64 



FOODS AND NUTRITION 



hydrogen, and oxygen, so combined that the hydrogen 

 and oxygen are ahvays in the same proportion as they 

 occur in water. 



Starch is found in all green plants in the form of gran- 

 ules and is frequently stored in the cells of grains, seeds, 

 and stems, as a reserve food supply for the plant. To two 

 of these plant storehouses, the potato and the corn, com- 

 merce is indebted for its market supply of the substance. 

 The principal characteristics of starch are its insolubility 

 in water, and its transformation to a sticky swollen mass 

 or paste by the addition of boiling water. It gives a blue 

 color when treated with a solution of iodine, and this 

 latter means is usually employed as a test to detect its 

 presence in foods. (See Ex. XIV.) 



There are several different kinds of sugars; cane sugar 

 or saccharose is the sugar of the market, and as its name 

 indicates is obtained from the juice of the sugar cane. It 

 is also obtained from the juice of the sugar beet. Grape 

 sugar or dextrose (also called glucose) is found in almost 

 all plant and animal tissues, and it derives its name of 

 grape sugar from its abundance in grapes. Still another 

 form is milk sugar or lactose, found in milk. Both sac- 

 charose and lactose can be changed to dextrose by boiling 

 with certain acids, notably, hydrochloric. This process is 

 called inversion. 



Grape sugar is characterised by two important prop- 

 erties, the power to ferment and the power to take up 

 oxygen. As a result of the first, certain substances, such 

 as yeast, are capable of breaking it up into alcohol and 

 carbonic acid gas; while to the second is due the means of 

 detecting its presence in foods. The most common test 

 used is a mixture called Fehling's solution. (See Ex. XV.) 



