Deep eutectic solvent-mediated demethylation of citrus polymethoxyflavones: Effects, optimization, and bioactivity evaluation

Deep eutectic solvent (DES)-mediated demethylation presents a novel strategy for valorizing agricultural waste. This study investigated the demethylation of polymethoxyflavones (PMFs) from citrus peel with DES and its effects on final products’ biological activity. Six DESs with different functional groups ( carboxylic acid, alcohol and amide) were compared for PMF demethylation efficiency. Results showed that acidic DES effectively promoted PMF demethylation to form 5-hydroxy-polymethoxyflavones (5-OH-PMFs), with pH, hydrogen bond strength, polarity and reaction temperature being key factors. Under optimized conditions (1:5 g/L solid-liquid ratio, 480 W microwave power, 10 min), choline chloride/citric acid achieved 96.32 ± 0.06 % demethylation efficiency. Moreover, the system retained a conversion efficiency above 75 % after four consecutive cycles. Bioactivity evaluation further revealed that 5-OH-PMFs exhibited significantly enhanced antioxidant and anti-inflammatory effects compared to PMFs in RAW264.7 cells, due to increased antioxidant enzyme activity and elevated expression of anti-inflammatory factors. Simulated gastrointestinal digestion further improved 5-OH-PMF bioavailability. In summary, this study demonstrated the effectiveness of using DES to catalyze PMFs demethylation as a promising and sustainable method to enhance their bioactivity. It provides a new perspective for preparing demethylated bioactive compounds from citrus and other plant resources. • Acidic deep eutectic solvents catalyze citrus polymethoxyflavones demethylation to 5-hydroxy-polymethoxyflavones. • Demethylation efficiency is affected by DES pH, hydrogen bond strength, polarity, and temperature. • Choline chloride/citric acid achieved a polymethoxyflavones demethylation rate of 96.32 %. • 5-hydroxy-polymethoxyflavones show stronger antioxidant and anti-inflammatory activities than polymethoxyflavones.