CHEMISTRY GLOSSARY

maltose    →   maltoza

Maltose (malt sugar) is a disaccharide which is obtained with hydrolytic decomposition of starch in the presence of enzyme amylase. Maltose is composed of two glucose molecules linked by an α(1→4)-glycosidic linkage. Maltose has an alpha acetal.

yeast    →   kvasac

Yeasts are a group of unicellular fungi which exist almost everywhere in nature. There are about 1500 species currently known to science. Yeast contains an enzyme called cimase which catalyses change of glucose in ethanol in the process of alcoholic fermentation.

disaccharide    →   disaharid

Disaccharides are compounds in which two monosaccharides are joined by a glycosidic bond. A glycosidic bond to the anomeric carbon can be either α or β. For example, maltose, the disaccharide obtained by enzyme-catalyzed hydrolysis of starch, consists of two D-glucopyranose units joined by a 1,4’-α-glycoside bond. The "prime" superscript indicates that C-4 is not in the same ring as C-1. Unlike the other disaccharides, sucrose is not a reducing sugar and does not exhibit mutarotation because the glycosidic bond is between the anomeric carbon of glucose and the anomeric carbon of fructose.

epimer    →   epimer

Epimers are diastereoisomers that have the opposite configuration at only one of two or more chiral centers present in the respective molecular entities. For example D-glucose and D-mannose, which differ only in the stereochemistry at C-2, are epimers, as are D-glucose and D-galactose (which differ at C-4).

fructose    →   fruktoza

Fructose (fruit sugar) is a ketohexose (a six-carbon ketonic sugar), which occurs in sweet fruits and honey. Glucose and fructose have the same molecular formula, C₆H₁₂O₆, but have different structures. Pure, dry fructose is a very sweet, white, odorless, crystalline solid. Fructose is one of the sweetest of all sugars and is combined with glucose to make sucrose, or common table sugar. An older common name for fructose is levulose, after its levorotatory property of rotating plane polarized light to the left (in contrast to glucose which is dextrorotatory). The polysaccharide inulin is a polymer of fructose.

glycogen    →   glikogen

Glycogen (animal starch) is a polysaccharide that serves the same energy storage function in animals that starch serves in plants. Dietary carbohydrates not needed for immediate energy are converted by the body to glycogen for long term storage (principally in muscle and liver cells). Like amylopectin found in starch, glycogen is a polymer of α(1→4)-linked subunits of glucose, with α(1→6)-linked branches. Glycogen molecules are larger than those of amylopectin (up to 100 000 glucose units) and contain even more branches. Branch points occur about every 10 residues in glycogen and about every 25 residues in amylopectin. The branching also creates lots of ends for enzyme attack and provides for rapid release of glucose when it is needed.

glycosidic bond    →   glikozidna veza

Glycosidic bond ia a bond between the glycosyl group, the structure obtained by removing the hydroxy group from the hemiacetal function of a monosaccharide, and the -OR group (which itself may be derived from a saccharide and chalcogen replacements thereof (RS–, RSe–). The terms N-glycosides and C-glycosides are misnomers and should not be used. The glycosidic bond can be α or β in orientation, depending on whether the anomeric hydroxyl group was α or β before the glycosidic bond was formed and on the specificity of the enzymatic reaction catalyzing their formation. Once the glycosidic bond is formed, the anomeric configuration of the ring is locked as either α or β. Specific glycosidic bonds therefore may be designated α(1→4), β(1→4), α(1→6), and so on. Cellulose is formed of glucose molecules linked by β(1→4)-glycosidic bonds, whereas starch is composed of α(1→4)-glycosidic bonds.

hemiacetal    →   poluacetal

Hemiacetals are organic compounds having the general formula R₂C(OH)OR’ (R’ ≠ H), derived from aldehydes or ketones by formal addition of an alcohol to the carbonyl group. Hemiacetals are generally unstable compounds. In some cases however, stable cyclic hemiacetals can be readily formed, especially when 5- and 6-membered rings are possible. In this case an intramolecular OH group reacts with the carbonyl group. Glucose and many other aldoses exist as cyclic hemiacetals whereas fructose and similar ketoses exist as cyclic hemiketals. Originally, the term was confined to derivatives of aldehydes (one R = H), but it now applies equally to derivatives of ketones (neither R = H).

high fructose corn syrup    →   visoko fruktozni kukuruzni sirup

High fructose corn syrup (HFCS) is commonly used in place of sugar in foods and drinks. Corn starch is hydrolyzed to glucose, which is then treated with glucose isomerase to produce a fructose-rich mixture. HFCS is available in a number of forms, named according to the percentage of fructose they contain, HFCS-55 for instance contains 55 % fructose and 45 % glucose. The enhanced sweetness, low cost and ease of use are the main reasons why manufacturers now prefer to use high fructose corn syrup instead of sugar.

hydrolysis    →   hidroliza

Hydrolysis is a chemical reaction in which water reacts with another substance to form two or more new substances. This involves ionisation of the water molecule, as well as splitting of the compound hydrolysed, e.g.

Examples are conversion of starch to glucose by water in the presence of suitable catalysts and a reaction of the ions of a dissolved salt to form various products, such as acids, complex ions, etc.