Fast and sustainable extraction of light-colored lignin using oxalic acid dihydrate: Toward structural elucidation...

Lignin, an abundant and complex biopolymer, offers significant potential for high-value applications in diverse industries due to its antioxidant and UV-absorbing properties. However, its utilization in cosmetic formulations, particularly sunscreens, is impeded by its dark coloration. Herein, this study introduced an innovative approach for extracting light-colored lignin with well-preserved structure from wheat straw using oxalic acid dihydrate (OAD) under mild conditions. The OAD method significantly improved lignin color, accelerated the extraction process (within 5 min), and emphasized environmental sustainability, representing a marked improvement over traditional technique. Lignin isolated by the OAD method achieved yields up to 91.24 %, with an attractive light color and elevated purity. Comprehensive structural analyses revealed a substantial enrichment in phenolic hydroxyl groups and an advantageous S/G ratio, indicating superior antioxidant and UV-blocking efficacy. The antioxidant capacity, evaluated through DPPH radical scavenging assays, was exceptional, with an IC50 value below 0.1 mg/mL. Moreover, the addition of 5 % OAD-extracted lignin to pure cream indicated that SPF (SPF_invitro = 7.52) was higher than P25 (SPF_invitro = 5.92). This study underscores a highly efficient and environmentally benign method for producing premium, light-colored lignin, advancing its application in natural, sustainable cosmetic formulations.