The nitrogen of the potato

Abstract

The various nitrogenous fractions of the potato are estimated, mainly by the usual methods. Glutamine is determined by a new method, based on the loss of carboxyl carbon, as estimated by the ninhydrin method, on heating. The ninhydrin method is also used for estimation of a-amino-acid N, which is more reliable than the nitrous acid method. The indirect estimations are supported by the isolation of several nitrogenous substances, such as asparagine, glutamine, arginine and choline. Free histidine, lysine and cystine appear to be absent. Figures are given for a number of domestic vars., and the large variations noted in protein and in the relative proportion of the 2 amides, may be varietal characteristics. The N distribution over the tuber is not even. Thus the insoluble nitrogenous material is mainly present in the skin and cortex. Glutamine is mainly stored in the inner layers, whilst the outer layers are richer in asparagine.