THE CHEMICAL COMPOSITION OF AQUATIC MACROPHYTES. II. AMINO ACID COMPOSITION OF THE PROTEIN AND NON-PROTEIN FRACTIONS

Abstract

The amino acid profile, crude protein (N × 6.25) and true protein (sum of all amino acids) levels were investigated in washed samples of several species of aquatic plants. There were differences of as much as 6% in the levels of crude protein and true protein of some of the species analyzed. Glutamic acid, aspartic acid and glycine, among the non-essential amino acids, and leucine, lysine, arginine and valine among the essential amino acids were major contributors to proteins in these plants. Levels of essential amino acids in the plants under investigation compared favorably with the FAO reference pattern and leaf protein concentrate. The non-protein nitrogen (NPN) and free amino acids (FAA) remaining in solution following the precipitation of protein using 80% ethanol, 5% TCA or 10% TCA were also determined in four species. Less total NPN remained in solution following ethanol extraction than when either 5 or 10% TCA was used. In addition to amino acids normally occurring in protein, ornithine, citrulline, asparagine, glutamine and -γ-amino butyric acid were also present in the NPN fraction. The FAA content ranged from approximately 6.6 to 16.8% of the total NPN, depending upon species of plant and method of extraction. The analysis indicated that this fraction could be nutritionally utilized by monogastric animals.