From agricultural waste to light-colored lignin: A DES-H2O2 strategy for sustainable UV-protective cosmetics

The valorization of agricultural waste is critical for sustainable development, yet challenges persist in obtaining light-colored lignin with preserved structural integrity. In this study, an innovative one-step pretreatment strategy integrating deep eutectic solvents (DESs) with H 2 O 2 was developed to extract light-colored lignin directly from tea stem waste. The DES-H 2 O 2 system enabled the selective dissociation of lignin–carbohydrate complexes while preserving the fundamental aromatic structure of lignin. By varying the H 2 O 2 dosage, significant improvements in lignin decolorization were achieved, as evidenced by a marked reduction in the color difference relative to milled wood lignin (MWL). Comprehensive characterization using FTIR, GPC, Zeta potential, 31 P NMR, 2D-HSQC NMR, and XPS revealed that H 2 O 2 -induced oxidation not only facilitated the conversion of non-conjugated carbonyls into conjugated structures but also induced molecular depolymerization, reduced particle size and hydrogen-bond, and enhanced surface electronegativity. These modifications contributed to decreased chromophore efficiency and suppressed aggregation, ultimately yielding lignin with improved optical properties. Furthermore, incorporation of the light-colored lignin into a commercially available base cream demonstrated its potential as a sustainable UV-shielding agent, achieving a sun protection factor (SPF) exceeding 50 at optimal lignin concentrations. This work provides a promising green pathway for the high-value utilization of agricultural waste and lays the groundwork for the development of environmentally friendly, high-performance natural UV-protection products.