Metabolic and protein profiles reveal the regulatory mechanisms of selenium biotransformation and bioactive compounds formation in microwave-dried selenium-enriched black tea

• Microwave fields regulated differential metabolites and energy-responsive enzymes • 420 W microwave power promoted the conversion of selenium amino acids in black tea • 420 W microwave drying favored the accumulation of amino acids and flavonoids • Microwave drying of black tea improved the retention of bioactive compounds • Drying quality of selenium-enriched black tea depended on the microwave power level Drying is the key step in the processing of tea, and the heat transfer directly influences the retention of organic fractions such as selenocysteine. Selenium-enriched black tea is a specialized fermented tea with higher organic selenium concentration than conventional black tea. To investigate the biotransformation mechanism of seleno-amino acids and bioactive compound variations during the drying process of selenium-enriched black tea, this study innovatively constructed a microwave power-regulated tea drying system. A multi-gradient microwave power (140, 280, 420, 560, 700 W) combined with metabolomics and proteomics was used to systematically analyze the effects of microwave regulation on black tea. The results demonstrated that the biosynthesis efficiency of selenohomolanthionine stabilized, and the synergistic optimization of flavonoids and amino acids was achieved at the 420 W power setting when the leaf water content reached 3%. The levels of key metabolites, such as myricetin (37.58 mg/kg), epicatechin (32.44 mg/kg), and tryptophan (114.62 mg/kg), peaked at 420 W, with the highest level being 6.66 times higher than the hot-air drying group. The interaction pathway revealed core regulatory enzymes showing energy dependence, including flavonol synthase and phenylalanine ammonia-lyase. This research elucidated for the first time that microwave drying regulates the formation of bioactive compounds in black tea through a dual mechanism of modulating the selenium metabolic pathway and activating flavonoid synthesis and amino acid conversion. These mechanistic insights enable controlled microwave processing, paving the way for the future precise manufacturing of functional selenium-enriched tea.