Comparative Analysis of Phytochemical Profile, <i>In Vitro</i> Bioaccessibility, Cytotoxicity, and Life Cycle Analysis of Polyphenols Extracted from Tea Factory Waste Using Conventional, Microwave, and Ultrasound Techniques

The sustainable valorization of tea factory waste offers a low-cost source of bioactive compounds, particularly polyphenols. This study comparatively evaluated conventional solvent extraction (CSE), microwave-assisted extraction (MAE), and ultrasound-assisted extraction (UAE) for polyphenol recovery. Extraction conditions were optimized, and the resulting extracts were characterized by LC-MS/MS, assessed for in vitro bioaccessibility and cytotoxicity, and evaluated through life cycle assessment (LCA). MAE yielded the highest total polyphenol content (7539.43 ± 85.46 mg GAE/L), outperforming CSE (6530.83 ± 59.25 mg GAE/L) and UAE (4719.52 ± 89.08 mg GAE/L). LC-MS/MS revealed that MAE extracts contained elevated levels of gallated catechins and glycosylated flavonoids. In vitro digestion, however, reduced polyphenol retention, particularly in MAE samples. Elemental analysis confirmed safe levels of essential microelements, supporting their nutraceutical relevance. Importantly, LCA results demonstrated that MAE minimized environmental burdens compared to CSE and UAE. Overall, MAE emerges as an efficient, rapid, and ecofriendly approach for industrial-scale valorization of tea waste into nutraceuticals and functional food applications.