48 FEUITS AND FRUIT PEODUCTS. 



all the other fruits the relative amount was much larger, and in case of 

 the strawberry the juice contained only one-fifth of the amount present 

 in the whole fruit. This point is of value in the examination of jellies 

 where the use of gelatin as a gelatinizing agent is suspected. The 

 average content of protein in 14 samples of jellies (see Table 19) pre- 

 pared in the laboratory was 0.215 per cent, and the extremes were 0.1:18 

 per cent and 0.069 per cent; and of 19 pure samples bought on the 

 market the average content of protein was 0.205 per cent and the 

 extremes 0.312 and 0.112 per cent. The use of gelatin would raise 

 the protein content far above the normal. 



Sugars.— The sugars normally present in the fruits are dextrose, 

 levulose, and cane sugar. As is indicated b}^ the polarizations made 

 at 86^, dextrose and levulose are present in nearly equal proportions; 

 frequently there is an appreciable excess of levulose, but seldom an 

 excess of dextrose. Cane sugar is an extremely variable factor, and 

 may range from none in many of the samples reported to several per 

 cent. As a general rule, the large fruits, such as the apple, pear, 

 peach, plum, and orange, have a much higher content of cane sugar 

 than the small fruits, such as the strawberry, raspberry, blackberry, 

 and currant. In apples Colby reported an average of 4.59 per cent, a 

 maximum of 7.79 per cent, and a minimum of 1.80 per cent; Browne 

 reported an average of 3.99 per cent, a maximum of 6.81 per cent, and 

 a minimum of 1.74 per cent, while Richards gives 1.53 per cent as 

 the average and limits of 2.81 per cent and 0.15 per cent. In oranges 

 Colby gives an average of 5.25 per cent and limits of 6.75 per cent 

 and 4.80 per cent, and results reported for oranges, plums, peaches, 

 and pineapples are also high. 



Stone found, in 20 samples of strawberries, the average percentage 

 of cane sugar to be 0.58, the maximum 1.17, and the minimum 0.02. 

 In this laboratory an average of 0.46 per cent was found in the same 

 fruit; in blackberries, 0.16 per cent; cherries, none; currants, none; 

 black raspberries, none, and red raspberries, 0.80 per cent. Results 

 given in Tables 14 and 15 also verify the general statement. 



Polarization. — Table 13 gives the polarizations of a number of pure 

 fruits and fruit juices, together with the content of reducing and cane 

 sugars. The cane sugar was calculated from the polarizations by the 



Clerget formula, S= ^,^ ^ — . Here all the large fruits except the 



J. "XT: 2 



apple and the pear show a dextrorotatory direct reading, while all 

 the small fruits show a levorotatory direct reading. The invert 

 readings at room temperature were all negative with the single excep- 

 tion of the plum, which also has a positive reading at 86°, indicating 

 an excess of dextrose over levulose. The polarizations on all the other 

 samples indicated either a mixture of equal parts of dextrose and 

 levulose, or an excess of levulose. There is no direct relation between 



