Review of the nitrogenous constituents of the potato

Abstract

The potato has been a primary dietary constituent of modern civilizations. There may be some question about the relative role of the potato in the diet of certain medieval populations, such as the early South American Indians, but the importance of this foodstuff for centuries to inhabitants of Europe and the British Isles is a matter of record. Today the potato is still the most important vegetable for a large portion of the world's population. In spite of this historical background, the complete nutritional value of the potato has not been fully appreciated. The fact that starch constitutes two-thirds to three-fourths of its dry weight has directed our attention away from its important vitamins, minerals, and amino acids. Within the past two decades, it has been recognized that the potato is an important supplier of vitamin C. It was reported 25 years ago, however, that human adults were kept in nitrogen balance and in good health for as long as 5 months when fed diets consisting solely of potatoes and a small amount of fat (9, 12). This indicates that, with the possible exception of fat and fat-soluble indispensable nutrients, potatoes contain practically all essential dietary factors. It is the purpose of this paper to review the nitrogenous constituents of potatoes with particular emphasis on the nutritional value of the eight amino acids indispensable to man. Table 1 shows the range of nitrogen contents of several varieties of potatoes, reported by Neuberger and Sanger in 1942 (10). Total N ranged from 0.24 to 0.36 per cent of fresh weight. Our comparable analyses ranged from 0.20 to 0.42 per cent. On a moisture-free basis, the N values are 1.16-1.95 per cent. The percentage of N compounds can be estimated on a dry-weight basis by multiplying the 1.16 and 1.95 extremes by 6.25. In this case, the N-containing compounds comprise 7.2 to 12.2 per cent of the dry matter---or, let us say, 10 per cent for a general average. There is a rather wide variation in all these percentage N values.