chapter 3 charbohydrates

• carbohydrates are the sugars, starches, and fibers found in food.
• Primary source: Plants

  Stored as: Starches

  Main Function: Energy source for animals and humans
• Carbohydrates are composed of the elements carbon (C), hydrogen (H), and oxygen (O).
• Carbohydrates are classified as:

  • simple carbohydrates (sugars)
  • complex carbohydrates (starch, fiber, cellulose, glycogen)
• basic unit are called saccharides
• Simple carbohydrates:

  • monosaccharides (1 saccharides) - Triose(3C), Tetrose (4C), Pentose (5C), Hexose (6C)
  • disaccharides ( 2 monosaccharides) - maltose, sucrose, lactose, trehalose, palatinose
• Monosaccharides:

  • Triose (3C)- Glyceraldehyde
  • Tetrose(4C)- Eriythrose, Triose
  • Pentose(5C)-Xylose, Ribose, Arabinose
  • Hexose(6C)- Glucose, Galactose, Fructose
• Complex carbohydrates

  • Oligosaccharides (3 to 10 monosaccharides)
  • Polysaccharides (>10 monosaccharides)
• Polysaccharides:

  • Digestible: Plant starch (amylose, amylopectin), and animal starch (glycogen)
  • Indigestible: Fiber (cellulose, hemicellulose, pectin, gums, inulin)
• Each monosaccharide is linked together with a glycosidic bond.
• Saccharides (sugars) are low in molecular weight, soluble in water, and sweet to taste.
• Polysaccharides (complex sugars) are high in molecular weight, insoluble in water, and tasteless.
• Glyceraldehyde is a 3-carbon sugar (triose) that is a sweet colorless crystalline solid that is an intermediate compound in carbohydrate metabolism.
• Xylose which is 5-carbon sugar (pentose) can be catabolized or metabolized into useful products by a variety of organism
• • Maltose: glucose + glucose (form starch molecules, by-product of fermentation process)
  • Sucrose: glucose + fructose (found in sugar cane, sugar beets, honey)
  • Lactose: glucose + galactose ( called milk sugar)
• Oligosaccharides:

  • non-digestible: poorly digested in human gastrointestinal (GIT)systems, fermented by bacteria, causing flatulence
  • contain mostly non-reducing sugars
  • example: raffinose, stachyose, fructooligosaccharides
  • sources: dried beans, soybeans, peas, lentils
• Polysaccharides:

  • non-digestible or digestible
  • mostly non-reducing sugars
• Digestible polysaccharides:

  • starch: storage form of glucose in plants, food sources include grains, legumes, and tubers.
  • Glycogen: storage form of glucose in animals, stored in the liver and muscles

  Indigestible polysaccharides:

  • Fiber: - forms the support structures of leaves, stems, and plants
• Fiber:

  • Dietary fiber is the non-digestible part of plants (grains, seeds, legumes, fruit)
  • Functional fiber is a carbohydrate extracted from plants and added to food (cellulose, guar gum, pectin, psyllium)
• reducing sugar: sugar that contains aldehyde groups that are oxidized to carboxylic acids
• all monosaccharides are reducing sugars. they have a carboxyl group that donates an electron to a recipient
• maltose are reducing sugars because can free a carbonyl group
• sucrose can not free a carbonyl group so are non-reducing sugar. The glycosidic bond involves both anomeric carbons, thus, sucrose is not reducing sugar.
• Non-reducing disaccharides are named as glycosides, e.g. sucrose
• Oligosaccharides and polysaccharides are mostly non-reducing sugars.