TRISACCH ARIDES 1 2 3 



It is strongly dextro-rotatory, a^ — + 104-4°, in 10 per cent 

 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. 



^18^32016 + HgO = CgHj^Og -{- CijHjg^ii 

 Raffinose Levulose Melibiose 



On heating further the melibiose itself is broken up as 



follows : — 



CjjHgjOn + HjO = CjHijOg + CgHijOg 

 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. 



From its behaviour on hydrolysis the constitution may be 

 represented by the formula J : — 



. o . . o- 



HOCH2 .CH . {CHOH)2— "C O— CH— (CHOH)2— CHOH— CH— CHj— O— CH— (CHOH)3— CH— CHtOH 



CH3OH • 



Fructose. Glucose. Galactose. 



* Neuberg : " Biochem. Zeit.," 1907, 3, 519. 



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



t Haworth, Hirst, and Ruell : " J. Chem. Soc," 1923, 123, 312.5. 



