FOODSTUFFS 55 



by the action of ferments or by boiling with dilute acids the 

 most important of the cleavage products are various amino-acids. 

 The different proteins differ quantitatively and qualitatively 

 as regards the number and kinds of amino acids liberated. 

 Thus, serum albumin and egg albumin yield no glycocoll, while 

 it is constantly present among the cleavage products of serum- 

 globulin. Leucin is present to the extent of 20.5 per cent, 

 in horse's serum albumin, while egg albumin yields only 7.1 

 per cent. Gelatin, which yields 16.5 per cent, of glycin, gives no 

 tyrosin or tryptophan at all, while egg albumin and serum albu- 

 min yield tyrosin in different amounts. The process by which 

 the protein molecule is decomposed is called hydrolysis. The 

 molecules take up water and split into smaller molecules. 

 This takes place in various stages, bodies like acid-, or alkali- 

 albumin, being first formed, then proteoses, then peptones. 

 The latter are further split into bodies containing a relatively 

 small number of amino-acids linked together. These bodies 

 are called polypcptids and are ultimately broken up into individ- 

 ual amino-acids. The synthesis of amino-acids into increasingly 

 complex polypeptids has been accomplished until bodies giving 

 the characteristic reactions of peptones have been obtained. 



Carbohydrates. As regards chemical constitution, the simplest 

 carbohydrates are aldehydes or ke tones, ife., they are the first 

 oxidation products of primary and secondary alcohols respec- 

 tively. The sugars containing six carbon atoms are termed 

 hexoses. Examples: dextrose, levulose, and galactose. The 

 empirical formula of these three is the same (C 6 H 12 O 6 ), but 

 owing to the different arrangement of the atoms or groups of 

 atoms they have each their own characteristic properties. 

 Dextrose rotates the plane of polarization to the right, levulose 

 to the left. By the union of two molecules of a monosaccharide 

 with loss of a molecule of water, a disaccharide is formed. 

 Examples of the latter are cane sugar, maltose, and lactose, 

 each with the same empirical formula (C 12 H 22 O 11 ). Cane sugar 

 yields on hydrolysis equal parts of dextrose and levulose; 

 lactose yields dextrose and galactose; while maltose is con- 

 verted into dextrose. By the condensation of more than two 

 molecules of monosaccharides, polysaccharides are formed, 

 such as starch, dextrin, and glycogen. Their general formula 

 is written (C 6 H 10 O 5 ) n ; the value of n may be several hundred. 



