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Starch gelatinization is a process of breaking down the intermolecular bonds of starch molecules in the presence of water and heat, allowing the hydrogen bonding sites (the hydroxyl hydrogen and oxygen) to engage more water. This irreversibly dissolves the starch granule in water. Water acts as a plasticizer. Three main processes happen to the starch granule: granule swelling, crystal or double helical melting, and amylose leaching. *During heating, water is first absorbed in the amorphous space of starch, which leads to a swelling phenomenon.〔Jenkins, P J, and A M. Donald. "Gelatinisation of Starch: a Combined Saxs/waxs/dsc and Sans Study." Carbohydrate Research. 308 (1998): 133-147. Print.〕 *Water then enters via amorphous regions the tightly bound areas of double helical structures of amylopectin. At ambient temperatures these crystalline regions do not allow water to enter. Heat causes such regions to become diffuse, the amylose chains begin to dissolve, to separate into an amorphous form and the number and size of crystalline regions decreases. Under the microscope in polarized light starch loses its birefringence and its extinction cross. 〔Zobel, H. F. (1988), Starch Crystal Transformations and Their Industrial Importance. Starch - Stärke, 40: 1–7. 〕 *Penetration of water thus increases the randomness in the starch granule structure, and causes swelling, eventually soluble amylose molecules leach into the surrounding water and the granule structure disintegrates. The gelatinization temperature of starch depends upon plant type and the amount of water present, pH, types and concentration of salt, sugar, fat and protein in the recipe, as well as starch derivatisation technology used. Some types of unmodified native starches start swelling at 55 °C, other types at 85 °C.〔Hans-Dieter Belitz, Werner Grosch, Peter Schieberle, ''Food chemistry'', Edition 3, Springer, page: 318-323, year: 2004, ISBN 3-540-40818-5, ISBN 978-3-540-40818-5〕 The gelatinization temperature of modified starch depends on for example on the degree of cross-linking of the amylopectin, the degree of acid treatment, acetylation. Gel temperature can also be modified by genetic manipulation of starch synthase genes. Gelatinization temperature also depends on the amount of damaged starch granules. These will swell faster. Damaged starch can be produced, for example, during the wheat milling process, or when drying the starch cake in the starch plant.〔Stanley P. Cauvain, Linda S. Young, ''Baking problems solved'', Woodhead Publishing, page: 25-26, year: 2001, ISBN 1-85573-564-4, ISBN 978-1-85573-564-4 〕 There is an inverse correlation between gelatinization temperature and glycemic index.〔 Gelatinization improves the availability of starch for amylase hydrolysis. So gelatinisation of starch is used constantly in cooking to make the starch digestable or to thicken/bind water in roux sauce, a soup. ==Retrogradation== (詳細はgel) and rearrange itself again to a more crystalline structure; this process is called retrogradation. During cooling, starch molecules gradually aggregate to form a gel. Molecular associations occur: Amylose-Amylose ; Amylose-Amylopectin; Amylopectin-Amylopectin. A mild association amongst chains come together with water still embedded in the molecule. Due to the tightly packed organization of small granule starches, retrogradation occurs much more slowly compared to larger starch granules. High amylose starches require more energy to break up bonds to gelatinize into starch molecules, leading to a rigid and stiff gel. A mild association amongst chains come together with water still embedded in the molecule. Due to strong associations of hydrogen bonding, longer amylose molecules will form a stiff gel.〔Hegenbart. S.. Understanding starch functionality. Food product. Web. 1996 http://www.foodproductdesign.com/articles/1996/01/understanding-starch-functionality.aspx〕 Amylopectin molecules with longer branched structure, increases the tendency to form strong gels. Granule size do not directly impact starch performance, but it is one of the main factors affecting starch gelatinzation and retrogradation. High amylopectin starches will have a stable gel, but will be softer than high amylose gels. Retrogradation restricts the availability for amylase hydrolysis to occur. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「starch gelatinization」の詳細全文を読む スポンサード リンク
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