44 



CARBOHYDRATES 



Table 3-4 



Cost of food calories as provided by various low-cost foods 



Price per Calories per - Cost per 100 



Food pound [cents] * pound calories [cents] 



Potatoes 5 377 1.32 



Bread, white 14 1250 1.12 



Macaroni 17 1710 1.00 



Rice 15 1670 0.90 



Beans, dry 13 1530 0.85 



Flour, patent 9 1650 0.55 



Sucrose 10 1750 0.57 



* Retail prices at Madison, Wisconsin, January, 1952. 



The chemical constitution of sucrose is expressed by the following 

 formula: 



H,COH 



0. j^ H2COH ^O^ H2COH 



H OH OH H 



a-GIucoside part ^-Fructoside part 



Sucrose 



Note that the disaccharide linkage is a,(3-l,2 and involves the original 

 reducing groups of each of the component simple sugars. Hence sucrose 

 does not reduce Fehling's solution or give an osazone with phenylhydra- 

 zine. It is fermented by yeast and by most bacteria. Strictly speaking, 

 sucrose is not fermented because it is first hydrolyzed; the resulting 

 glucose and fructose undergo the fermentation. Likewise, in the utiliza- 

 tion of sucrose by the body, hydrolysis precedes absorption. 



Sucrose may be estimated either by chemical means or through the 

 aid of a saccharimeter.^ (See optical rotation.) If reducing sugar is 

 determined before and after hydrolysis, the increase in reducing sugar 

 furnishes a means of calculating sucrose. Since a molecule of water is 

 added during the hydrolysis, 95 per cent of the invert sugar (increase 

 in reducing sugar) is equivalent to the sucrose in the sample. For 

 €xample: 



per cent 



Reducing sugar before hydrolysis 4.36 



Reducing sugar after hydrolysis 9.28 



Invert sugar 4.92 



Sucrose, .95 X 4.92 4.67 



^ This is a polarimeter especially calibrated to read percentage of sucrose in the 

 solution tested rather than the angle of rotation of the polarized light. 



