Is fructose a reducing sugar?

In daily life, most people don’t know much about fructose. Fructose, also known as levulose, is a type of monosaccharide and is different from ordinary sugars. It is the only reducing sugar, so fructose is a reducing sugar. It is the sweetest of all sugars. It can also be used to make candies, cakes, and beverages, and has a wide range of uses.

1 fructose

Fructose contains 6 carbon atoms and is also a monosaccharide. It is an isomer of glucose. It exists in large quantities in fruit juice and honey in a free state. Fructose can also combine with glucose to form sucrose. Pure fructose is a colorless crystal with a melting point of 103-105°C. It is not easy to crystallize and is usually a viscous liquid. It is easily soluble in water, ethanol and ether.

The raw material for large-scale industrial production of fructose is sucrose. Sucrose can be hydrolyzed using dilute hydrochloric acid or invertase, and the product is a mixed solution of fructose and glucose. Calcium hydroxide is added to form an insoluble compound between fructose and calcium hydroxide, which is separated from the aqueous solution by filtration. Carbon dioxide gas is then introduced to allow calcium hydroxide to react with carbon dioxide to generate calcium carbonate with very low solubility. The calcium carbonate is then filtered out and the water is evaporated to obtain fructose crystals.

Another method of producing fructose is to use starch as raw material. After starch hydrolysis, it is converted into sugar by immobilized glucose isomerase, which contains 42% fructose and 58% glucose. This mixture is called high fructose corn syrup or high fructose syrup.

Fructose is a prismatic crystal with a melting point of 103-105°C. It is the sweetest of all sugars, twice as sweet as sucrose. It is widely distributed in plants and is widely used in the food industry, such as making candy, cakes, beverages, etc. The sweetness of high fructose corn syrup is comparable to that of sucrose, but it is produced using starch as raw material. It is not only low in cost but also has the aroma of natural honey. It has a wider range of uses in the food industry than fructose.

2 Fructose 2

Also known as levulose. It is a monosaccharide, its full name is D-arabinohexose[1], and its molecular formula is C5H12O5CO. Fructose exists in large quantities in fruit juice and honey in free form, and is the only reducing sugar present in cattle and human semen. In Jerusalem artichoke (root of dahlia), D-fructose stores energy in the form of polysaccharides. The larger existing form is sucrose connected with D-glucose by glycosidic bonds. In the crystalline state, β-pyranose may exist in ketose, which is often combined with furanose in natural products. In aqueous solution, furanose and pyranose exist simultaneously, and there is about 20% furanose in aqueous solution at 20°C.

Glycosides formed from fructose are rarely found in nature. Fructose is a prismatic crystal with a melting point of 103-105°C (decomposition). Fructose is the sweetest of all sugars, about twice as sweet as sucrose, and can be obtained by hydrolysis of Jerusalem artichoke. Sucrose is the most abundant raw material for large-scale industrial production of fructose. Sucrose is hydrolyzed with dilute acid or invertase to separate fructose from a solution mixed with D-glucose. Fructose is not easy to crystallize, but it forms an insoluble complex with calcium hydroxide. After separation, fructose crystals can be obtained by introducing carbon dioxide. Bromine water can also be used industrially to selectively oxidize glucose in the hydrolyzate of sucrose, and then remove D-gluconic acid to obtain fructose. At present, glucose is prepared by starch hydrolysis in large-scale industrial production, and then converted into invert sugar by immobilized glucose isomerase, which contains 42% fructose and 58% glucose. It is commercially called high fructose corn syrup or high fructose syrup. Its sweetness is comparable to that of sucrose, but it has the characteristics of natural honey flavor and low production cost. It has been widely used in food industries such as beverages and confectionery.

3 Fructose 3

C6H12O6 One of the alcohol and ketone monosaccharides. White crystals or powder, the product is often light brown and tastes very sweet. Density 1.6g/cm3, melting point 103~105℃ (decomposition). Soluble in water, ethanol and ether. It has no aldehyde group but has an active ketone group, and can undergo a silver mirror reaction. The oxidation products are glycolic acid and trihydroxybutyric acid. It can form calcium fructose precipitate with lime water, but fructose can be recovered by introducing carbon dioxide. Used as food, nutritional supplement and preservative. Found in fruits and honey. It is often produced by hydrolysis of inulin.

4 Fructose 4

Silver mirror reaction of fructose

Glucose and fructose are isomers of each other. Glucose is a polyhydroxy aldehyde (aldose) and fructose is a polyhydroxy ketone (ketose). There is no aldehyde group in the fructose molecule, so it seems that the silver mirror reaction cannot occur. However, this is not the case. The main reason is that fructose can undergo two reactions in alkaline solution: one is that it becomes aldose through enolization (reaction equation omitted). The second is that cracking occurs to produce organic matter containing aldehyde groups (chemical formula omitted). From this we can see that fructose solutions always contain aldose and aldehyde-containing organic matter, which can react with alkaline silver ammonia solutions to produce a silver mirror reaction. Therefore, both fructose and glucose are reducing sugars. The effect of using fructose in the silver mirror reaction is similar to that of glucose, and the reaction conditions are slightly higher than those of glucose, 60-100°C, the mass fraction of fructose solute can be 1%, and the mass fraction of silver nitrate solution and ammonia solute can be 2%-4%. Under this condition, a high-quality silver mirror can be obtained.