Fructose contains 6 carbon atoms and is also a monosaccharide. It exists in a large amount in fruit juice and honey in a free state, and can also combine with glucose to produce sucrose. The raw material for large-scale industrial production of fructose is sucrose, which can be hydrolyzed by dilute hydrochloric acid or invertase, and the product is a mixed solution of fructose and glucose. Adding calcium hydroxide makes fructose and calcium hydroxide form insoluble compounds, which are filtered and separated from the aqueous solution. Then carbon dioxide gas is introduced, so that calcium hydroxide reacts with carbon dioxide to generate calcium carbonate with little solubility, and then the calcium carbonate is filtered out and the water is evaporated to obtain fructose crystals. Another method to produce fructose is to hydrolyze starch into sugar by immobilized glucose isomerase, which contains 42% fructose and 58% glucose. This mixture is called high fructose syrup or high fructose syrup. Fructose is a prismatic crystal with a melting point of 103 ~ 105℃, which is the sweetest of all sugars. The sweetness is twice that of sucrose, and it is widely used in food industry, such as making candy, cake and beverage. The sweetness of high fructose corn syrup is equivalent to that of sucrose, but it is produced from starch, which is not only low in cost, but also has the fragrance of natural honey, and is more widely used in food industry than fructose.

The second fructose is also called levo-sugar. It is a monosaccharide, the full name is D- arabinose, and the molecular formula is C5H 12O5CO. Fructose exists in free form in fruit juice and honey, and it is the only reducing sugar in bovine and human semen. D- fructose stores energy in Jerusalem artichoke (the root of Dahlia) in the form of polysaccharide. A large amount of sucrose exists in the form of glycosidic bond connected with D- glucose. In the crystalline state, there may be β -pyranose in ketose, which is often combined with furanose in natural products. Furofuranose and pyranose coexist in aqueous solution, and there is about 20% of furofuranose in aqueous solution at 20℃. Glycosides formed by fructose are rare in nature. Fructose is a prismatic crystal with melting point 103 ~ 105℃ (decomposition). Fructose is the sweetest of all sugars, about twice as much as sucrose, and can be obtained by hydrolyzing Jerusalem artichoke. Sucrose is the most abundant raw material for large-scale industrial production of fructose. Sucrose is hydrolyzed by dilute acid or invertase, and fructose is separated from the 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. In industry, bromine water can also be used to selectively oxidize glucose in sucrose hydrolysate, and then remove D- gluconic acid to obtain fructose. At present, large-scale industrial production uses starch hydrolysis to prepare glucose, which is converted into invert sugar by immobilized glucose isomerase, which contains 42% fructose and 58% glucose. Commercially known as high fructose syrup or high fructose syrup, it is as sweet as sucrose, but it has the characteristics of natural honey fragrance and low production cost, and has been widely used in food industries such as beverages, sweets and cakes.