42 PHYSIOLOGICAL CHEMISTRY 



nose may also be hydrolyzed by the enzyme raffinase, occurring in 

 certain bacteria and yeasts. 1 



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) Ci 2 H 22 Oii+H 2 O^2(C 6 H 12 6 ). 



(6) C 6 H 10 05+H 2 0->C6H 12 06. 



STARCH, (C 6 H 10 6 ) X 



Starch is widely distributed throughout the vegetable kingdom, 

 occurring 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, contain, 

 according to recent work, 2 at least three principal ingredients, 

 amylocellulose forming the cell walls, making up about 10 per cent 

 of the starch granules and not reacting with iodine; amylose, comprising 

 about 70 per cent of the granules and giving a blue color with iodine; 

 and amylopectin, the substance giving the high viscosity to starch 

 pastes, making up about 20 per cent of the granules, and giving no 

 color with iodine. 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 53). 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 at room temperature 

 or at higher temperatures for a shorter period. By precipitation with 

 alcohol this may be obtained in a dry form readily soluble in cold water. 3 



1 Kuriyama and Mendel: Jour. Blol Chem., 31, 125, 1917. 



2 Blake: Jour. Am. Chem. Soc., 38, 1245, 1916; 39, 315, 1917. Maquenne and Roux: 

 Ann. Chim. Phys., 9, 179, 1906. 



3 Fernbach: Proceedings 8th Int. Cong. Appl. Chem., 13, 131, 1912. 

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



