فروکتوز

فروکتوز مونوساکاریدی شش کربنه است. فرمول شیمیایی آن C6H۱۲O۶ بوده لذا ایزومر گلوکز و گالاکتوز است.
این کتوز، یکی از سه سوخت اصلی بدن است. نام دیگر آن لولز است و در تمامی میوه های شیرین مانند انگور یافت می شود. همچنین زنبورها طی فرآیندی با ترشح آنزیم هایی مانند دیاستاز نکتار ( شهدهای گیاهی ) جمع آوری شده را فرآوری می کنند و قندهای نکتار را ( مانند ساکارز ) به فروکتوز و گلوکز تبدیل می کنند. عسل حاصله حاوی حدودا" ۳۴٪ فروکتوز می باشد. فروکتوز قند مفیدی است که از بروز بعضی بیماری های مزمن جلوگیری می کند. مصرف فروکتوز باعث کاهش ترشح انسولین از سلول های بتای لوزالمعده می شود. [نیازمند منبع]
خواص فروکتوز [ویرایش]
خواص فروکتوز عبارتند از: شیرینی آن ۷/۱ برابر شکر است، با استفاده از فرآوری مخلوطی از گلوکز و فروکتوز شربت غنی از فروکتوز یا HFS با غلظت های متفاوت ( معمولا" در سه غلظت ۴۲٪، ۵۵٪ و ۹۰٪ فروکتوز ) تولید می گردد که در بهبود افراد مبتلا به دیابت مفید است. همچنین بر خلاف ساکارز نیازی به شکسته شدن در بدن ندارد و میتواند مستقیما در روده جذب شود. فروکتوز در تمامی موارد استفاده از شکر می تواند جایگزین آن شود. [نیازمند منبع]
از ویکی پدیا
قس
Fructose, or fruit sugar, is a simple monosaccharide found in many plants. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed directly into the bloodstream during digestion. Fructose was discovered by French chemist Augustin - Pierre Dubrunfaut in 1847. [3] Pure, dry fructose is a very sweet, white, odorless, crystalline solid and is the most water - soluble of all the sugars. [4] From plant sources, fructose is found in honey, tree and vine fruits, flowers, berries and most root vegetables. In plants, fructose may be present as the monosaccharide and/or as a component of sucrose. Commercially, fructose is usually derived from sugar cane, sugar beets and corn and there are three commercially important forms. Crystalline fructose is the monosaccharide, dried and ground, and of high purity. High - fructose corn syrup ( HFCS ) is a mixture of glucose and fructose as monosaccharides. Sucrose is the third form. All forms of fructose, including fruits and juices, are commonly added to foods and drinks for palatability, taste enhancement and improved browning of some foods, such as baked goods.
About 240, 000 tons of crystalline fructose are produced annually. [5]
Contents [show]
[edit]Chemical properties
Figure 1: Relationship between the acyclic and the cyclic ( hemiketal ) isomers of fructose.
d - and l - isomers of fructose ( open - chain form )
Fructose is a 6 - carbon polyhydroxyketone. It is an isomer of glucose; i. e. , both have the same molecular formula ( C6H12O6 ) but they differ structurally. Crystalline fructose adopts a cyclic six - membered structure owing to the stability of its hemiketal and internal hydrogen - bonding. This form is formally called D - fructopyranose. In solution, fructose exists as an equilibrium mixture of 70% fructopyranose and about 22% fructofuranose, as well as small amounts of three other forms, including the acyclic structure. [6]
[edit]Reactions
[edit]Fructose and fermentation
Fructose may be anaerobically fermented by yeast or bacteria. [7] Yeast enzymes convert sugar ( glucose, or fructose ) to ethanol and carbon dioxide. The carbon dioxide released during fermentation will remain dissolved in water, where it will reach equilibrium with carbonic acid, unless the fermentation chamber is left open to the air. The dissolved carbon dioxide and carbonic acid produce the carbonation in bottle fermented beverages. [8]
[edit]Fructose and Maillard reaction
Fructose undergoes the Maillard reaction, non - enzymatic browning, with amino acids. Because fructose exists to a greater extent in the open - chain form than does glucose, the initial stages of the Maillard reaction occurs more rapidly than with glucose. Therefore, fructose potentially may contribute to changes in food palatability, as well as other nutritional effects, such as excessive browning, volume and tenderness reduction during cake preparation, and formation of mutagenic compounds. [9]
[edit]Dehydration
Fructose readily dehydrates to give hydroxymethylfurfural ( "HMF" ) . This process may in the future be part of a low - cost, carbon - neutral system to produce replacements for petrol and diesel from plantations. [10]
[edit]Physical and functional properties
[edit]Relative sweetness
The primary reason that fructose is used commercially in foods and beverages, besides its low cost, is its high relative sweetness. It is the sweetest of all naturally occurring carbohydrates. Fructose is generally regarded as being 1. 73 times as sweet as sucrose. [11][12] However, it is the 5 - ring form of fructose that is sweeter; the 6 - ring form tastes about the same as usual table sugar. Warming fructose leads to formation of the 6 - ring form. [13]
Figure 2: Relative sweetness of sugars and sweeteners.
The sweetness of fructose is perceived earlier than that of sucrose or dextrose, and the taste sensat . . .