204 THE CARBOHYDRATES 



conversion of the insoluble pectose, or protopectin as it is 

 now termed, into soluble pectin, a change which he thought 

 was due to the hydrolytic action of the fruit acids. Evidence 

 has, however, been obtained to show that this change is due 

 to enzyme action.* That the middle lamella is not involved in 

 the earlier stages of this change has been shown by Carre, f 

 who found that the middle lamella pectic substance remained 

 at a constant level throughout the process of ripening, and it 

 was only in the over-ripe condition that the amount begins to 

 decrease and finally vanishes when, owing to the absence of 

 cementing material, the cells are entirely separated from one 

 another. In the absence of exact knowledge concerning the 

 nature of the relation between soluble pectin and proto- 

 pectin, it is not possible to be certain what happens when the 

 one is formed from the other. The view put forward by 

 Mangin $ that protopectin is a loose form of combination 

 between pectin and cellulose is supported by von Fellenberg, 

 who suggests that the production of soluble pectin from proto- 

 pectin involves hydrolysis of this compound ; the same con- 

 clusion has been arrived at by Sucharipa § ; possibly the 

 softening of fruit on ripening is due to this same separation 

 of soluble pectin from its combination with cellulose ; it is 

 only in the last stages of over-ripeness that still further 

 hydrolysis of the pectin would occur with consequent dis- 

 integration of the tissues as indicated above. 



Appleman and Conrad, || working on peaches, find that the 

 transformation of protopectin into pectin appears to be the 

 only pectic change during ripening and softening. The sum 

 of pectin and protopectin was practically constant at all 

 stages of ripening, but both constituents disappear slowly 

 in over-ripe peaches. 



The everyday significance of pectins as the basis of fruit 

 jellies and jams justifies a reference to their use in this con- 



* Thatcher : "J. Agric. Res.," 1915, 5, 103; Carre, "Ann. Bot.," 

 1925. 39» 811. 



t Carre : loc. cit. % Mangin : " Comp. rend.," 1888-1893. • 



§ Sucharipa : " J. Amer. Chem. Soc," 1924, 46, 145. 



II Appleman and Conrad : " Univ. Maryland Agr. Exp. St. Bull.," 

 283. July, 1926. 



