Cross-supply-chain by-product valorization: optimization of Sorrento lemon peel aromatization of refined olive and grape seed oils via Ultrasound-Assisted Extraction

The growing challenge of food waste highlights the need for strategies that reintroduce discarded materials into the food chain with added value. Sorrento lemon peels and grape seed oil are by-products of the citrus and wine industries that are often underutilized despite their potential, while the refined olive oils are obtained from low-quality virgin oils. In this study, these three materials were jointly valorized through ultrasound-assisted extraction to produce lemon-flavored oils with improved functional and sensory properties. A Design of Experiments approach was applied, and experimental data were fitted to second-order polynomial models to optimize the aromatization process based on peroxide value. Oil quality was further evaluated through free acidity, UV spectrophotometric indices, total phenolic content (TPC), antioxidant activity (DPPH), and volatile profiling (HS-SPME-GC–MS). Optimal conditions were identified as 3 min, 0.15 g/g matrix-to-oil ratio, 15 °C for olive oil, and 16.5 min, 0.25 g/g, 15 °C for grape seed oil. Under these conditions, the flavored olive oil showed the highest citral percentage and a threefold increase in TPC (from 54.24 ± 8.04 to 179.06±6.87 mg GAE/kg), while the flavored grape seed oil exhibited a fourfold increase compared to controls (from 42.41±8.29 to 168.22±1.10 mg GAE/kg) . Moreover, off-flavors present in the base oils were not detected. This approach provides a sustainable and scalable method to convert multiple low-value by-products into higher-value flavored oils.