PECTINS 195 



Until some insight had been obtained into the chemical 

 nature of these substances, much confusion arose owing to the 

 tendency of different authors to describe identical products 

 under different names ; the following brief summary of the 

 development of the subject may help to clear the situation. 



Fremy, acting upon pectin with acids or alkalis, obtained 

 a number of intermediate products of hydrolysis to which he 

 gave the names of parapectin, metapectin, pectic acid, as well 

 as para- and metapectic acid ; many of those substances 

 were, however, insufficiently characterized and their existence 

 is no longer credited. 



Although the analyses by Tromp de Haas and Tollens * 

 of the pectins derived from a number of different sources 

 appeared to agree fairly well with the formulae (CgHioOgj^ or 

 2(C6Hio05) . HgO, Tollens f suspected that the pectins con- 

 tained carboxyl groups ; this view was finally shown to be 

 correct when the acidic nature of these substances was estab- 

 lished by Schryver and Haynes,J who prepared from pectin, 

 by alkaline hydrolysis, a pectic acid to which they assigned 

 the formula C17H24O16. 



Ehrlich § has shown that the residues from sugar beet re- 

 maining after the extraction of the sugar, provide a convenient 

 source for the extraction of pectin ; after washing with warm 

 water to remove soluble impurities, the residue is extracted 

 with boiling water and the filtrate after evaporation yields the 

 pectin, though, in all probability, not in the form in which it 

 occurred in the plant but partly hydrolysed as hydropectin 

 (see above) ; extracted with 70 per cent alcohol, it yields to 

 this solvent about 30 per cent of an araban or polymerized 

 arabinose, while the residue consists of a water-soluble pectin. 

 The fact that no araban is extracted by boiling beet residues 

 for some hours with 70 per cent alcohol indicates that in the 

 tissues the araban is combined with the water-soluble pectin, 

 and is only hydrolysed during the boiling with water. Acid 



* Tromp de Haas and Tollens : " Annalen," 1895, 286, 278. 

 t Tollens : id., 1895, 286, 292. 



t Schryver and Haynes : " Biochem. Journ.," 1916, 10, 539. 

 § Ehrlich : " Chem. Zeit.," 1917, 4»» ^97 : " Zeit. angew. Chem.," 

 1927, 40, 1305. 



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