Starch, examples

Biochemical degradation of plastics is another possible approach. It is realized by addition of organometallic compounds or starch. Examples of applications include the mulch films widely used in agriculture, made of polyethylene or PVC. These films rot within one vegetation period and can be plowed under. 

Many compounds can be produced organically from petroleum, or produced biochemically from biological raw materials. For example, ethanol is regularly produced by catalyzed gas-phase hydrogenation of ethylene, Example 12.4, and also produced biochemically from sugar (or starch). Example 16.1. The resulting ethanol is the same from either source (except in the eyes of the US laws that subsidize com-based ethanol motor fuels but not hydrocarbon-based ethanol.)... 

A few substances indicate the presence of a specific oxidized or reduced species. Starch, for example, forms a dark blue complex with 13 and can be used to signal the presence of excess 13 (color change colorless to blue), or the completion of a reaction in which 13 is consumed (color change blue to colorless). Another example of a specific indicator is thiocyanate, which forms a soluble red-colored complex, Fe(SCN) +, with Fe +. 

Dichromated Resists. The first compositions widely used as photoresists combine a photosensitive dichromate salt (usually ammonium dichromate) with a water-soluble polymer of biologic origin such as gelatin, egg albumin (proteins), or gum arabic (a starch). Later, synthetic polymers such as poly(vinyl alcohol) also were used (11,12). Irradiation with uv light (X in the range of 360—380 nm using, for example, a carbon arc lamp) leads to photoinitiated oxidation of the polymer and reduction of dichromate to Ct(III). The photoinduced chemistry renders exposed areas insoluble in aqueous developing solutions. The photochemical mechanism of dichromate sensitization of PVA (summarized in Fig. 3) has been studied in detail (13). 

Many of these reactions are reversible, and for the stronger nucleophiles they usually proceed the fastest. Typical examples are the addition of ammonia, amines, phosphines, and bisulfite. Alkaline conditions permit the addition of mercaptans, sulfides, ketones, nitroalkanes, and alcohols to acrylamide. Good examples of alcohol reactions are those involving polymeric alcohols such as poly(vinyl alcohol), cellulose, and starch. The alkaline conditions employed with these reactions result in partial hydrolysis of the amide, yielding mixed carbamojdethyl and carboxyethyl products. 

Standards for dmg chemicals are pubUshed ia USP—NE. Dmg substances are chemicals that have therapeutic or diagnostic uses, whereas pharmaceutical iagredients provide preservative action, fiavoiing, or hilfillment of a function ia the formulation of dosage-form dmgs. Examples of dmg substances are acetaminophen [103-90-2] ampicillin [69-53-4] aspirin [50-78-2] powdered ipecac, riboflavin [83-88-5] staimous fluoride [7783-47-3] and thyroid. Examples of pharmaceutical iagredients are ethylparaben [120-47-8] lactose [63-42-3] magnesium stearate [557-04-0] sodium hydroxide [1310-73-2] starch [9005-25-8] and vanillin [121-33-5],... 

Foods high ia sucrose, proteia, or starch (qv) tend to biad water less firmly and must be dried to a low moisture content to obtain microbial StabiHty. For example, grain and wheat flour can support mold growth at moisture contents above 15% (wet basis) and thus are stored at moisture contents below 14%. Stored grains and oil seeds must be kept at a water activity below 0.65 because certain molds can release aflatoxias as they grow. Aflatoxins are potent carciaogens (see Food toxicants, naturally occurring). 

Functional Blends. The term functional blend refers to various ingredient blends formulated to achieve a certain objective such as fat reduction. An example of this blend consists of water, partially hydrogenated canola oil, hydrolyzed beef plasma, tapioca flour, sodium alginate, and salt. This blend is designed to replace animal fat and is typically used at less than 25% of the finished product. Another functional blend is composed of modified food starch, rice flour, salt, emulsifier, and flavor. A recommended formula is 90% meat (with 10% fat), 7% added water, and 3% seasoning blend... 

Oxidation of Carbohydrates. Oxahc acid is prepared by the oxidation of carbohydrates (7—9), such as glucose, sucrose, starch, dextrin, molasses, etc, with nitric acid (qv). The choice of the carbohydrate raw material depends on availabihty, economics, and process operating characteristics. Among the various raw materials considered, com starch (or starch in general) and sugar are the most commonly available. Eor example, tapioka starch is the Brazihan raw material, and sugar is used in India. 

Potassium is required for enzyme activity in a few special cases, the most widely studied example of which is the enzyme pymvate kinase. In plants it is required for protein and starch synthesis. Potassium is also involved in water and nutrient transport within and into the plant, and has a role in photosynthesis. Although sodium and potassium are similar in their inorganic chemical behavior, these ions are different in their physiological activities. In fact, their functions are often mutually antagonistic. For example, increases both the respiration rate in muscle tissue and the rate of protein synthesis, whereas inhibits both processes (42). 

Pyrotechnic mixtures may also contain additional components that are added to modify the bum rate, enhance the pyrotechnic effect, or serve as a binder to maintain the homogeneity of the blended mixture and provide mechanical strength when the composition is pressed or consoHdated into a tube or other container. These additional components may also function as oxidizers or fuels in the composition, and it can be anticipated that the heat output, bum rate, and ignition sensitivity may all be affected by the addition of another component to a pyrotechnic composition. An example of an additional component is the use of a catalyst, such as iron oxide, to enhance the decomposition rate of ammonium perchlorate. Diatomaceous earth or coarse sawdust may be used to slow up the bum rate of a composition, or magnesium carbonate (an acid neutralizer) may be added to help stabilize mixtures that contain an acid-sensitive component such as potassium chlorate. Binders include such materials as dextrin (partially hydrolyzed starch), various gums, and assorted polymers such as poly(vinyl alcohol), epoxies, and polyesters. Polybutadiene mbber binders are widely used as fuels and binders in the soHd propellant industry. The production of colored flames is enhanced by the presence of chlorine atoms in the pyrotechnic flame, so chlorine donors such as poly(vinyl chloride) or chlorinated mbber are often added to color-producing compositions, where they also serve as fuels. 

Thixotropy and Other Time Effects. In addition to the nonideal behavior described, many fluids exhibit time-dependent effects. Some fluids increase in viscosity (rheopexy) or decrease in viscosity (thixotropy) with time when sheared at a constant shear rate. These effects can occur in fluids with or without yield values. Rheopexy is a rare phenomenon, but thixotropic fluids are common. Examples of thixotropic materials are starch pastes, gelatin, mayoimaise, drilling muds, and latex paints. The thixotropic effect is shown in Figure 5, where the curves are for a specimen exposed first to increasing and then to decreasing shear rates. Because of the decrease in viscosity with time as weU as shear rate, the up-and-down flow curves do not superimpose. Instead, they form a hysteresis loop, often called a thixotropic loop. Because flow curves for thixotropic or rheopectic Hquids depend on the shear history of the sample, different curves for the same material can be obtained, depending on the experimental procedure. 

Carbohydrates. Carbohydrates (240—244) of any form are easily sulfated in the presence of solvent, using sulfating reagents such as SO —pyridine, SO —triethjlamine, SO.—trimethyl amine, or chlorosulfonic acid—pyridine. As an example, starch (qv) is sulfated using SO.—trimethyl amine at 0 to 5°C in aqueous media (16). Sulfated carbohydrate products find some use in industry as thickening agents. 

Analytical Methods. A classical and stiU widely employed analytical method is iodimetric titration. This is suitable for determination of sodium sulfite, for example, in boiler water. Standard potassium iodate—potassium iodide solution is commonly used as the titrant with a starch or starch-substitute indicator. Sodium bisulfite occurring as an impurity in sodium sulfite can be determined by addition of hydrogen peroxide to oxidize the bisulfite to bisulfate, followed by titration with standard sodium hydroxide (279). 

Enzymes are specific, however. For example, starch is depolymerized using enzymes to D-glucose (dextrose). The solution of glucose is then treated with glucose isomerase [9055-00-9] to give D-fmctose in about 42% yield. No D-mannose is formed. Addition of isolated D-fmctose to this solution gives the common 55% high fmctose com symp (HFCS) so widely used in soft drinks in the United States. HFCS is about 1.5 times as sweet as sucrose. 

The largest class of processes appHed to farm commodities are separations, which are usually based on some physical property such as density, particle size, or solubiHty. For example, the milling process for cereal grains involves size reduction (qv) foUowed by screening to yield products that have varied concentrations of starch, fiber, and protein. Milling of water slurries is practiced to obtain finer separation of starch, fiber, protein, and oil. 

A rather impressive Hst of materials and products are made from renewable resources. For example, per capita consumption of wood is twice that of all metals combined. The ceUulosic fibers, rayon and cellulose acetate, are among the oldest and stiU relatively popular textile fibers and plastics. Soy and other oilseeds, including the cereals, are refined into important commodities such as starch, protein, oil, and their derivatives. The naval stores, turpentine, pine oil, and resin, are stiU important although their sources are changing from the traditional gum and pine stumps to tall oil recovered from pulping. 

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