Analysis of Amino Acid and Derivative Diversity and Antioxidant Capacity in Ophiocordyceps sinensis and Its Substitutes

In this study, we used liquid chromatography–tandem mass spectrometry (LC-MS/MS) combined with multivariate statistical analysis to conduct comprehensive qualitative and quantitative profiling of amino acids and their derivatives in wild Ophiocordyceps sinensis (O. sinensis) samples from Naqu (NQ) and Xiaojin (XJ), cultivated O. sinensis (RG), and Bailing Capsules (BL). The objective was to systematically characterize amino acid metabolism and assess its correlation with antioxidant functionality. A total of 82 amino acids and their derivatives were identified. XJ had the highest essential amino acids, while BL had significantly lower content (except lysine) (p < 0.05). Antioxidant assays revealed that NQ and XJ samples exhibited superior antioxidant activity in 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonate) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and ferric ion reducing antioxidant power (FRAP) assays, and this activity showed a correlation to the contents of bioactive components such as total phenols (TPS), total polysaccharide (TPE), and total flavonoids (TF). Further pathway analysis using the Kyoto Encyclopedia of Genes and Genomes (KEGG) suggested that arginine and proline metabolism, aromatic amino acid biosynthesis, and tryptophan metabolism may be critical pathways that could underpin regional differences in O. sinensis quality, while variation in tyrosine metabolism may account for differences in antioxidant activity. This study provides a systematic comparison of amino acid profiles and antioxidant capacities across O. sinensis and its substitutes, offering a robust theoretical foundation for the development and functional evaluation of these bioresources.