PECTINS 



201 



7. Pectins are insoluble in ammoniacal solution of copper 

 hydroxide (cuprammonia). 



Estimation of Pectins. 



The fact that pectins are readily saponified by caustic 

 soda has been adapted by Carre and Haynes * as a means 

 for their estimation. A dilute solution of the pectin is allowed 

 to stand with N/io NaOH overnight, and is then treated with 

 N acetic acid and after five minutes with M calcium chloride ; 

 the mixture is allowed to stand for an hour and is then boiled 

 for a few minutes and filtered ; the precipitated calcium 

 pectate is washed repeatedly until free from chloride and 

 weighed after drying at 100° C. The composition of the pre- 

 cipitate was represented as Ci7H220i6Ca, containing 7-66 per 

 cent of calcium ; but if the newer formula for pectic acid is 

 accepted, it would be C35H4^033Ca2, containing 7-45 per cent 

 of calcium. The method has been employed by Carre f for 

 investigating the changes which occur in the pectic constituents 

 of fruits during ripening. 



Action of Enzymes on Pectins. 



Pectase is the name given by Fremy to an enzyme which 

 he found was able to effect the coagulation of pectin solutions. 

 Pectases are very widely distributed in the plant world and 

 are found in the leaves of very many green plants ; the activity 

 of the enzymes from different sources is, however, not the same 

 as may be seen from the following table % giving the time re- 

 quired for gelatinizing a 2 per cent pectin solution 



Solanum Ivcopersicum . 



Vitis vinifera (fruit) 



Ribes 



Rheum, rhaponticum 



Marchantia polymorpha 



D uncus (mature) 



Delphinium 



Gitigko biloba 



4S hrs. 

 24 .. 

 15 .. 

 12 ,, 



2j „ 

 2 



T 1 



35 mins. 



Daucits (young) 

 Zea Mais 

 Iris florentina 

 Trifolium pratense 

 Medicago sativa 

 PI ant ago 

 Byassica napus 

 Lolium perenne 



15 mms. 



Less than 

 I min. 



* Carre and Haynes: " Biochem. Tourn.," 1922, 16, fio ; also Eramett 

 and Carre : id., 1926, 20, 6. 



t Carre : id., 1922, 16, 704 ; " .\nn. Bot.," T925, 39, 811. 

 t Bertrand and Mallevre : " Compt. rend.," 1S95, 121, 726. 



