Maltose is not starch, though the two molecules are chemically related as members of the carbohydrate family. Starch is classified as a complex carbohydrate, a very large molecule designed for energy storage in plants. Conversely, maltose is known as a simple sugar, a much smaller molecule that acts as an intermediate form of energy. The distinction between them lies entirely in their size and structural complexity.
Starch: The Complex Carbohydrate
Starch is a polymeric carbohydrate, which means it is a large molecule made up of many repeating smaller units. Specifically, starch is a polysaccharide built from a massive number of glucose molecules linked together in long chains. This structure makes starch a complex carbohydrate, and its chemical formula is often represented as (C₆H₁₀O₅)n, where ‘n’ signifies the high number of glucose units involved.
The structure of starch is not uniform; it consists primarily of two types of molecules: amylose, which forms long, linear chains, and amylopectin, which is highly branched. Plants produce starch in their green leaves during photosynthesis, storing it as a reserve food supply in specialized organs like potato tubers, corn kernels, and wheat grains. This dense, complex form allows plants to store energy efficiently.
Maltose: The Simple Sugar
Maltose is an organic compound known chemically as a disaccharide, meaning its structure is composed of only two sugar units. These two units are both molecules of glucose, joined together by a specific bond known as an alpha-1,4-glycosidic linkage. This small size is why maltose is classified as a simple sugar, in stark contrast to the massive polymeric structure of starch.
The common name for maltose is “malt sugar,” which comes from its frequent appearance during the malting process. When cereal grains, most notably barley, are germinated for brewing, enzymes within the grain break down their stored starch into maltose. Maltose is also found naturally in various sprouted grains and is known for being mildly sweet, less so than table sugar.
The Relationship Between Starch and Maltose
The relationship between starch and maltose is one of precursor and product, which explains why there is often confusion between the two substances. Maltose is produced when the large starch molecule is broken down, or hydrolyzed, into smaller fragments. This process is carried out by enzymes, such as amylase, which is present in human saliva and the pancreas.
Amylase acts on the long chains of starch, cleaving the chemical bonds to release fragments, with maltose being the primary two-unit product. This breakdown is necessary because the enormous starch molecule is too large to be directly absorbed by the body in the small intestine. Once starch is reduced to maltose, the body employs a separate enzyme, maltase, to split the disaccharide into its final component: two individual glucose molecules.
Only these single glucose units are small enough to pass through the intestinal wall and enter the bloodstream to provide energy. The difference in size is therefore the functional distinction, as starch is the storage form of energy, and maltose is the immediate, digestible sugar released during the initial stages of that energy’s liberation.