Phytochemical profiling and antioxidant activity of ethanolic extracts from thinned immature 'Shiranuhi' mandarin peels and their effects on rapeseed oil stability.

Phenolic composition and antioxidant activity of ethanol extracts from peels of 'Shiranuhi' mandarin at seven maturity stages were analyzed. Non-targeted UHPLC-MS/MS identified 1492 compounds, with phenolics accounting for 75.90 %-86.62 % of metabolites. Antioxidant capacity increased with fruit maturity, peaking at YF2, and then declined. Flavonoids were the dominant phenolic compounds, and lipophilic flavonoids such as hesperetin, naringenin, and demethylnobiletin showed strong correlations with oxidative stability (R > 0.50, p < 0.05). At 28 days of accelerated storage, TOTOX inhibition by YF2 extract reached 18.79 %, indicating high oxidative suppression. Lipophilic flavonoids played a key role in enhancing oil stability by inhibiting lipid peroxidation. Although TBHQ exhibited stronger protection, natural extracts offered safety advantages. Increasing concentration or purity, or combining with synthetic antioxidants, may optimize their application. Thinned immature citrus peel is rich in antioxidant compounds, highlighting its potential as a natural antioxidant source and a sustainable strategy for by-product utilization.