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Gelatin
Gelatin or gelatine (from (ラテン語:gelatus) meaning "stiff", "frozen") is a translucent, colorless, brittle (when dry), flavorless food derived from collagen obtained from various animal by-products. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar way are called ''gelatinous''. Gelatin is an irreversibly hydrolyzed form of collagen. It is found in most gummy candy as well as other products such as marshmallows, gelatin desserts, and some ice creams, dips and yogurts. Household gelatin comes in the form of sheets, granules, or powder. Instant types can be added to the food as they are; others need to be soaked in water beforehand.
==Composition and properties==
Gelatin is a mixture of peptides and proteins produced by partial hydrolysis of collagen extracted from the skin, bones, and connective tissues of animals such as domesticated cattle, chicken, pigs, horses and fish. During hydrolysis, the natural molecular bonds between individual collagen strands are broken down into a form that rearranges more easily. Its chemical composition is, in many respects, closely similar to that of its parent collagen. Photographic and pharmaceutical grades of gelatin are generally sourced from beef bones and pig skin.
Gelatin readily dissolves in hot water, and sets to a gel on cooling. Gelatin added directly to cold water does not dissolve well. Gelatin is also soluble in most polar solvents. Gelatin solutions show viscoelastic flow and streaming birefringence. The solubility of the gelatin is determined by the method of manufacture. Typically, gelatin can be dispersed in a relatively concentrated acid. Such dispersions are stable for 10–15 days with little or no chemical changes and are suitable for coating purposes or for extrusion into a precipitating bath.
The mechanical properties of gelatin gels are very sensitive to temperature variations, the previous thermal history of the gel, and time. These gels exist over only a small temperature range, the upper limit being the melting point of the gel, which depends on gelatin grade and concentration but is typically less than and the lower limit the freezing point at which ice crystallizes. The upper melting point is below human body temperature, a factor which is important for mouthfeel of foods produced with gelatin. The viscosity of the gelatin/water mixture is greatest when the gelatin concentration is high and the mixture is kept cool at about . The gel strength is quantified using the Bloom test.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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