20 FRUITS AND FRUIT PRODUCTS. 



sugar present may be readily ascertained from the polarizations and 

 from the per cent of solids. Use AUihn's method for the determina- 

 tion "" and express results as dextrose, making the calculation from 

 Allihn's tables. 



Owing to the varied nature of the reducing sugars found in fruits 

 and fruit products, and to the fact that no table has been constructed 

 that will in all cases apply, it was thought best to express all results 

 as dextrose, although it is well known that with pure invert sugar, as 

 well as with glucose products, a material error will arise. In no case 

 do we find that the reducing sugar is pure dextrose. With pure fruits 

 and fruit juices the reducing sugars are made up of practically equal 

 portions of dextrose and levulose. The same holds true with pure- 

 fruit products, in which the invert sugar of the fruit is greatly 

 increased by the inversion of the cane sugar by the organic acids pres- 

 ent. With fruit products containing glucose, on the other hand, the 

 problem is more complicated. Here is found not only invert sugar 

 from the fruit used, but also dextrose and maltose, which are normal 

 constituents of glucose sirups. If cane sugar were also used part may 

 become inverted and thus add to the invert sugar. Since the reducing 

 power of dextrose, levulose, and maltose vary widely, the expression 

 of reducing sugars as dextrose in case of mixtures of the three sugars 

 gives results far from the truth. The presence of cane sugar is also a 

 disturbing factor, as it materially influences the power of reduction, 

 depending upon the amount present. The quantity of invert sugar, 

 where no other sugar is present, can be determined from reduced 

 copper by reference to the table of Meissl and Wein.*" Wein*" has 

 constructed tables from results obtained by Meissl for the calculation 

 of reducing sugars in the presence of cane sugar from the amount of 

 copper reduced, but these tables hold good only with pure fruits or 

 pure-fruit products, and are not reliable when dealing with glucose 

 products. 



DETERMINATION OF DEXTRIN. 



Dissolve 10 grams of the sample'^ in a 100 cc flask; add 20 mg of 

 potassium fluorid and then about one-quarter of a cake of compressed 

 yeast. ^ Allow the fermentation to proceed below 25° C. for two or three 

 hours to prevent excessive foaming, and then place in an incubator at 

 a temperature of from 27° to 30° C. for five dsijs. At the end of that 



''V. S. Dept. of Agr., Div. of Chem. Bui. 46, revised, p. 35. 

 ^ Wiley, Principles and Practice of Agricultural Analysis, Vol. Ill, pp. 159-160. 

 '^ Tabellen zur Quantitativen Bestimmung der Zuckerarten. 



^ In the case of jellies 50 cc of a 20 per cent solution prepared as directed (p. 11) 

 may be used. 



''Bigelow and McElroy, Jour. Am. Chem. Soc, 1893, 15, 668, 



