Valorization of Kinmen Peanut Skin, an Agro-Industrial By-Product: A Polyphenol- and Phytosterol-Rich Extract with Antioxidant and Hypolipidemic Effects in Hamsters

Kinmen peanut (Arachis hypogaea L. cultivar Kinmen No. 1) is a unique crop used to produce local specialty “peanut candy”; however, the peanut skins (PSs) are treated as waste owing to the bitter taste. To support the valorization of this agro-industrial by-product, peanut skin ethanolic extract (PSE) was prepared and evaluated for its hypolipidemic potential in a cholesterol/fat-fed hamster model, together with its antioxidant capacity and chemical composition. Hamsters were fed a cholesterol/fat-enriched diet supplemented with PSE at 0.1%, 0.2%, or 0.4% (w/w) for 8 weeks. Serum lipid profiles were determined, and derived atherogenic indices were calculated. In parallel, antioxidant activity was assessed using 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and reducing power assays, while chemical characterization included total phenolics, crude phytosterols, and HPLC profiling of representative phenolic compounds. PSE significantly reduced serum total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) compared with the cholesterol/fat-enriched control, whereas triglycerides were not significantly altered. The LDL-C/HDL-C ratio was also reduced in PSE-treated groups, with the greatest reduction observed in the 0.1% PSE group (0.33 ± 0.04 vs. 0.56 ± 0.12 in the negative control). In addition, PSE exhibited marked antioxidant activity, with IC50 values of 141.3 and 76.2 μg/mL in the DPPH and ABTS assays, respectively. Chemical analyses showed that PS contained 1098 ± 189 µg β-sitosterol equivalents/g PS and 199.3 ± 4.6 mg gallic acid equivalent (GAE)/g PS, and HPLC identified p-coumaric acid, ferulic acid, gallic acid, chlorogenic acid, daidzein, catechin, and resveratrol as representative phenolic constituents. Collectively, these findings support Kinmen peanut skin as a promising value-added source of bioactives for functional ingredient development targeting cholesterol dysregulation and oxidative processes.