Fructose is often recommended for, and consumed by, people with diabetes mellitus or hyperglycemia, because it has a very low glycemic index (GI) relative to sugar (sucrose). However, this benefit is tempered by concern that fructose may have an adverse effect on plasma lipid and uric acid levels, and the resulting higher blood levels of fructose can be damaging to proteins. The low GI is due to the unique and lengthy metabolic pathway of fructose, which involves phosphorylation and a multi-step enzymatic process in the liver.

Crystalline fructose and high-fructose corn syrup are often mistakenly confused as the same product. The former is simply pure (100%) fructose. The latter is composed of nearly equal amounts of fructose and glucose. Crystalline fructose is held to offer many unique benefits such as improved product texture, taste and stability. Specifically, when combined with other sweeteners and starches, crystalline fructose is said to boost cake height (in baked goods) and mouth-feel of foods and beverages and to produce a pleasing brown surface color and pleasant aroma when baking.

Lactose is a disaccharide that consists of β-D-galactose and β-D-glucose molecules bonded through a β1-4 glycosidic linkage.

Lactose has a solubility of 1 in 4.63 measured %w/v. This translates to 0.216 g of lactose dissolving readily in 1 mL of water. The solubility of lactose in water is 18.9049 g at 25°C, 25.1484 g at 40°C and 37.2149 g at 60°C per 100 g solution. Its solubility in ethanol is 0.0111 g at 40°C and 0.0270 g at 60°C per 100 g solution.

Like other carbohydrates, sucrose has a hydrogen to oxygen ratio of 2:1. It consists of two monosaccharides, α-glucose and fructose, joined by a glycosidic bond between carbon atom 1 of the glucose unit and carbon atom 2 of the fructose unit. What is notable about sucrose is that unlike most polysaccharides, the glycosidic bond is formed between the reducing ends of both glucose and fructose, and not between the reducing end of one and the nonreducing end of the other. The effect of this inhibits further bonding to other saccharide units. Since it contains no free anomeric carbon atom, it is classified as a nonreducing sugar. Sucrose melts and decomposes at 186 °C to form caramel, and when combusted produces carbon, carbon dioxide, and water. Water breaks down sucrose by hydrolysis, however the process is so gradual that it could sit in solution for years with negligible change. If the enzyme sucrase is added however, the reaction will proceed rapidly.

Reacting sucrose with sulfuric acid dehydrates the sucrose and forms the element carbon, as demonstrated in the following equation:

C₁₂H₂₂O₁₁ + H₂SO₄ catalyst → 12 C + 11 H₂O

>>> from: http://en.wikipedia.org/wiki/Sucrose

Sugar (the word stems from the Sanskrit sharkara) consists of a class of edible crystalline substances including sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple (in maple syrup), and in many other sources. It forms the main ingredient in much candy. “Excessive” consumption of sugar has been associated with increased incidences of type 2 diabetes, of obesity and of tooth decay.

In non-scientific use, the term sugar refers to sucrose ( also called “table sugar” or “saccharose” ) – a white crystalline solid disaccharide. In this informal sense, the word “sugar” principally refers to crystalline sugars.

Humans most commonly use sucrose as their sugar of choice for altering the flavor and properties (such as mouthfeel, preservation, and texture) of beverages and food. Commercially produced table sugar comes either from sugar cane or from sugar beet. Manufacturing and preparing food may involve other sugars, including palm sugar and fructose, generally obtained from corn (maize) or from fruit.

Sugar may dissolve in water to form a syrup. A great many foods exist which principally contain dissolved sugar. Generically known as “syrups”, they may also have other more specific names such as “honey” or “molasses“.

Scientifically, sugar refers to any monosaccharide or disaccharide. Monosaccharides ( also called “simple sugars” ), such as glucose, store chemical energy which biological cells convert to other types of energy.

In a list of ingredients, any word that ends with “-ose” (such as “glucose”, “dextrose”, “fructose”, etc.) will likely denote a sugar. Sometimes such words may also refer to any types of carbohydrates soluble in water.

Glucose (a type of sugar found in human blood plasma) has the molecular formula C₆ H₁₂ O₆.

In culinary terms, the foodstuff known as sugar delivers a primary taste sensation of sweetness. Apart from the many forms of sugar and of sugar-containing foodstuffs, alternative non-sugar-based sweeteners exist, and these particularly attract interest from people who have problems with their blood sugar level (such as diabetics) and people who wish to limit their calorie-intake while still enjoying sweet foods. Both natural and synthetic substitutes exist with no significant carbohydrate (and thus low-calorie) content: for instance stevia (a herb), and saccharin (produced from naturally occurring but not necessarily naturally edible substances by inducing appropriate chemical reactions).

>>> from: http://en.wikipedia.org/wiki/Sugar