CARBOHYDRATES IOI 



the dextrose and levulose yielded on inversion probably being united 

 together by the aldehyde and ketone radicals, respectively. Similarly, it does 

 not form an osazone. In strong solutions, saccharose acts as a food pre- 

 servative against bacterial or other decomposition through organic agencies. 

 On boiling with dilute mineral acids or through. the action of inverting en- 

 zymes, one molecule of saccharose yields one molecule of dextrose and one 

 molecule of levulose,. 



Lactose (milk-sugar) is present as the chief carbohydrate of milk. It 

 may be separated from the whey the product remaining after skimming 

 milk and precipitating the proteins therein. It can be prepared in large 

 hard crystals. It is much less soluble in water than cane-sugar, and has but 

 a slightly sweet taste. Lactose is strongly dextrorotatory, [a] d = +52.5. 

 It reduces alkaline copper solution and forms a characteristic osazone. It 

 is not fermented by ordinary yeast; certain bacteria easily convert it into 

 lactic and other simple organic acids. The inverted milk-sugar undergoes 

 alcoholic fermentation readily, and kumiss and kephir, made from mare's 

 and cow's milk, respectively, are prepared in this way. On hydrolyzing by 

 boiling with mineral acids or through the action of inverting enzymes, the 

 lactose is split into dextrose and galactose. 



Dextrins are a series of intermediate poly-saccharides between the di- 

 saccharides and the starches. They are non-crystalline, are soluble in 

 water, and are precipitated on the addition of alcohol in excess. They are 

 dextrorotatory and are not fermented by yeast. Their power to reduce 

 alkaline copper solution has been questioned, but they yield osazones which 

 are relatively soluble. They have a slightly sweet taste. The more com- 

 plex dextrins give a red reaction with iodine. 



Starch is found in various parts of plants, especially in the tubers and 

 seeds. It is a form of storage carbohydrate, and serves as a source of ma- 

 terial for the development of the young plant. Starch is obtained commer- 

 cially from potatoes, rice, corn, and wheat. It constitutes the greater pro- 

 portion of our food. 



Starch as obtained is a soft white powder which on microscopic examina- 

 tion is found to consist of small granules. These are often characteristic in 

 shape and size according to the origin of the material. The granules appear 

 to be built up of concentric layers. They are covered with a sheath of 

 starch cellulose. This sheath is ruptured by boiling the aqueous suspension 

 of starch granules and an opalescent solution or starch paste is obtained. 

 On standing in dilute solution, the opalescent material settles to the bottom, 

 but the clear fluid above still gives the blue reaction w r ith iodine. This 

 color is characteristic for starch; it disappears on heating, but returns when 

 the liquid cools. Starch will not diffuse through a semi-permeable mem- 

 brane. On boiling with dilute mineral acids starch is hydrolyzed to dex- 

 trose. The dextrins and maltose are formed as intermediate products. 



