Abstract:

This study utilized germplasm lines of Psathyrostachys juncea with contrasting high and low crude protein （CP） content and determined the contents of 18 amino acids in the leaves. Through amino acid composition analysis and nutritional value evaluation， the aim was to elucidate the protein nutritional characteristics of the P. juncea germplasm lines， providing a basis for development and utilization of P. juncea as a high-quality forage resource. The hydrochloric acid hydrolysis method was employed， using an automatic amino acid analyzer to determine the content of 17 amino acids， while tryptophan content was determined separately by spectrophotometry. Parameters such as the ratio of essential amino acids （RAA）， score of ratio coefficient （SRC）， and essential amino acid index （EAAI） were calculated and compared with the Food and Agriculture Organization/World Health Organization （FAO/WHO） amino acid pattern and ideal protein standards to evaluate the nutritional value of P. juncea protein. The results showed significant differences in total amino acid content and essential amino acid content between high-CP and low-CP P. juncea germplasm lines. P. juncea leaves contained 10 pharmacologically active amino acids， with a total content exceeding 65%， indicating potential medicinal value. Most essential amino acid contents in both germplasm types were close to or exceeded the FAO/WHO pattern standards， except for lysine （Lys） and methionine+cysteine （Met+Cys）， which were below the standards. In high-CP germplasm lines， the ratio of essential amino acids to total amino acids （E/T） ranged from 40.55% to 42.04%， and the ratio of essential to non-essential amino acids （E/N） ranged from 68.21% to 72.52%. In low-CP germplasms， E/T ranged from 42.20% to 43.22%， and E/N ranged from 73.01% to 76.11%， both exceeding the FAO/WHO recommended values. The SRC values of high-CP germplasm lines （47.17-57.37） were significantly higher than those of low-CP germplasm lines （35.31-43.47）. The average EAAI of both germplasm lines was close to 1， indicating high protein quality in P. juncea. Overall， high-CP germplasm lines outperformed low-CP germplasm lines in terms of protein nutritional supply， while low-CP germplasm lines had a slight advantage in the proportion of essential amino acids. Met+Cys were the first limiting amino acids in both lines of P. juncea. High-CP germplasm lines exhibited superior overall performance in SRC and EAAI， with germplasm lines “578854-8” and “531828-17” showing outstanding amino acid composition and nutritional balance， making them important candidate materials for future quality improvement. This study demonstrates that P. juncea leaves possess a complete profile of amino acids， a reasonable composition， and high nutritional value， making them a high-quality protein forage resource worthy of further development. The findings provide scientific data to support utilization of P. juncea in animal diets and its genetic breeding.

Key words: Psathyrostachys juncea, amino acid composition, Food and Agriculture Organization/World Health Organization ideal protein standard, ratio coefficient of amino acid, essential amino acid index