Microwave Effects on Structure and Antioxidant Activity of Perilla Oil Melanoidins

ABSTRACT Melanoidins contribute to the sensory and functional properties of perilla oil. This study explored the impact of microwave pretreatment on the formation, structure, and antioxidant activity of melanoidins in perilla oil. Structural characteristics were analyzed using Fourier‐transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–Vis), fluorescence spectroscopy, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS), and ultra‐high‐performance liquid chromatography coupled with quadrupole time‐of‐flight mass spectrometry (UPLC‐Q‐TOF‐MS). Antioxidant activity was evaluated by DPPH and ABTS radical scavenging and reducing power assays. Results showed that higher microwave intensity promoted the formation of melanoidins, reflected by increased absorbance and fluorescence signals. The strongest DPPH activity (142.35 μmol TE/g) was observed at 700 W for 10 min, while the highest ABTS activity (159.03 μmol TE/g) occurred at 540 W for 8 min. Melanoidins formed under these conditions contain glyoxal‐derived polymeric units and nine free phenolic compounds, including caffeic acid, rosmarinic acid, luteolin, and others. Among them, rosmarinic acid was dominant (18.73–43.02 μg/100 mg), followed by caffeic acid and apigenin. Microwave treatment significantly increased total soluble free phenolics, supporting their synergistic contribution to antioxidant enhancement. The study demonstrates that microwave pretreatment can enhance the structural complexity and functional properties of melanoidins in perilla oil. These findings highlight the potential application of melanoidins as natural antioxidants in functional foods and nutritional products.