Spatiotemporal Heterogeneity Analysis of Metabolome and Antibacterial Activity of Essential Oil from Alpinia hainanensis K. Schum. Fruits

This study examined the yield, metabolome and antibacterial activity of the essential oil from the fruit peel (P1, P2 and P3) and seed (S1, S2 and S3) of Alpinia hainanensis K. Schum. at different maturation stages (29, 47, and 73 days after bloom (DAB)). The seeds at the three maturation stages were green, light brown and dark brown in color, respectively. The essential oil, extracted by supercritical CO2 extraction, was analyzed qualitatively and quantitatively by gas chromatography-mass spectrometry (GC-MS) based on retention index (RI). The obtained data were analyzed by multivariate statistical analysis. Finally, the potential quality markers for the antibacterial activity were identified by spectrum-effect relationship analysis. The results showed that the oil content of the seed was significantly higher than that of the peel. A total of 125 metabolites were identified by metabolomics, and the types of metabolites were similar in the peel and seed, the dominant ones being terpenoids. However, there was a significant difference in the content of terpenoids between the peel and seed, and the content of oxygenated diterpene metabolites in the peel was significantly higher than that in the seed. Hierarchical agglomerative clustering (HAC) and principal component analysis (PCA) results showed clear separation between the peel and seed, which became more pronounced with increasing maturity. Orthogonal partial least squares-discriminant analysis (OPLS-DA) identified 124 differentially accumulated metabolites (DAM) between tissues. At 29, 47, and 73 DAB, 91, 94, and 96 DAM were found between the peel and seed, respectively, all of which were dominated by oxygenated monoterpenes, sesquiterpenes, and oxygenated sesquiterpenes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of DAM revealed that the differential pathways were mainly related to stress resistance, which might affect the antibacterial activity. The results of antibacterial tests showed that the peel had significantly higher antibacterial activity against Bacillus subtilis, Listeria monocytogenes, Staphylococcus aureus, and Staphylococcus epidermidis than did the seed. The spectrum-effect relationship analysis identified 30 potential quality markers for the antibacterial activity of the peel, dominated by oxygenated monoterpenes, sesquiterpenes and oxygenated sesquiterpenes. In conclusion, the metabolome and antibacterial activity of the essential oil of A. hainanensis fruits exhibited significant spatiotemporal heterogeneity, highlighting the potential application value of the peel as Chinese herbal medicinal waste and providing a reference for the application of A. hainanensis fruits in the food and medicine industries.