What is the Difference Between Reducing Sugar and Starch?

The main difference between reducing sugars and starch lies in their structure and properties. Here are the key differences:

1. Structure: Reducing sugars can be monosaccharides or disaccharides, while starch is a polysaccharide. Monosaccharides and disaccharides have a hemiacetal group with a free aldehyde or ketone group, which allows them to act as reducing agents. Starch, on the other hand, is a highly branched and organized polymeric carbohydrate made from amylase and amylopectin and lacks a free aldehyde or ketone group.
2. Reducing Properties: Reducing sugars can reduce other substances and then oxidize themselves due to their free aldehyde or ketone group. Starch, as a non-reducing sugar, cannot reduce other substances as it does not possess any free aldehyde or ketone group.
3. Types of Reducing sugars: Most monosaccharides, such as glucose, fructose, and galactose, are reducing sugars. Some disaccharides, like lactose, cellobiose, and maltose, are also reducing sugars.
4. Detection: Reducing sugars can be identified using tests like Tollens' test or Benedict's test.

In summary, reducing sugars are monosaccharides or disaccharides with a hemiacetal group that allows them to act as reducing agents, while starch is a polysaccharide without such a group and acts as a non-reducing sugar.

Comparative Table: Reducing Sugar vs Starch

The main difference between reducing sugars and starch lies in their structure and reactivity with other compounds. Reducing sugars can be monosaccharides or disaccharides, while starch is always a polysaccharide. Here is a comparison table highlighting the differences between reducing sugar and starch:

Reducing sugars contain free aldehyde or ketone groups, which allow them to transfer hydrogen electrons to other compounds and cause the reduction of other compounds. Common reducing sugars include glucose, galactose, fructose, and lactose (monosaccharides) and maltose (a disaccharide). On the other hand, non-reducing sugars, such as sucrose (table sugar), do not contain free aldehyde or ketone groups and are not capable of reducing other compounds. Starch is a polysaccharide composed of multiple glucose units and does not react with Benedict's or Fehling's tests, which are used to detect the presence of reducing sugars.