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  Production of enzyme-resistant starch by extrusionUSPTO Application #: 20070275155Title: Production of enzyme-resistant starch by extrusion Abstract: A process for producing alpha-amylase resistant starch comprises extruding a feed starch at a temperature in the range of about 60-220° C., thereby producing a product alpha-amylase resistant starch. The feed starch can be in the form of an aqueous slurry or paste that has a dry solids concentration of at least about 50% by weight. The process optionally can include the additional step of heating the product starch to a temperature of at least about 90° C. in the presence of moisture, to increase further the alpha-amylase resistance of the product. (end of abstract) Agent: Williams, Morgan & Amerson - Houston, TX, US Inventors: Warren L. Nehmer, Geoffrey A.R. Nobes, Walter C. Yackel USPTO Applicaton #: 20070275155 - Class: 426661000 (USPTO) Related Patent Categories: Food Or Edible Material: Processes, Compositions, And Products, Products Per Se, Or Processes Of Preparing Or Treating Compositions Involving Chemical Reaction By Addition, Combining Diverse Food Material, Or Permanent Additive, Carbohydrate Containing, Carbohydrate Is Starch The Patent Description & Claims data below is from USPTO Patent Application 20070275155. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] Starch comprises two polysaccharides: amylose and amylopectin. Amylose is a generally linear polymer of glucose units connected by alpha 1-4 glycosidic linkages. Amylopectin is a branched polymer in which many of the glucose units are connected by alpha 1-4 glycosidic linkages, but some are connected by alpha 1-6 glycosidic linkages. [0002] Alpha-amylase is an enzyme that is present in the human body and which hydrolyzes alpha 1-4 linkages in starch, thus leading to digestion of the starch. In certain situations it is desirable to produce starch that resists hydrolysis by alpha-amylase, for example to decrease the caloric content of the starch, or to increase its dietary fiber content. However, attempts to produce such starch in the past have suffered from one or more problems, such as process complexity and expense. [0003] There is a need for improved processes for making starches that are resistant to alpha-amylase. SUMMARY OF THE INVENTION [0004] One embodiment of the invention is a process for producing alpha-amylase resistant starch. The process comprises extruding a feed starch at a temperature in the range of about 60-220.degree. C., thereby producing a product starch that is resistant to alpha-amylase. [0005] In some embodiments of the process, the feed starch is a high amylose starch, for example one that comprises at least about 50% by weight amylose, or in some cases at least about 65% by weight amylose. Other starches can be used in the process as well. Examples of suitable starch sources include corn, potato, tapioca, rice, pea, wheat, or a combination of two or more thereof. [0006] In some embodiments, the feed starch is dry starch, and water or an aqueous composition can be added to the extruder to form a slurry or paste therein. In other embodiments, the feed starch is in an aqueous slurry or paste that has a dry solids concentration of at least about 50% by weight, or in some cases, at least about 60% or 70% by weight. [0007] Some embodiments of the process include the additional step of heating the product starch to a temperature of at least about 90.degree. C. in the presence of moisture. In certain embodiments of the process, this heat-moisture treatment step can be performed at a temperature of at least about 120.degree. C., or in some cases at least about 150.degree. C., with a moisture content of about 15-35% by weight. In certain embodiments, the moisture content of the product starch during this step is about 20-25% by weight. In some embodiments of the process, the total dietary fiber content of the product starch is increased to at least about 50% by weight by the heating in the presence of moisture. DESCRIPTION OF SPECIFIC EMBODIMENTS [0008] One embodiment of the present invention is a process in which alpha-amylase resistant starch is produced by extruding a feed starch at a temperature in the range of about 60-220.degree. C. The term "alpha-amylase resistant starch" is used in this patent to refer to a starch that has a component that is resistant to alpha-amylase. It should be understood that the starch can also have components that are not alpha-amylase resistant. [0009] The feed starch can be a high amylose starch, for example one that comprises at least about 50% by weight amylose, or at least about 65% by weight amylose. Such high amylose starches are commercially available. Alternatively, starches that are not as high in amylose can be used. [0010] The starch used in the process can come from a variety of sources, including starches obtained from dent corn, high amylose ae genetic corn (ae is the name of a genetic mutation commonly known by corn breeders and is short for "amylose extender"), potato, tapioca, rice, pea, and wheat varieties, as well as purified amylose from these starches, and alpha-1,4 glucans produced according to international patent application WO 00/14249, which is incorporated herein by reference. Combinations of two more types of starches can also be used in the present invention. [0011] Chemically modified starches, such as hydroxypropyl starches, starch adipates, acetylated starches, and phosphorylated starches, can also be used in the present invention to produce resistant starch. For example, suitable chemically modified starches include, but are not limited to, crosslinked starches, acetylated and organically esterified starches, hydroxypropylated starches, phosphorylated and inorganically esterified starches, cationic, anionic, nonionic, and zwitterionic starches, and succinate and substituted succinate derivatives of starch. Such modifications are known in the art, for example in Modified Starches: Properties and Uses, Ed. Wurzburg, CRC Press, Inc., Florida (1986). Other suitable modifications and methods are disclosed in U.S. Pat. Nos. 4,626,288, 2,613,206 and 2,661,349, which are incorporated herein by reference. [0012] In one embodiment of the process, the feed starch can be a dry product "Dry" is this context does not mean that the moisture content is 0%, but that the moisture content is low enough to be regarded as dry in a commercial sense. When the feed is dry starch, water or an aqueous composition can be added to the extruder to form a slurry or paste therein. [0013] In another embodiment of the process, the starch is fed to the extruder while it is in the form of an aqueous slurry or paste that has a dry solids concentration of at least about 50% by weight. In some cases, the dry solids concentration of slurry or paste can be at least about 60% by weight, or at least about 70% by weight. The use of such a high solids concentration enhances rapid crystallization of resistant starch crystallites. [0014] The water used in the feed starch and/or added to the extruder can optionally comprise one or more other substances, such as lower alkanols (e.g., alkanols having 1-6 carbon atoms) or salts. The pH can vary from about 3.5 to about 8.5. [0015] In general, extrusion apparatus is well suited to handle high-viscosity, high-solids compositions. Specific examples include single-screw and twin-screw extruders. Such extrusion apparatus is commercially available. [0016] In some embodiments of the process, the temperature of the feed starch during extrusion is in the range of about 70-145.degree. C. It should be understood that the temperature of the starch need not remain constant during extrusion. For example, the extrusion apparatus can comprise more than one zone, and each zone can be held at a different temperature, although preferably the temperature of each zone is within the broad ranges stated herein. [0017] The product starch produced by the process will in many cases have a total dietary fiber (TDF) content of at least about 30% by weight This can be increased by the additional step of heating the product starch to a temperature of at least about 90.degree. C. in the presence of moisture. The temperature of this heat-moisture treatment step optionally can be at least about 120.degree. C., or in some cases at least about 150.degree. C. The moisture content during this step can be about 15-35% by weight, or in some cases about 20-25% by weight. In order to achieve the desired moisture content during this step, it will be necessary in many cases to add water or an aqueous composition to the product starch. This heat-moisture treatment can increase the TDF of the starch to at least about 50% by weight, and in some cases even higher. [0018] The starch can then be dried. For example, a tray dryer or flash dryer can be used to remove moisture from the wet starch cake, although other drying techniques could be used as well. Persons skilled in this art will understand that a "dry starch product" normally does not have 0% moisture content, but has a low enough moisture content to be considered "dry" for commercial purposes. [0019] The starch product optionally can be milled to reduce its particle size, either before or after heat-moisture treatment. Milling will usually be performed on dried starch. [0020] The starch produced by the process generally is heat-stable and shear-stable, which makes it compatible with high temperature and/or high shear processing. As a result, the starch is well-suited for use in food applications such as baking and frying. In addition, the starch is relatively high in total dietary fiber (TDF). [0021] Resistant starch (RS) has been classified into four different types: Type I results from the starch being physically inaccessible to alpha-amylase (e.g. starch embedded in a protein or fiber matrix, such as found in whole grain); Type II is intact, native starch granules that as uncooked starch has a physical structure that is digestive resistant, but after gelatinization upon cooking is digestible (e.g. potato and banana starch); Type III is starch that has been cooked and gelatinized, or otherwise the native structure has been destroyed, and the starch molecules have re-associated themselves during the processing so that the starch is alpha-amylase resistant after cooking; and Type IV is a result of starch chemical modification which interferes with alpha-amylase digestion. The starch produced by the present process is typically a Type III resistant starch, although it can be Type IV resistant starch when chemically modified starch is used as the starting material. 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