Bitter Pit in Afrples 19:^ 



Although tannic acid (in the concentrations with which we ar& 

 concerned, when dealing witli apple tissue or juice) does produce 

 a slight cloudiness in a 1% filtered starch solution, this does not 

 render the starch any less readily digested by diastase. With the 

 weaker tannic acid solutions (as Prof. Ewart points out) the cloudi- 

 ness vanishes at .35° C. 



In fact, with tlie taka diastase (Merck) in the possession of the 

 laboratory, the presence of small amounts of tannic acid caused 

 an acceleration of the enzyme action, and a slowing was only ob- 

 tained when the tannic acid concentration was approximately five 

 times as great as in apple juice. 



It proved a most fortunate circumstance for us that the taka 

 diastase preparation in our possession (the same as that used by 

 Greenwood and Rothera) showed this acceleration, for it permitted 

 us to show that (at least for the tannic acid concentrations up tO' 

 .25%) tannic acid does not foi-m a starch compound of less digesti- 

 bility, and that where it does inhibit diastatic action it does sO' 

 by precipitating the enzyme as suggested by Payen.i 



Solutions of the taka diastase in our possession gave no imme- 

 diate precipitate with dilute tannic acid, but in some of our ex- 

 periments, in which a weak enzyme solution was used, a precipitate 

 did form after two hours, and w^as accompanied by a slowing of 

 the rate of action. 



This slowing apparently depended upon the flocculation of the 

 enzyme per se, and was not proportional to the amount of tannic 

 acid present. In fact, a slightly greater amount of tannic acid 

 produced less slowing, probably because the accelerating factor was 

 present simultaneously. 



Careful tests were made in order to be certain that the tannic 

 acid acceleration was not due to an influence exerted upon the 

 starch iodine colour. 



Greenwood and Rothera used strong solutions of taka diastase, 

 and in the light of present results the very small amount of tannic 

 acid extracted from healthy apple pulp, or pitted cells, could only 

 have had a slight accelerating influence. 



With the malt diastase (Merck) (the same preparation as that 

 used by Greenwood *ind Rothera) tannic acid solutions, even when 

 dilute, always gave a precipitate, with solutions of the enzyme, 

 accompanied by a retardation of action. In Greenwood and 

 Rothera's experiments with malt diastase, accelerations were 



1. Quoted from Cza)v o Rionhemie dei- Pflanzeii, vol. i., p. .•i4.5 



