CARBOHYDRATES 43 



saccharides are hydrolyzed, the products being fructose and melibiose; 

 further hydrolysis of the melibiose yields glucose and galactose. 



POLYSACCHARIDES, (C 6 H 10 5 )x 



In general the polysaccharides are amorphous bodies, a few, how- 

 ever, are crystallizable. Through the action of certain enzymes or 

 weak acids the polysaccharides may be hydrolyzed with the formation 

 of monosaccharides. As a class the polysaccharides are quite insoluble 

 and are non-fermentable until inverted. By inversion is meant the 

 hydrolysis of disaccharide or polysaccharide sugars to form monosacchar- 

 ides, as indicated in the following equations: 



(a) C 12 H 22 On+H 2 0-+2(C 6 H 12 6 ). 



(&) C 6 H 10 05+H 2 0-C 6 H 12 6 . 



STARCH, (C 6 HioOi 5 ) x 



Starch is widely distributed throughout the vegetable kingdom, 

 occuriing in grains, fruits, and tubers. It occurs in granular form, the 

 microscopical appearance being typical for each individual starch. 

 The granules, which differ in size according to the source, are composed 

 of alternating concentric rings of granulose and cellulose. Ordinary 

 starch is insoluble in cold water, but if boiled with water the cell walls 

 are ruptured and starch paste results. In general starch gives a blue 

 color with iodine. 



Starch is acted upon by amylases, e.g., salivary amylase (ptyalin) 

 and pancreatic amylase (amylopsin), with the formation of soluble 

 starch, erythro-dextrin, achroo-dextrins and maltose (see Salivary Diges- 

 tion, page 56). Maltose is the principal end-product of this enzyme 

 action. Upon boiling a starch solution with a dilute mineral acid a 

 series of similar bodies is formed, but under these conditions glucose 

 is the principal end-product. 



Soluble starch may be prepared by the action of dilute hydro- 

 chloric acid on ordinary starch for several weeks, or at higher tem- 

 peratures for a shorter period. By precipitation with alcohol this may 

 be obtained in a dry form readily soluble in cold water. 1 



EXPERIMENTS ON STARCH 



i. Preparation of Potato Starch. Pare a raw potato, comminute it upon a fine 

 grater, mix with water, and "whip up" the pulped material vigorously before 

 straining it through cheese cloth or gauze to remove the coarse particles. The 



1 Fernbach: Proceedings Stk Int. Cong. Appl. Chem., 13, 131, 1912. 

 Chapin: Jour. Ind. and Eng. Chem., 6, 649, 1914. 



