Functional Evaluation of Sweet Potato Processing Residues for Antioxidant- and Skin-Related Activities in Human Dermal Fibroblasts

Sweet potato (Ipomoea batatas L.) is cultivated globally and generates a large quantity of plant-derived residues, including leaves, stems, and non-commercial cull roots, which remain insufficiently utilized despite their potential functional value. Although the antioxidant properties of sweet potato leaves have been reported, comparative investigations of different plant parts evaluated under the same experimental conditions, particularly in relation to skin-associated biological functions, are still limited. In this study, aqueous extracts prepared from sweet potato leaves, stems, and cull roots were obtained using a food-grade extraction process suitable for practical application. The phenolic composition and biological properties of the extracts were comparatively analyzed. Antioxidant capacity was examined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay, ferric reducing antioxidant power (FRAP), as well as assays associated with superoxide dismutase (SOD)-like and catalase-related activities. Skin-related biological responses were further evaluated by measuring elastase and collagenase inhibition, type I procollagen synthesis, and matrix metalloproteinase-1 (MMP-1) secretion in CCD-986Sk human dermal fibroblasts. Among the tested samples, the leaf-derived aqueous extract exhibited a higher total phenolic content, greater accumulation of chlorogenic acid, and stronger antioxidant responses compared with stem and cull root extracts. In addition, the leaf extract showed more pronounced effects on collagen metabolism, including enhanced procollagen synthesis and reduced MMP-1 secretion, while maintaining acceptable cell viability within the tested concentration range. Overall, these results demonstrate clear tissue-dependent functional differences among sweet potato residues and indicate that leaf-derived extracts represent a promising functional material for skin-related and cosmetic applications.