Question

D-fructose is used for sweetening cold drinks but not hot ones because:
(A) it is not a true carbohydrate
(B) on heating it is converted into pyranose form
(C) on heating it is converted into furanose form
(D) on heating it gets decomposed

Answer 1

Hint: Sweeteners are food additives that are used or intended to be used as a tabletop sweetener or to impart a sweet taste to food. Fructose is sweeter than glucose due to its stereomerism structure. In a sugar, the D or L designation refers to the configuration of the chiral carbon farthest from the aldehyde or keto group.

Complete answer:
D-fructose is a monosaccharide in sweet fruits and honey that is soluble in water, alcohol, or ether. It is used as a preservative and an intravenous infusion in parenteral feeding. In equilibrium, D-fructose exists in two forms: pyranose and furanose. Monosaccharides with 5-membered rings are called furanoses and those with 6 membered rings are pyranoses because their heterocyclic ring skeletons contain an O atom analogous to the rings of the simple cyclic ethers furan and pyran.
Depending on the system's temperature, these two forms switch places. Because the furanose form of fructose is less sweet than the pyranose form, the equilibrium shifts to the furanose structure as the temperature rises, making the solution less sweet.
Therefore, D-fructose is used as a sweetening agent for cold drinks but not for hot ones because on heating it is converted to furanose form.
Hence, Option (C) is correct.

Note:
Low-calorie citrus base and cola-type soft drinks were prepared using $10\%$ sucrose isosweet sugar-saccharin mixtures as sweeteners. The proportion of saccharin in the mixture, in which the aftertaste of saccharin was not noticed, was determined by an experienced taste panel.