CARBOHYDRATES – PROPERTIES AND FUNCTIONS.ppt
- 1. Mrs. R.Subha, M.Sc., M.Phil., D.C.T., Assistant Professor of Home Science
- 2. Carbohydrates are essentially substances that are made up of carbon, hydrogen and oxygen only. The carbohydrates are divided into three broad categories, namely, monosaccharides, oligosaccharides and polysaccharides. Monosaccharides represent the group of carbohydrates that cannot be further hydrolyzed to smaller molecules. They form the building blocks of the more complex carbohydrates. Oligosaccharides comprise the low molecular weight polymers that include the disaccharides and trisaccharides and compounds with as many as ten monosaccharides linked into single molecules.
- 3. Polysaccharides are the carbohydrates which contain more than 10 monosaccharide units.They can be hydrolyzed into hundred or even thousands of monosaccharide units. The suffix –ose in sugar is changed to –ans to describe the corresponding polysaccharide. Examples: (1) Pentosans (a)Arabans (b) Xylans (2) Hexosans (a) Glucans à starch, dextrin, glycogen, cellulose, inulin (b) Mannans (c) Galactans (3) Complex polysaccharides (a) Pectins or pectic substances (b) Gums (c) Mucilages (d) Algal polysaccharides à Alginic acid and carrageenan. (e) Bacterial polysaccharides à Xanthan gum.
- 5. defined as polyhydroxy aldehydes or ketones and their derivatives. Their general formula can be represented as Cx(H2O)y. Carbohydrates are formed in plant cells from carbon dioxide and water in a process called as photosynthesis. 1 g of carbohydrates provide 4 kcal energy. In human food, the sources of carbohydrates are cereals, roots, tubers, sugarcane and sugarbeet. Carbohydrates are named according to sources from which they are obtained e.g., fructose (fruit sugar), lactose (milk sugar), xylose (wood sugar) and cellulose (from cell membrane).
- 6. Most of the monosaccharides, disaccharides and lower polysaccharides are sweet in taste, whereas starch and cellulose are tasteless. They exhibit stereoisomerism. Stereoisomers are compounds whose structural formula is same but arrangement of atoms in 3- Dimensional space is different. E.g., with respect to Carbon no. 5, Glucose has two forms, D-glucose and L-glucose.
- 7. They exhibit optical activity. (Optical activity is a phenomenon in which a molecule rotates plane of plain polarised light. If the molecule rotates the plane towards left, it is designated levo rotatory (- sign) and if the plane is rotated towards right, the molecule is designated dextro rotatory (+ sign). D-glucose rotates plane of plain polarised light towards right while L-fructose rotates it towards left.
- 8. The sugars in which free aldehyde or ketone groups are present can reduce Fehling’s solution and Benedict’s solution are called reducing sugars. The sugars in which free aldehyde or ketone groups are absent are called as non-reducing sugars. Glucose, fructose, lactose etc., are reducing sugars whereas sucrose is a non-reducing sugar.
- 9. They are a major part of total caloric intake. Starch and glycogen serve as temporary stores of glucose. Water insoluble carbohydrates are major components of cell wall in plant cells and cell membrane in animal cells. Carbohydrates function as lubricants in skeletal joints and help the cells to stick with each other and remain in place.
- 10. Satyanarayana U. & Chakrapani U. (2011), “Biochemistry”. Books and Allied (P) Ltd. pp. N. Shakuntala Manay & M. Shadaksharaswamy (2001), “Foods: Facts and Principles”. New Age International Publishers.