Human Nutrition » Amylase and Carbohydrate Digestion

What you'll learn this session

Study time: 30 minutes

The structure and function of the digestive system
The role of enzymes in digestion, focusing on amylase
The process of carbohydrate digestion in the body
How different factors affect enzyme activity
The importance of carbohydrates in the human diet

Introduction to Human Digestion

Our bodies need to break down the food we eat into smaller molecules that can be absorbed into our bloodstream. This process is called digestion and it involves both physical and chemical breakdown of food. The digestive system is specially designed to carry out this important function efficiently.

Key Definitions:

Digestion: The process of breaking down food into smaller molecules that can be absorbed into the bloodstream.
Enzymes: Biological catalysts that speed up chemical reactions in the body without being used up themselves.
Amylase: An enzyme that breaks down starch (a complex carbohydrate) into maltose and eventually glucose.
Carbohydrates: Organic compounds made up of carbon, hydrogen and oxygen atoms, serving as a major energy source for the body.

🍛 The Digestive System

The human digestive system is a long tube that starts at the mouth and ends at the anus. It includes several organs that work together to break down food, absorb nutrients and eliminate waste. The main parts are:

Mouth: Where mechanical digestion begins through chewing and chemical digestion starts with salivary amylase
Oesophagus: A muscular tube that moves food from the mouth to the stomach
Stomach: Where food is mixed with digestive juices and broken down further
Small intestine: Where most digestion and absorption occurs
Large intestine: Where water is absorbed and waste is formed
Rectum and anus: Where waste is stored and eliminated

🔬 Types of Digestion

There are two main types of digestion:

Mechanical digestion: The physical breakdown of food into smaller pieces through processes like chewing and churning in the stomach.
Chemical digestion: The breakdown of food molecules into smaller, soluble molecules using enzymes. This is where amylase plays a crucial role in carbohydrate digestion.

Enzymes and Digestion

Enzymes are essential for digestion as they speed up the chemical reactions that break down food molecules. Each enzyme is specific to a particular substrate (the substance it acts on) and reaction.

How Enzymes Work

Enzymes have a specific shape that allows them to bind to their substrate. This is often described as a 'lock and key' mechanism, where the substrate fits into the active site of the enzyme like a key fits into a lock. Once bound, the enzyme can break specific chemical bonds in the substrate, converting it into products.

💪 Specificity

Each enzyme can only work on a specific substrate. Amylase can only break down starch, not proteins or fats.

🌡 Temperature

Enzymes work best at their optimum temperature. For human enzymes, this is around 37°C (body temperature). At higher temperatures, enzymes denature and stop working.

💧 pH

Each enzyme has an optimum pH. Amylase works best at a neutral pH (around 7) in the mouth, but is deactivated in the acidic environment of the stomach (pH 2).

Amylase and Carbohydrate Digestion

Amylase is one of the key digestive enzymes in the human body. It's responsible for breaking down starch, which is a complex carbohydrate found in foods like potatoes, rice, bread and pasta.

🍞 Carbohydrates in Our Diet

Carbohydrates are a major source of energy in our diet and come in several forms:

Simple carbohydrates (sugars): Include glucose, fructose and sucrose. Found in fruits, some vegetables and processed foods.
Complex carbohydrates (starches): Long chains of glucose molecules found in foods like bread, pasta, rice and potatoes.
Dietary fibre: Complex carbohydrates that cannot be digested by human enzymes but are important for digestive health.

📊 The Digestion Journey

Carbohydrate digestion begins in the mouth and continues in the small intestine:

Mouth: Salivary amylase begins breaking down starch into maltose
Stomach: Amylase is inactivated by stomach acid, so starch digestion pauses
Small intestine: Pancreatic amylase continues breaking down starch into maltose
Small intestine: Maltase breaks down maltose into glucose
Absorption: Glucose molecules are absorbed into the bloodstream through the wall of the small intestine

The Action of Amylase

Amylase is produced in two main places in the human body: the salivary glands (salivary amylase) and the pancreas (pancreatic amylase). Both types of amylase have the same function - to break down starch - but they work in different parts of the digestive system.

Practical Investigation: Testing for Starch and Sugar

In the laboratory, we can demonstrate amylase action using simple chemical tests:

Iodine test for starch: Iodine solution turns blue-black in the presence of starch. As amylase breaks down starch, this colour change disappears.
Benedict's test for reducing sugars: Benedict's solution turns from blue to brick-red when heated with reducing sugars like glucose. As amylase produces maltose and glucose, the test becomes increasingly positive.

By taking samples at different time intervals and testing them, we can track the progress of starch digestion by amylase.

Factors Affecting Amylase Activity

Several factors can influence how effectively amylase works in the body:

Temperature Effects

Like all enzymes, amylase activity is affected by temperature:

At low temperatures (below 20°C), amylase works slowly because molecules have less kinetic energy
Activity increases as temperature rises, reaching optimum at around 37°C (body temperature)
Above 40°C, the enzyme begins to denature as the bonds maintaining its 3D structure break
At temperatures above 60°C, amylase is completely denatured and inactive

pH Effects

The pH of the environment also affects amylase activity:

Salivary amylase works best at a slightly alkaline pH of around 7.0-7.5 (the pH of saliva)
In the acidic environment of the stomach (pH 1.5-3.5), salivary amylase is deactivated
Pancreatic amylase works best at pH 7.5-8.0 (the pH of the small intestine)

Case Study: Lactose Intolerance

While not directly related to amylase, lactose intolerance provides an interesting example of what happens when a digestive enzyme is missing or deficient. People with lactose intolerance lack sufficient lactase, the enzyme that breaks down lactose (milk sugar). When they consume dairy products, the undigested lactose passes into the large intestine where bacteria ferment it, causing symptoms like bloating, gas and diarrhoea. This demonstrates the importance of having the right enzymes for proper digestion.

Practical Applications

Understanding amylase and carbohydrate digestion has practical applications in our daily lives and in medicine:

🍳 Cooking and Food Processing

Cooking starchy foods makes them easier to digest because heat breaks down some of the starch molecules. Food manufacturers also use industrial amylases to:

Convert starch to sugar syrups in food production
Improve bread texture by breaking down some of the starch in flour
Create "pre-digested" foods for people with digestive problems

🏥 Medical Applications

Doctors may test amylase levels in blood or urine to diagnose certain conditions:

High blood amylase levels may indicate pancreatitis (inflammation of the pancreas)
Amylase supplements can help people with pancreatic insufficiency digest carbohydrates
Understanding carbohydrate digestion is crucial for managing conditions like diabetes

Summary

Amylase plays a crucial role in carbohydrate digestion, breaking down complex starch molecules into simpler sugars that our bodies can absorb and use for energy. The process begins in the mouth with salivary amylase and continues in the small intestine with pancreatic amylase. Various factors, including temperature and pH, affect how well amylase works. Understanding this process helps us appreciate how our bodies extract nutrients from the food we eat and how problems with enzyme function can affect our health.

🧠 Test Your Knowledge!