Biochemical studies in the nitrogen metabolism of the apple fruit

Abstract

The high values obtained for amino N by the Van Slyke gasometric method in extracts of the peel and pulp of apple fruits were found due to the presence in them of tannin. A linear relation appeared between the amt. of tannic acid in pure solns. and the vol. of gas given in the Van Slyke detn. Removal of tannin by precipitation with caseinogen was quantitative only in the case of pure tannic acid solns.; in presence of apple extracts not more than 40% was removed. A method devised for removing tannin quantitatively from the apple extracts, prior to the Van Slyke detns., by precipitation with K dichromate at pH 3.2-5, did not interfere in any way with amino or amide groups present. Tentative suggestions are advanced for a new method for determining the tannin content of plant extracts based on Van Slyke amino N detns. before and after dichromate precipitation.