218 TANNINS 



Tannin is not uncommon in unripe fruits, and the amount 

 of these astringent substances diminishes during ripening. 



According to Bassett* "the amount of tannin in fruits 

 varies with certain factors, such as injury, length of time be- 

 tween removal from tree and analysis, etc. The presence and 

 relative amount of this tannin or tannin-like body is con- 

 trolled by the presence of certain enzymes which vary in 

 amount and activity during the growth of these fruits." 



Buignet, from the fact of the diminution of tannin and 

 starch which occurs concurrently with the increase in sugar, 

 considered that the sugar in the ripe fruit (e.g. Musa) is 

 formed from these two substances. This opinion, however, is 

 not held by Gerber who investigated the same phenomenon. 

 In Diospyros Kaki he found the young fruit to be very 

 astringent, but riot so the ripe fruit. He considers that the 

 tannins disappear by complete oxidation without the forma- 

 tion of carbohydrates. One reason for his opinion is that in 

 the conversion of tannin into carbohydrate more carbon diox- 

 ide would have to be liberated than oxygen absorbed, where- 

 as in fruits the relation is the reverse. 



On the other hand, he does consider the tannins to be of 

 some value, for they, by the formation of pectins, may limit 

 the loss of carbohydrate. 



Further, inasmuch as the pleasing odours of fruit are ac- 

 quired after the tannin has disappeared it is not impossible 

 that the latter may have some connexion with the formation 

 of fruit esters. 



Other suggestions regarding the value of tannin are not 

 wanting; thus Moore f states that it may play an important 

 part in the lignification of cell walls. 



More recently Drabble and NierensteinJ have come to 

 the conclusion that tannins play an important part in cork 

 formation, and are acted upon in the plant by formaldehyde 

 and acids and are precipitated in the walls of the cork cells. 

 Reasons for this theory may be alluded to briefly. 



* Quoted from the footnote appended to a paper on the Toxicity of Tannin 

 by Cook and *Taubenhaus : "Delaware Coll. Agric. Exp. Station," Bull., 91, 

 1911. 



f Moore : loc. cit. 



Drabble and Nierenstein : " Biochem. Journ.," 1906, 2, 96, 



