Ultrasound- and Microwave-Assisted Extractions Facilitate Oil Recovery from Gilthead Seabream (Sparus aurata) By-Products and Enhance Fish Oil Quality Parameters

This research aimed to analyze ultrasound (UAE) and microwave-assisted extraction (MAE) as novel technologies for utilizing gilthead seabream (Sparus aurata) by-products to produce high-quality fish oil for human consumption. The impacts of extraction parameters, namely, temperature, time, solvent-to-solid ratio, and their interactions on the extraction yield, are investigated using response surface methodology (RSM), and a central composite rotatable design. The optimized conditions are 15.47 mL g⁻¹ of solvent-to-solid ratio, 38 min, and 42 °C for UAE and 15.84 mL g⁻¹ of solvent-to-solid ratio, 18 min, and 40 °C for MAE. Under optimal conditions, the maximum extraction yields are 38.40 and 36.70% (g/g) for UAE and MAE, respectively. Both UAE and MAE have significantly higher mass transfer rates (61.70 and 121.58 g h⁻¹, respectively) than Soxhlet extraction (10.78 g h⁻¹). The fatty acid composition, physicochemical, and oxidation analyses of fish oils confirm the suitability of both UAE and MAE for the recovery of high-quality oils from fish processing by-products. The valorized oils mainly include unsaturated fatty acids (≈75%) and are rich in oleic acid. Furthermore, scanning electron microscopy analysis reveals that the key driving force for fast oil extraction is the structural degradation of fish by-products caused by ultrasound and microwave. Practical Applications: Due to environmental and economic viewpoints, the validation of fish oil from fish industry by-products has become a popular research topic recently. Alternative recovery techniques such as ultrasound- (UAE) and microwave-assisted extraction (MAE) protocols may have additional benefits in producing functional oils. Interactive effects of process parameters determine the success of the extraction technique; therefore optimization is a critical approach when applying the extraction protocols. This study shows that UAE and MAE techniques significantly enhanced oil extraction rate from gilthead seabream (Sparus aurota) by-products at lower temperatures and by using lower amounts of solvent. UVA and MAE increase oxidative stability and do not change the fatty acid composition. Hence, the by-product of the gilthead seabream can be a sustainable and food-grade fish oil source and UAE and MAE can be a good alternative to the conventional (Soxhlet) extraction by providing high yield and quality oil.