Subcritical water extraction and fractionation: A green approach to recovering antioxidants and caffeine from black tea

Tea ( Camellia sinensis ) is the second most consumed beverage after water, valued for its health benefits (antioxidants) and stimulating properties (caffeine) [ 1 ]. Black tea, a fermented variant, is widely available, including in dietary supplements and other products, but its manufacturing often relies on inefficient and environmentally harmful extraction methods [ 2 ] [ 3 ]. Subcritical water extraction (SWE) is a promising green alternative, enhancing yields and efficiency [ 4 ]. However, globally inconsistent methodologies lead to varying scientific assessments. This study optimized SWE to maximize biologically active compounds, using fractionated extraction (5 x 2 min, 2 x 5 min, 10 min). Furthermore, SWE extracts were compared with traditional tea preparation, water infusion (WI). Results showed that antioxidant activity and caffeine content increased with longer extraction times, particularly in the second 5 min or at 10 min fractions. The strongest antioxidant potential (DPPH IC 50 16.23 μg/mL; ORAC IC 50 6.43 μg/mL; TPC 650.55 mg GAE/g) and highest caffeine content (14.834 μg/mL) were found in the second 5 min fraction. Individual phenolic compounds were determined by LC-MS/MS. Our results also revealed that certain phenolics, such as chlorogenic acid, epicatechin, hyperoside, isoquercitrin, and rutin, require precise extraction timing to optimize yield, as the highest concentration occurred either within the first 5 min or in some of 2 min fractions. However, other compounds, such as catechin or gallocatechin, showed highest concentrations in WI. These findings demonstrate that extraction time significantly affects final extract composition. Furthermore, as different compounds respond to different SWE conditions, further optimization of temperature and pressure is required to improve extraction efficiency. Funding . IGA 20243109. Publication History Article published online: 05 March 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany