Question

Which of the following statements is incorrect?
A) all monosaccharide whether aldose or ketose are reducing sugars
B) lactose is present in milk
C) Fehling solution and Tollen's reagent can reduce non-reducing sugars
D) glucose is aldohexose

Answer 1

Any sugar that may function as a reducing agent is referred to as reducing sugar. Reducing sugar creates an aldehyde or ketone in an alkaline solution, allowing it to function as a reducing agent, as in Benedict's reagent. The sugar forms a carboxylic acid as a result of this reaction.

Complete answer:
All monosaccharides, as well as certain disaccharides, oligosaccharides, and polysaccharides, are reducing sugars. The aldoses, which have an aldehyde group, and the ketoses, which have a ketone group, are the two types of monosaccharides. Before ketoses to serve as reducing sugars, they must first tautomerize to aldoses. Galactose, glucose, and fructose, all typical dietary monosaccharides, are all reducing sugars.
Disaccharides are made up of two monosaccharides and are either reducing or nonreducing in nature. Non Reducing disaccharides, such as sucrose and trehalose, contain glycosidic linkages between their anomeric carbons, preventing them from converting to an open-chain form with an aldehyde group. Only one of the two anomeric carbons in reducing disaccharides like lactose and maltose is involved in the glycosidic bond, while the other is free and can convert to an open-chain form with an aldehyde group.
Non-reducing sugars are those that do not reduce Tollens Reagent or Fehling's Solution. Sucrose and all polysaccharides, for example.
Reducing Sugars are sugars that can reduce Tollen's Reagent and Fehling's Solution. They have a free aldehyde or ketone group on the carbon next to these groups, as well as a hydroxyl (OH) group on the carbon adjacent to these groups."
In the Tollens' or Benedict's tests, for example, the aldehyde functional group permits the sugar to serve as a reducing agent. Certain ketoses can undergo tautomerization to produce aldoses, and the cyclic hemiacetal forms of aldoses can open to disclose an aldehyde. Acetals, such as those present in polysaccharide bonds, are difficult to convert to free aldehydes.
Hence option C is correct.

Note:
For many years, Fehling's solution was employed as a diagnostic test for diabetes, a condition in which blood glucose levels are dangerously high due to a lack of insulin production (type 1 diabetes) or an inability to react to insulin (type 2 diabetes) . It is possible to measure the quantity of glucose in the blood or urine by measuring the amount of oxidising agent (in this example, Fehling's solution) reduced by glucose. This allows the appropriate quantity of insulin to be given to return blood glucose levels to normal.