Physically Modified Starches

P. Colonna, A. Buleon and C.Mercier, "Physically modified starches," in T. Galliard, ed.. Starch Properties and Potential, 1st Edition, John Wiley Sons, New York, Chap. 4, pp. 79-115, 1987. 

According to the Polish Standard PN-87/A-74820 modified starch is native starch processed in a mode that changes one or more of its initial physical or chemical properties [59], They include roasted starches (e.g., white and yeUow dextrins), acidic and alkaline starches (treated with respectively acids and bases), bleached starches, enzymatically modified starches, physically modified starches (usually heat-treated), and chanically modified starches (via incorporation of specified chemical compounds or via oxidation). These starches, except for the chanically modified ones, are acknowledged by legal regulations as native and are not treated as additives. Hence, the additive substances include the chemically modified starches. 

The increasing use of bioplastics has opened entirely new generations of materials with new performances in comparison with traditional plastics. The possibility offered by physically modified starch to create functionalised nanoparticles able to modify the properties of natural and synthetic mbbers and other synthetic polymers, the naturally high oxygen barrier of starch and its derivatives, and their high permeability to water vapour already offer a range of completely new solutions to the plastic industry. 

Colonna P, Buleon A, Mercier C. 1987. Physically modified starches. In GaUiard, T (editor). Starch Properties and Potential. New York, NY John Wiley Sons, Inc. pp 79-114. 

The most physically modified starch produced nowadays is the thermal-treated or pregelatinized starch. These instant starches are hydrosoluble even in cold water and are frequently used as thickeners in foods that receive minimal heat processing. Pregelatinization methods include drum drying, spray cooking, solvent-based processing, and extrusion (Thomas and Atwell 1999). Most instant starch processes... 

Nonfood Uses. Native com starch is principally used in nonfood appHcations in mining, adhesives, and paper industries. Pregelatinized starch is chemically unmodified, but it is physically modified. Pregelatinized starches are used to decrease water losses in oil-weU drilling muds, in cold water-dispersable wallpaper pastes, and in papermaking as an internal fiber adhesive. 

Modified starch Substance obtained by one or more chemical treatments of edible starches, which may have undergone a physical or enzymatic treatment, and may be acid or alkali thinned or bleached... 

In both their industrial and biological functions, the 3-dimensional characteristics of carbohydrates are important. Many of these stereochemical features are described for carbohydrates in the classic text by Stoddart (2). The inqportance of stereochemistry is underscored by the unique chemical and physical properties of the individual sugars, many of which are configurational isomers. Stereochemistry also plays a role in detentlining the properties of polysaccharides. Molecular shape is as significant for the properties of an industrially modified starch as it is for the recognition of one particular blood type and the rejection of others. 

Physically modified potato starch is preferred in processed foods because of its improved functional properties over those of its native counterpart. Moreover, this modified strach can be safely used in different food products and other industrial applications. Different physical... 

The finished starch slurry from the final hydroclone stage may be further processed in alternative ways (a) dried directly and sold as unmodified com starch (b) modified by chemical or physical treatment in a way that preserves the granule structure, then rewashed to remove residual reactants, and dried (c) gelatinized and dried (d) chemically or physically modified and then dried (e) hydrolyzed either completely to D-glucose or partially hydrolyzed to give mixtures of soluble oligosaccharides and D-glucose (see Chapter 21), which can be fermented to yield ethanol and other products. 

Starch modifications can be classified as physical modifications, chemical modifications and genetic modifications.45 Physical modification of cassava starch involves application of shear force, blending and thermal treatment. A combination of thermal treatment and shear force has been widely used to produce many extruded products and snacks. Well-known physically modified cassava starch products are alpha starch or pregelatinized starch and heat-moisture treated starch. 

Dry, unheated starch is stable if protected from high humidity, when used as a diluent or disintegrant in solid-dosage forms, starch is considered to be inert under normal storage conditions. However, heated starch solutions or pastes are physically unstable and are readily attacked by microorganisms to form a wide variety of starch derivatives and modified starches that have unique physical properties. 

Sterilizable maize starch is a chemically or physically modified corn (maize) starch that does not gelatinize on exposure to moisture or steam sterilization. Sterilizable maize starch is primarily used as a lubricant for examination and surgeons gloves although because of safety concerns unlubricated gloves are now generally recommended. It is also used as a vehicle for medicated dusting powders. 

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