4.1 Classification and structure of carbohydrates

Carbohydrates come in simple and complex forms. Simple carbs include single-sugar monosaccharides like glucose and fructose, and two-sugar disaccharides like sucrose and lactose. These provide quick energy and sweetness in foods.

Complex carbs have more sugar units. Oligosaccharides have 3-10 units and can act as prebiotics. Polysaccharides like starch and cellulose have many units, providing energy storage in foods and fiber for digestion.

Simple Carbohydrates

Monosaccharides

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• Simplest form of carbohydrates consisting of a single sugar molecule
• Glucose is the most common monosaccharide and primary source of energy for cells
  • Found in fruits, vegetables, and honey
  • Blood sugar refers to the concentration of glucose in the bloodstream
• Fructose is another common monosaccharide known as fruit sugar
  • Naturally occurs in fruits, vegetables, and honey
  • Sweeter than glucose and often used as a sweetener in processed foods (high fructose corn syrup)

Disaccharides

• Carbohydrates composed of two monosaccharide units joined by a glycosidic bond
• Sucrose, commonly known as table sugar, is a disaccharide made up of glucose and fructose
  • Produced by plants and extracted from sugar cane or sugar beets
  • Widely used as a sweetener in food products and beverages
• Lactose is a disaccharide found in milk and dairy products
  • Composed of glucose and galactose
  • Some individuals may be lactose intolerant due to a lack of the enzyme lactase needed to break down lactose

Complex Carbohydrates

Oligosaccharides

• Carbohydrates containing 3-10 monosaccharide units linked by glycosidic bonds
• Examples include raffinose (found in beans) and stachyose (found in soybeans)
• Some oligosaccharides, such as fructooligosaccharides, act as prebiotics promoting the growth of beneficial gut bacteria

Polysaccharides

• Carbohydrates composed of many monosaccharide units joined by glycosidic bonds forming long chains or branched structures
• Starch is a storage polysaccharide in plants consisting of amylose (linear) and amylopectin (branched)
  • Major source of energy in the human diet found in foods like potatoes, rice, and wheat
  • Amylose has a linear structure of glucose units linked by α-1,4 glycosidic bonds
  • Amylopectin has a branched structure with glucose units linked by α-1,4 and α-1,6 glycosidic bonds
• Cellulose is a structural polysaccharide in plant cell walls made up of glucose units linked by β-1,4 glycosidic bonds
  • Most abundant organic compound on Earth providing structure and support to plants
  • Humans lack the enzymes to break down cellulose, making it an important source of dietary fiber