an important market for those unable to tolerate wet hair, such as the sick and infirm. These products are based on oil absorbing powders which include talc, starch, and/or clay. They can be sprayed onto hair and then bmshed off after absorbing soils from the hair. 

Etherification and esterification of hydroxyl groups produce derivatives, some of which are produced commercially. Derivatives may also be obtained by graft polymerization wherein free radicals, initiated on the starch backbone by ceric ion or irradiation, react with monomers such as vinyl or acrylyl derivatives. A number of such copolymers have been prepared and evaluated in extmsion processing (49). A starch—acrylonitrile graft copolymer has been patented (50) which rapidly absorbs many hundred times its weight in water and has potential appHcations in disposable diapers and medical suppHes. 

Molecular Interactions. Various polysaccharides readily associate with other substances, including bile acids and cholesterol, proteins, small organic molecules, inorganic salts, and ions. Anionic polysaccharides form salts and chelate complexes with cations some neutral polysaccharides form complexes with inorganic salts and some interactions are stmcture specific. Starch amylose and the linear branches of amylopectin form inclusion complexes with several classes of polar molecules, including fatty acids, glycerides, alcohols, esters, ketones, and iodine/iodide. The absorbed molecule occupies the cavity of the amylose helix, which has the capacity to expand somewhat to accommodate larger molecules. The starch—Hpid complex is important in food systems. Whether similar inclusion complexes can form with any of the dietary fiber components is not known. 

A range of preparative and semipreparative soft gel systems with an improved mechanical stability and thus the chance to run them with increased flow rates were tested for their potential on the separation of starch glucans. For each of these systems a Sephacryl S-200 precolumn proved to be a perfect shock absorber for sample application, improved reproducibility of separations, and increased lifetime of soft gel systems. 

Protein concentration can be determined by using method of Bradford,9 which utilises Pierce reagent 23200 (Pierce Chemical Company, Rockford, IL, USA) in combination with an acidic Coomassie Brilliant Blue G-20 solution to absorb at 595 nm when reagent binds to the protein. A 20 mg/1 bovine serum albumin (Pierce Chemical) solution was used as the standard. Starch concentration was measured by the orcinol method4,9-11 using synthetic starch as the reference. A yellow to orange colour is obtained and measured at 420 nm when orcinol reacts with carbohydrates. Absorbance is determined by spectrometry. 

If gelatine, or starch, etc., is placed in water, it absorbs the latter and produces a flabby mass. At the same time heat is evolved. This is supposed to result from the work done hy an unknown tension P, which tends to open out the structure of the colloid. 

Starch is the main thickener in gravies, sauces, and puddings. It absorbs water, and becomes a gel when cooked. As the starch swells up with water, the amylose leaches out, and the amylopectin forms the gel. Some starches have higher amylopectin content and make better gels than those containing large amounts of amylose. 

Because starches are so good at absorbing water and bulking up, they are important in the texture of many food products. They are often used as fat substitutes. 

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). 

The pentose phosphate pathway is an alternative route for the metabolism of glucose. It does not generate ATP but has two major functions (1) The formation of NADPH for synthesis of fatty acids and steroids and (2) the synthesis of ribose for nucleotide and nucleic acid formation. Glucose, fructose, and galactose are the main hexoses absorbed from the gastrointestinal tract, derived principally from dietary starch, sucrose, and lactose, respectively. Fructose and galactose are converted to glucose, mainly in the liver. 

In the Phadebas TM amylase test (72) (Pharmacia Labs) the substrate was a water insoluble cross-TTnked blue starch in tablet form which also contains some inert ingredients, sodium and potassium phosphate buffer salts and sodium chloride. This polymer was hydrolyzed by amylase into water soluble blue starch fragments. After centrifugation the absorbance of the blue supernatant was proportional to the activity of amylase present in the test samples. The day to day variation on a quality control serum had a coefficient of variation of 2.7% based on 30 days of data in our laboratory. The method is simple, reproducible and uses microquantities of serum. 

With few exceptions, small particles of vegetable foods are generally stripped of their more accessible nutrients during digestion in the GI tract. In this way starch, protein, fat and water-soluble small components (sugars, minerals) are usually well absorbed. This is not always the case, however, for larger food particles or for molecules that cannot diffuse out of the celF tissue. Neither is it the case for the lipid-soluble components. These need to be dissolved in lipid before they can be physically removed from the cell to the absorptive surface, since the cell wall is unlikely to be permeable to lipid emulsions or micelles, and the presence of lipases will strip away the solvating lipid. 

Feedstuffs consist largely of complex polymers (e.g. proteins, starches, fats) that must be hydrolyzed to the constituent building blocks before they can be absorbed and made available to the host. The digestibility of many plant proteins is inherently lower compared to proteins from animal tissues. This is particularly true for the structural proteins (Carbonaro et al, 2000 Mariotti et al, 1999). As a consequence, amino acid scores for many plant proteins often do not reflect true availability to the host (Mariotti et al, 2001). 

Because plants present chlorophylls and carotenoids simultaneously, it may be useful to separate both groups from each other in a laboratory or preparative scale in order to avoid contamination in further purification steps, mainly when they are prepared in large amounts. Clean-up procedures using an open column packed with absorbents such as alumina, magnesia, polyethylene powder, powdered sucrose, DEAE-Sepharose, starch, cellulose, or MgO HyfloSupercel are good approaches. MgO HyfloSupercel in a proportion of 1 1 or 1 2 is the usual adsorbent. Sucrose and cellulose are interesting as they do not alter the chlorophylls, but they are tedious to work with. 

As a generalization, to be orally well absorbed a compound must be soluble in the contents of the gastrointestinal lumen [4]. Solubility in aqueous buffer is commonly used as a simpHfying surrogate for intestinal content solubility. There are rare exceptions to the principle that to be absorbed a compound must be soluble. SoHd particles, e.g. starch, can be absorbed. Absorption of very small quantities of even biologically very large compounds can occur via lymphoid tissue, e.g. orally active vaccines. Very hpophihc basic compounds, e.g. certain antimalarials, can be absorbed via the intestinal lymphatics and dehvered directly to the heart... 

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