Disaccharides

Maltose Maltose is combination of glucose +glucose The 2 molecule of glucose are attached by 1:4 linkage. One molecule of glucose is bound through the hydroxyl groups of carbon atom No 1 of one of the molecules to the hydroxyl groups of carbon atom No 4 of the second molecule of glucose.

Maltose

Maltose It is the end product of digestion of starch by ptyalin and it is the chief sugar of malt. It is reducing sugar due to the presence of a free aldehyde group. It gives osazone test which splits on cooling. Molisch’s and Fehling tests are positive. It is dextrorotatory. It is fermented by yeast due to the presence of maltase enzyme

Maltose It is not sweeter than glucose or fructose. It hydrolyzed by maltase enzyme and dilute HCl. Maltose is present in germinating barely (malt sugar).

Lactose (milk sugar) It is composed of one molecule of glucose and one molecule of galactose.They are united in a glucosidic 1:4 linkage with a net result that the aldehydic group of galactose is destroyed while that of glucose remains free. It is only in animal origin. It gives +ve Molisch’s test, +ve reduction test and gives a specific osazone test splits on cooling.

Lactose It is optically active and it is dextrorotary. It appears in the urine of the lactating women. It is not fermentable sugar due to the absence of lactase enzyme. By conc. HNO3 it gives mixture of mucic and saccharic acids. Lactobacillus acidophillus bacteris changes lactose to lactic acid.

Lactose

Lactose fermentation Lactose Water Lactic acid Bacteria

Lactose If milk is exposed to atmosphere, souring happens and caseinogen is precipitated due to the acidity formed as a result of formation of lactic acid. It is hydrolyzed by lactase enzyme giving rise to glucose + galactose

Lactose intolerance Infants normally have the intestinal enzyme beta-D-glucosidase (lactase) that catalyzes the hydrolysis of lactose to its component monosachharides for absorption into the blood stream. Much of the lactose in any milk they drink moves through their digestive tract to the colon, where its bacterial fermentation produces large quantities of CO2, H2 and irritating organic acids which leads to painful digestive upset termed lactose intolerance.

Sucrose (cane sugar) It is formed of the union of one molecule of glucose and fructose in a way that both the aldehydic and ketonic groups are destroyed. Glucose Fructose Sucrose

sucrose It is the common sugar used at home. It is non-reducing sugar. It gives no osazone test.It is like all CHO gives +ve Molisch’s test. It is optically active and it is dextrorotary. On hydrolysis it gives equal amount of glucose and fructose. The whole solution after hydrolysis is inverted from being dextro to laevorotary. The enzyme hydrolysing sucrose is called invertase.

sucrose The equal mixture of glucose and fructose is called invert sugar. Honey is chiefly invert sugar and the presence of fructose is the cause of its greater sweetness. It is fermented by yeast It is present free in cane sugar, carrots and certain fruits.

Trisaccharides It is composed by the union of 3 molecules of monosaccharides (raffinose). (glucose+ galactose+ fructose) with the elimination of 2 molecules of water. It is present in cotton seed oil and some cereals. It is non reducing sugar and it is dextrorotary. On hydrolysis it gives mixture of glucose, galactose and fructose.

Raffinose, also called melitose, is a trisaccharide that is widely found in legumes and cruciferous vegetables, including beans, peas, cabbage, brussels sprouts, and broccoli. It consists of galactose connected to sucrose via a 1α→6 glycosidic linkage. Humans cannot digest saccharides with this linkage and the saccharides are fermented in the large intestine by gas-producing bacteria.

Raffinose

Polysaccharides (glycans) Polysachharides Homopolysachharides Glucans Polymers of glucose Galactosans Polymers of galactose Heteropolysacchrides

polysaccharides All polysaccharides are formed of a great number of monosaccharide. All polysaccharides are non reducing sugar. Optically active. It gives negative Fehling and Bendict tests. It gives negative osazone test.

The monosaccharide entering in the formation of polysaccharides are attached together in glucosidic linkage (1:4 or 1:6). They form long chains which may be linear form as in case of cellulose or branched structures as in glycogen and starch. Some members give violet or blue color with iodine solution. Some are soluble in hot water, starch and some are insoluble as cellulose.

Classification of polysachharides Pentosans Formed by condensation of pentoses, araban and xylan Hexosans Glucosans (starch,cellulose,glycogen,dextrin) Fructosans (inulin). Mixed polysachharides Complex polysaccharides (pectin,heparin, Hyaluronic acid

Starch granules are formed from It represents the reseve food in plants Insoluble in cold water,it is soluble in hot water. Starch granules are formed from Amylose Amylopectin

Starch molecule

starch

starch Amylopectin: present in the outer layer of the granule.The molecule of amylopectin is branched. The branch is formed about 25glucose units. The glucose unit are linked together by alpha glucosidic 1:4 linkage,the linkage between the branches is through 1:6 glucosidic linkage. Amylose: forms the inner layer of the granule. The molecule of amylose is formed of very long chains of glucose which may reach about 300 units.

Other polysachharides includes dextrins,dextran,glycogen cellulose, inulin and hemicellulose and pectins.