Q.What are reducing and non–reducing sugars?

Maltose on hydrolysis yields two molecules of glucose.

Maltose (malt sugar) is a disaccharide composed of two D-glucose units joined by an alpha-1,4-glycosidic bond. Acidic or enzymatic (maltase) hydrolysis breaks this linkage to give two glucose molecules:

Maltose + H2O --> 2 Glucose …

Sucrose (table/cane sugar), a disaccharide of glucose and fructose, has the molecular formula C12H22O11.

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Sucrose hydrolyses to give one molecule each of glucose and fructose.

Cane sugar is sucrose, C12H22O11, a disaccharide made of an alpha-D-glucose unit and a beta-D-fructose unit joined by a glycosidic linkage.

Hydrolysis (acid or the enzyme invertase):

C12H22O11 + H2O -> C6H12O6 (glucose) + C6H12O6 (fructose)

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The glycosidic bond in sucrose links glucose's $C_1$ (anomeric carbon) directly to fructose's $C_2$ (its anomeric carbon), which is why sucrose has no free reducing group.

Glucose exists in its pyranose ring form with the anomeric carbon at $C_1$, and fructose exists in its furanose ring form with the anomeric carbon at $C_2$. In sucrose, these two anomeric carbons are joined directly to each other through a shared oxygen — an $\alpha(1\rightarrow2)\beta$ glycosidic linkage — rather than one anomeric carbon linking to a non-anomeric $-OH$ of the other sugar. Because both anomeric carbons are tied up in this linkage, neither sugar unit can open to expose a free aldehyde/ketone g …

Sucrose is a non-reducing disaccharide that on acid/enzyme (invertase) hydrolysis gives an equimolar mixture of glucose and fructose — never glucose alone.

Sucrose is formed by an $\alpha,\beta$-1,2-glycosidic bond between the anomeric carbons of $\alpha$-D-glucose (C1) and $\beta$-D-fructose (C2). Because both anomeric carbons are involved in the glycosidic linkage, neither ring can open to expose a free aldehyde/ketone — so sucrose is correctly described as a non-reducing sugar (d) and a disaccharide (b). On hydrolysis (dilute acid or the enzyme invertase) the glycosidic bond breaks to give glucose AND fructose (c is a true statement), n …