Polyphenolic Metabolites and Antioxidant Activities of Alpinia katsumadai Hayata. and Its Adulterants

The peels and seeds of Alpinia katsumadai and its adulterants A. henryi K. Schum. and A. blepharocalyx K. Schum. were comparatively analyzed for their chemical compositions. Targeted metabolomics based on liquid chromatography-mass spectrometry (LC-MS) identified a total of 1009 polyphenolic metabolites from these nine plant samples, including 485 flavonoids, 374 phenolic acids, 125 lignans and coumarins, 20 tannins and 5 others. Principal component analysis (PCA), orthogonal partial least squares-discriminant analysis (OPLS-DA), and hierarchical cluster analysis (HCA) revealed that the compositions and contents of polyphenols in each fruit part were similar between A. henryi K. Schum. and A. katsumadai, and the seeds and peels of A. blepharocalyx K. Schum. had similar polyphenolic composition. Quantitative analysis showed that the contents of alnustone, alpinetin, cardamonin, and pinocembrin were significantly higher in the seeds than in the peels. Notably, the contents of these four compounds in the seeds of A. henryi K. Schum. and A. katsumadai were ten to several tens of times higher than those of A. blepharocalyx K. Schum.. Pearson correlation analysis between antioxidant activity against free radicals and differential metabolites revealed that the strong 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity of the seeds of A. henryi K. Schum. and A. katsumadai was associated with their contents of alnustone and alpinetin, whereas the strong 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical of A. blepharocalyx K. Schum. was related to its isorhamnetin-3-O-rutinoside and cinnamic acid contents. The findings suggested that A. katsumadai and A. henryi K. Schum. seeds were rich in bioactive substances, with their contents of alnustone, alpinetin, cardamonin, and pinocembrin meeting the Chinese pharmacopeial specifications, and they exhibited potent antioxidant activity. A. katsumadai was superior to A. henryi K. Schum. and A. blepharocalyx K. Schum.. In contrast, A. blepharocalyx K. Schum. contained more unique polyphenolic substances, whose composition and functions warrant further investigation. This study provides theoretical guidance for the selection of high-quality Chinese medicinal materials and the development of related products.