NONPROTEIN NITROGEN CONTENTS OF ANIMAL AND PLANT FOODS

Nonprotein nitrogen (NPN) was extracted from 20 primary food products and purified by constant-volume ultrafiltration (10 000 MW cutoff) before separation and quantification of free and acid-hydrolyzable amino acids (AA) and their amides. Animal, fish, and poultry products contained 0-35 mg, cereal and pulse grains had 12-44 mg, and roots, vegetables, and fruits contained 65-240 mg of NPN/g of N. Free AA constituted one-third and half of total hydrolyzable AA in the animal and plant foods, respectively, and 70-90% of NPN was composed of non amino acid nitrogen. Glu/Gln and Asp/Asn were prominent in most free AA and peptide fractions, and Lys was a major AA in the free AA pool. © 1990, American Chemical Society. All rights reserved.