RAFFINOSE 73 



solution, and consequently cane sugar in which raffinose occurs 

 as an impurity appears to contain more than 100 per cent of 

 sucrose when estimated polarimetrically ; hence raffinose is 

 sometimes known as " plus sugar ". 



It does not reduce Fehling's solution, nor does it react with 

 phenylhydrazine. 



On careful hydrolysis raffinose breaks up at first into levu- 

 lose and a disaccharide — melibiose. 



Raffinose Levulose Melibiose 



On heating further the melibiose itself is broken up as 

 follows : — 



CvjHagOii + H2O = CgHjoOu + CeHioO^ 

 Melibiose Dextrose Galactose 



If boiled with mineral acid, therefore, raffinose gives rise 

 to a mixture of dextrose, levulose and galactose. 



According to Neuberg,* raffinose is hydrolysed by emulsin 

 into cane sugar and galactose. (See below.) 



Raffinose, unlike cane sugar, is completely fermented by 

 bottom fermentation yeast to alcohol and carbon dioxide, 

 whereas top fermentation yeast is only able to ferment it parti- 

 ally, converting the levulose complex into carbon dioxide and 

 alcohol and leaving melibiose unattacked. These facts have 

 been made use of by Bau f for detecting and for estimating 

 raffinose. 



Detection. 



There are no rapidly performed characteristic tests for 

 raffinose. 



The only really reliable method of identifying it is to 

 isolate the substance by precipitating the strontium compound 

 in alcoholic solution, filtering off the precipitate and decom- 

 posing it by a current of carbon dioxide. The resulting 

 solution is then evaporated and the residue extracted with 

 alcohol to remove sucrose and other sugars which are more 

 soluble in alcohol than raffinose. The pure substance should 

 be identified by its crystalline form and optical properties. 



* Neuberg: " Bioch. Zeitschr.," 1907, 3, 519. 



fBau: "Chem. Zeit.," 1894, 18, 1797; 1897,21, 185; 1902,26, 6g. 



