238 



Alfred J. Eivart. 



'The diastase used jfave a faint reduction with Fehling's test. 



Even at optimal tempei'atures therefore tannic acid distinctly 

 retards diastatic action in a concentration of 0.0003 to 0.003 per 

 cent, (only 1-lOth of the starch having dissolved), strongly retards 

 it in concentrations of 0.003 to 0.06 (l-25th dissolved) and prac- 

 tically inhibits it in concentrations of 0.33 to 1 per cent. 



Tannic acid may therefore be regarded as a " coagulin," or 

 ■*' anti-diastase." Its inhibitory action appeal's to be much more 

 pronounced at 15-20O C. than at 35^ C. and the average tempera- 

 ture at which the metabolism of the apple takes place lies within the 

 former limits, ^sow, P. K. Scott found the sap of pitted Wolsely 

 apples contained 0.106, and that of clean apples 0.074 of tannic 

 acid per 100 c.c. of juice. At first sight we might seem to have 

 here an explanation of tlie non-solution of the starch grains in 

 bitter pit. 



The resistance of apple diastase to tannic acid has, however, 

 still to be determined. In addition the diastase of the pulp cells 

 is in their protoplasmic lining, whereas the tannic acid is in the 

 •cell-sap within. It is only when the protoplasm is killed that tannic 

 acid penetrates it, and there it comes into contact witli the oxi- 

 dase ferment, and is oxidized to a brown colour. The absence of 

 the latter so long as the cell is living shows that tlic diastase and 

 the oxidase ferments are not in contact witli tannic acid, altliough 

 the vacuolar membrane separating them may leprescnt a space 

 of less than a thousandth part of a millimetie. Furtlier there is 

 no evidence to show that tlie percentage of tannic acid is higher 

 prior to bitter pit formation, and an increased percentage of 

 tannic acid often follows as the result of injury or stimulation 



