Carbohydrates chemical structure

chemical structure and properties

1. CARBOHYDRATES - CHEMICAL STRUCTURE

2. INTRODUCTION Carbohydrates consist of the elements carbon ( C ), hydrogen ( H ) and oxygen ( O ) with a ratio of hydrogen twice that of carbon and oxygen.

3. MONOSACCHARIDES Number of Carbons Category Name Examples 4 Tetrose Erythrose, Threose 5 Pentose Arabinose, Ribose, Ribulose, Xylose, Xylulose, Lyxose 6 Hexose Allose , Altrose , Fructose, Galactose , Glucose , Gulose , Idose , Mannose, Sorbose , Talose , Tagatose 7 Heptose Sedoheptulose , Mannoheptulose

4. TETROSES D- erythrose D- Threose

5. Pentose D -Ribose D - Arabinose

6. HEXOSE- 6 carbons D- Gulose D- Idose

7. heptose   D - Sedoheptulose   D - Mannoheptulose

8. DISACCHARIDE Disaccharide Description Component monosaccharide sucrose common table sugar glucose 1α → 2 fructose maltose product of starch hydrolysis glucose 1α → 4 glucose lactose main sugar in milk galactose 1β → 4 glucose

9. Sucrose Lactose

10. Maltose

11. Polysaccharide- polymers of simple sugar Many polysaccharides, unlike sugars, are insoluble in water . Dietary fiber includes polysaccharides and oligosaccharides that are resistant to digestion and absorption in the human small intestine but which are completely or partially fermented by microorganisms in the large intestine .

12. Starch Starch is the major form of stored carbohydrate in plants. Starch is composed of a mixture of two substances: amylose , an essentially linear polysaccharide, and amylopectin , a highly branched polysaccharide. Amylose

13. Amylopectin : Amylopectin differs from amylose in being highly branched. Short side chains of about 30 glucose units are attached with 1α→6 linkages approximately every twenty to thirty glucose units along the chain. Amylopectin molecules may contain up to two million glucose units.

14. Glycogen Glucose is stored as glycogen in animal tissues by the process of glycogenesis . When glucose cannot be stored as glycogen or used immediately for energy, it is converted to fat.

15. Cellulose

16. Hemicelluloses

17. Properties of carbohydrates It is common for individuals to associate sugar (sucrose) with its inherent taste properties. Aside from providing a sweet taste and flavour , sugar imparts numerous functional properties that make it an important ingredient in many foods. Specific functional properties of sugar can be classified into four broad categories: sensory, physical, microbial and chemical

18. Sensory Properties Taste - Sweetness is generally the most recognized functional property of sugar. Caramelization - is a browning reaction that results from the action of heat on sugars. At high temperatures, the chemical changes associated with melting sugars result in a deep brown colour and new flavours . Flavour - Flavours result when tastes (sweet, sour, bitter, salty) are combined with sense of smell when food is consumed. Texture - Sugar makes an important contribution to the way we perceive the texture of food. For example, adding sugar to ice-cream provides body and texture which is perceived as smoothness.

19. Condi., Tenderizer - Sugar acts as an important tenderizing agent in foods such as baked products. During the mixing process, sugar compete with other ingredients for water. Maillard Reaction - results from chemical interactions between sugars and proteins at high heat. An amino group from a protein combines with a reducing sugar to produce a brown colour in a variety of foods (e.g. brewed coffee, fried foods, milk & breads ). Appearance - Sugar is responsible for the yellow-brown colours that develop in baked foods. Sucrose itself develops colour through caramelization .

20. Physical Properties Solubility - Sugar is easily soluble in water. The ability to produce solutions of varying sugar concentrations is important in many food applications. A high level of solubility, for example, is essential in beverages to provide sweetness and to increase viscosity to create a desirable ‘ mouthfeel '. Freezing Point - Sugar is effective in lowering freezing points. Freezing point depression is an important property in ice-creams, frozen desserts and freeze-dried foods to ensure the development of fine crystal structure and product smoothness . Boiling Point - The concentration of sugar in a solution affects the boiling point by raising it. This characteristic is important in candy manufacture as boiling point elevation allows for more sugar to be dissolved in solution, creating a ‘super saturated' and more concentrated solution.

21. Microbial Properties Preservation - Sugar plays a role in the preservation of many food products. The addition of sugar to jams and jellies, for example, inhibits microbial growth and subsequent spoilage. Fermentation - Sugar is extremely important in the baking and brewing industries. Yeasts use sugars as food to produce ethanol, carbon dioxide and water through the process of fermentation.

22. Chemical Properties Antioxidant Activity - Sucrose has been reported to exhibit antioxidant properties which help to prevent the deterioration of textures and flavours in canned fruits and vegetables. In addition, the products of the hydrolysis of sucrose (glucose and fructose) appear to have the ability to block the reactive sites of ions such as copper and iron and, to a lesser extent, cobalt. This characteristic of monosaccharides aids in food preservation by delay catalytic oxidation reactions.