Comparative Evaluation of Undaria pinnatifida Anatomical Parts for Skin-Related Functional Properties in UVB-Irradiated L929 Fibroblasts Under Normal and High-Glucose Culture Conditions

Sea mustard (Undaria pinnatifida, UP) is widely cultivated for food in many countries, including South Korea, but several anatomical parts, including the sporophyll, root, and stem, remain underutilized and represent potential resources for value-added utilization. This study comparatively evaluated the in vitro biological activities of extracts from the UP leaf and underutilized anatomical parts, with particular emphasis on skin-related functional properties in UVB-irradiated L929 fibroblasts cultured under normal- and high-glucose conditions. Inhibitory activities against skin-related enzymes were assessed using tyrosinase, hyaluronidase, elastase, and collagenase assays, together with α-glucosidase and xanthine oxidase inhibition. The root extract exhibited the strongest enzyme inhibitory activities, including tyrosinase (35.58%), hyaluronidase (64.58%), elastase (10.05%), and collagenase (98.04%), and showed the lowest IC50 values for α-glucosidase (0.22 mg/mL) and xanthine oxidase (0.65 μg/mL). At 50 μg/mL, all extracts maintained relative MTS metabolic activity above that of the untreated control, while live/dead staining indicated low percentages of dead cells (9.75–15.89%). UP extracts reduced intracellular ROS under the tested oxidative-stress conditions, with the root extract generally showing the greatest reduction, and promoted in vitro scratch closure relative to untreated cells. These findings demonstrate the in vitro functional potential of different U. pinnatifida anatomical parts, particularly the underutilized root, and support their further investigation as value-added functional ingredients.