Starch, a complex carbohydrate, is a common component in many foods such as grains, potatoes, and legumes. While these foods provide energy, the human body cannot directly utilize starch in its complex form. For the body to access this energy, starch molecules must be broken down into simpler sugar units. This transformative process relies on specialized biological catalysts known as enzymes.
The Key Enzyme: Amylase
Amylase is the primary enzyme responsible for breaking down starch. It belongs to a class of hydrolases, which break down compounds by adding water. Amylase targets and cleaves the alpha-1,4 glycosidic bonds that link glucose units within starch molecules, converting them into smaller carbohydrate units. Salivary and pancreatic amylase are the most prominent forms in the human body, playing sequential roles in digestion.
The Digestive Journey of Starch
The digestion of starch commences in the mouth with the action of salivary amylase. As food is chewed and mixed with saliva, this enzyme begins to hydrolyze starch into smaller polysaccharide chains, such as dextrins, and the disaccharide maltose. Salivary amylase functions optimally in the mouth’s neutral to slightly alkaline environment, with a pH range around 6.7 to 7.0.
Once swallowed, the food mixture travels to the stomach. The highly acidic environment of the stomach, with a pH typically between 0.8 and 3.5, rapidly inactivates salivary amylase, halting starch digestion in this organ. No significant carbohydrate breakdown occurs in the stomach itself.
The partially digested food then moves into the small intestine for the next stage of starch digestion. Here, pancreatic amylase, secreted by the pancreas, takes over the role of breaking down any remaining starch and the dextrins into maltose. Pancreatic amylase operates effectively in the slightly alkaline environment of the small intestine, which has an optimal pH of approximately 7 to 8.
From Starch to Energy
Following the action of amylase, maltose, the disaccharide produced from starch breakdown, requires further processing. In the small intestine, an enzyme called maltase completes carbohydrate digestion. Maltase is produced by the cells lining the walls of the small intestine. It specifically breaks down each maltose molecule into two individual glucose units.
Glucose is the simplest sugar the body can absorb. Once glucose molecules are produced, they are absorbed through the walls of the small intestine and enter the bloodstream. From the bloodstream, glucose is delivered to cells throughout the body, where it serves as the main source of energy. Cells use glucose to produce adenosine triphosphate (ATP), which powers nearly all cellular functions and daily activities.