Objective Tea bran, also referred to as tea residue or tea seed cake, is the residual by-product generated after the extraction and pressing of tea oil. As a traditional agricultural waste product, the high-value utilization of tea bran plays a significant role in promoting the development of a green circular economy. Therefore, determining its chemical composition and biological activity is fundamental to realizing such high-value applications. Methods This study aimed to optimize the extraction process of tea bran extract and to quantitatively determine its tea saponin (TS) and total flavonoid (TF) contents using ultraviolet-visible (UV) spectrophotometry. The phytochemical composition of the extract was systematically characterized via ultra-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (UPLC-Q-TOF-MS/MS). Furthermore, its in vitro biological activities were evaluated, including antibacterial effects against Staphylococcus aureus ( S. aureus ) and methicillin-resistant Staphylococcus aureus (MRSA) by determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using the broth dilution method, as well as antioxidant potential via DPPH and ABTS radical scavenging assays. Results This study established an optimal method for extracting tea bran extract using reflux extraction with 80% ethanol-water as the solvent, involving two extraction cycles of 90 min each. UV spectroscopic analysis revealed that tea saponins were the predominant constituents of the extract, with a content of (130.44 ± 0.54) mg/g, whereas the total flavonoid content was only (50.75 ± 2.21) mg/g. A total of 51 compounds were preliminarily identified in the extract using UPLC-Q-TOF-MS/MS. Furthermore, in vitro bioactivity assays demonstrated that the tea bran extract exhibited significant antibacterial activity against Gram-positive bacteria, including S. aureus and MRSA. The extract also exhibited notable antioxidant activity, with half-maximal inhibitory concentration (IC 50 ) values of (131.94 ± 7.79) μg/mL for the DPPH radical and (299.21 ± 3.64) μg/mL for the ABTS radical. Conclusion As the primary constituent of tea bran extract, tea saponin is a naturally occurring antimicrobial agent that also exhibits antioxidant properties. The present study provides fundamental guidance for the comprehensive development and utilization of tea bran.
Tan et al. (Mon,) studied this question.