Efficient Extraction of Tea Polyphenols and Their Bioactive Preservation Using Magnetic-Induced Electric Field

Tea polyphenols (TPs) are valuable bioactive compounds derived from tea with diverse health-promoting effects. However, efficient extraction of TP with preserved bioactivity remains a challenge. This study evaluated magnetic-induced electric field (MIEF) technology for efficient TP extraction. Under optimized conditions (solid-liquid ratio 1:30, conductivity 1000 μS/cm, voltage 800 V, frequency 70 kHz, 60 min, and 30 °C), MIEF achieved a TP yield of 223 mg/g, exceeding those of water bath extraction (WE, 194.05 mg/g) and ultrasound-assisted extraction (UE, 201.97 mg/g) by 14.91% and 10.41%, respectively. Catechin composition and other fundamental chemical components were also enhanced, with notably higher dissolution of ester-type catechins (epigallocatechin gallate and epicatechin gallate) by 21.2% and 10.4% over WE. MIEF treatment induced a honeycomb-like porous structure (20–80 nm) in tea residues with a 7.1-fold increase in specific surface areas (3.24 m2/g) relative to untreated control. MIEF extract solutions contained uniformly dispersed nanoparticles (140–160 nm) with a higher negative charge (ζMIEF-30 ≈ –60 mV), compared with WE (ζWE ≈ –20 mV) and UE (ζUE ≈ –40 mV). Moreover, MIEF extracts exhibited brighter yellow hues than the dull reddish tones observed for WE and UE extracts, suggesting reduced TP oxidation and polymerization during low-temperature MIEF extraction. The lowest IC50 values for antioxidant activity (determined by DPPH, ABTS, and FRAP) and digestive enzyme inhibition (α-amylase, α-glucosidase, and pancreatic lipase) were obtained for MIEF extracts, indicating better preservation of TP bioactivity. By simultaneously achieving efficient extraction and bioactivity preservation, MIEF represents a promising strategy for the valorization of plant-derived bioactive compounds.