Hydrogen extraction as a sustainable method for the recovery of phenolic compounds from tea wastes

The significant production of tea waste globally raises environmental concerns. Tea waste can be valorized by extracting its phytochemicals. In this study, the recovery of phenolic substances, flavonoids, and antioxidants from the black tea wastes using two types of hydrogen-rich water (HRW): hydrogen bubbling and magnesium-water reaction (Mg water), besides ethanol/water (50/50, % vol), ethanol/Mg water (50/50, % vol), and pure water (control) was investigated. The best extraction yield was obtained for HRW (30.13%). The best levels of phenolics (TPC), flavonoids (TFC), and antioxidants (DPPH and ABTS) were found for HRW extracts, followed by ethanol/Mg water (50/50). The levels of TPC, TFC, DPPH, and ABTS increased by 193.05, 210.56, 49.21, and 86.60%, and by 59.70, 33.46, 28.66, and 58.25% when HRW and Mg water was used as a solvent instead of pure water, respectively, in the extraction. The maximum levels of phenolic acids (p-coumaric acid, chlorogenic acid, gallic acid) and flavonoids (rutin and epicatechin) were found in HRW extracts. Hydrogen extraction can be proposed as a sustainable method to extract phenolic substances from agri-food waste.