¾ Carbohydrates are defined as polyhydroxy aldehydes or polyhydroxy ketones or compounds that on hydrolysis produce either acetic acid and lactic acid. They are substances of universal occurrence and are much abundant in plants rather than in animals. ¾ Carbohydrates are grouped into two major classes: simple sugars (saccharides) and polysaccharides. Low molecular weight carbohydrtes are crystalline, soluble in water and sweet in taste; example glucose, fructose and sucrose. The high molecular weight carbohydrates (polymers) are amorphous, tasteless and relatievly less soluble in water; example starch, cellulose, gums, pectins, inulin etc. Bioses : Two carbon atom.
Trisoes: Three carbon atoms, but in the form of phospheric esters, eg: glyceraldehyde
Tetroses : Four carbon atoms eg: erythroses
Pentoses: hemicellulose, mucilage ad gums
Hexoses : six carbon atoms aldoses: glucose, mannose, galactose. ketoses: fructose and sorbose Carbohydrates which upon hydrolysis yield two molecules of monosaccharide are called as disaccharides.
Sucrose on hydrolysis gives glucose and fructose (sugarcane)
Maltose on hydrolysis gives glucose and glucose (malt sugar)
Lactose on hydrolysis gives glucose and galactose (cow’s milk) These liberate three molecules of monosaccharides on hydrolysis.
Raffinose on hydrolysis gives glucose , fructose and galactose.
Gentianose on hydrolysis gives two glucose molecules and fructose
Scillatriose , mannotrose , phanteose are the other examples. Stachyose , a tetrasaccharide, yields on hydrolysis , four molecules of monosaccharide. Indefenite number of monosaccharides.
Xylan is pentosan. Starch, inulin and cellulose are hexosans.
Polyuronides, gums and mucilages
Gums are pathological products conisting of calcium potassium and magnesium salts of complex substances known as “polyuronides”.
Mucilages are physiological products related to gums and they are generally sulphuricacid esters. A. NATURAL GUMS ` Sea weed gum-agar , algin , laminarin ` Plant exudates acac ia , tragacanth , karaya ` Seed gums guar gum , isapgol , tamarind ` Plant extracts pectin , larch , arabinogalactan ` Animal extract chitin
B. PREPARED GUMS ` Biosynthetic gums xanthan , dextrans ` Starch and its derivatives ` Cellulose derivatives 1. MOLICH’S TEST The test is positive with soluble as well as insoluble carbohydrates. It consist of treating the compounds with napthol and concentrated sulphuric acid which gives purple colour.
2. REDUCTION OF FEHLING’S SOLUTION To the solution of carbohydrate , equal quantity of fehling’s solution A and B is added. After heating brick red precipitate is obtained. 1. Acacia 2. Guar gum 3. Honey 4. Algin 5. Tragacanth 6. Pectin 7. Gum ghatti 8. Gum karaya 9. Ghitin 10. Isapgol 11. Psyllium 12. bael 11. Agar 12. Carrageenan 13. Manna 14. Inulin 15. Xanthan gum 16. Locust bean 17. Dextrins 18. Dextrans 19. Starch 20. Liquid glucose 21. Caramel 22. Arrow-root 23. Echinacea