90 THE CARBOHYDRATES 



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. 



Another way of identifying raffinose J is to add to the 

 solution a little decoction of fresh yeast, to act as nutriment, 

 and then to sterilize the solution ; a pure culture of top fer- 

 mentation yeast is then added to the solution and the fermen- 

 tation is allowed to proceed in a thermostat at 31; when it 

 is completed, the solution is boiled with animal charcoal, 

 filtered, and evaporated to a syrup ; the latter is then, while 

 still hot, poured into hot alcohol and on cooling it is filtered ; 

 the filtrate is then precipitated by mixing with !- vols. of 

 ether. After 24 hours the supernatant liquid is poured off 

 and the residual syrup, which consists of melibiose, is con- 

 verted into its osazone which is characterized by its crystalline 

 form and melting point i78-9. 



Finally, Neuberg II has proposed making use of emulsin for 

 the identification of raffinose. 



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



fBau: " Chem. Zeit.," 1894, 18, 1797; 1897, 21, 185; 1902, 26, 69. 

 % Ibid., 1897, 21, 185. Ibid., 1902, 26, 69. 



|| Neuberg: " Bioch. Zeitsch.," 1907, 3, 519 and 535. 



