Differences in Chemical Profiles, Phenolic Content, and Antioxidant Activity of Prunella vulgaris L. at Different Ripeness Stages

<i>Prunella vulgaris</i> L. (PV) is a versatile plant with medicinal and culinary applications globally. Its mature fruit-spikes (red-brown) are the primary source of traditional medicine and herbal tea. However, large-scale cultivation and harvesting inevitably leads to the unintended inclusion of immature green fruit-spikes, which are considered substandard medicinal parts. To explore the medicinal and nutraceutical potential of green fruit-spikes, our study systematically compared green and red-brown samples. The distinctions between the two fruit-spikes were characterized by determination of total water-soluble extract content, comprehensive chemical difference analysis, and quantitation of six phenolic acids, including Danshensu, caffeic acid, protocatechuic acid, protocatechualdehyde, salviaflaside, and rosmarinic acid. Additionally, variations in antioxidant activity were evaluated by DPPH and ABTS assays. As a result, 106 compounds were identified from the PV samples. Green spikes exhibited higher total water extract yield and contents of the six phenolic acids than the red-brown ones. Moreover, green samples showed greater accumulations of phenolic acids, flavonoids, and triterpenes. Concomitantly, stronger antioxidant activity was displayed in green spikes in both assay models. Caffeic acid, danshensu, rosmarinic acid, and protocatechualdehyde were identified as major contributors by Pearson correlation analysis. Our findings reveal that green fruit-spikes possess advantages in accumulating specific chemical profiles and exhibiting antioxidant activity, highlighting their untapped pharmaceutical and nutraceutical potential.