Optimization of Non-Enzymatic Ultrasound-Assisted Extraction of Yellowfin Tuna Head Oil and Comparison with Enzyme-Assisted Extraction Oils

Yellowfin tuna heads (YFTH), a major by-product of tuna processing, are rich in lipids and long-chain n-3 polyunsaturated fatty acids. This study developed and optimized an ultrasound-assisted extraction process without exogenous protease addition, termed non-enzymatic ultrasound-assisted extraction (NE-UAE), for recovering yellowfin tuna head oil (YFTO). The term NE-UAE distinguishes this process from the enzyme-assisted comparators and does not denote a different ultrasonic mechanism. A four-factor, three-level Box–Behnken design was used to optimize nominal ultrasonic power, heat-treatment temperature, liquid-to-solid ratio, and ultrasonic treatment time. The predicted local-optimum conditions were 58.3% of the 1000 W rated power (nominal setting, 583 W), 64.0 °C, 3.0 mL/g, and 31 min, respectively, yielding a validated oil recovery of 63.92 ± 0.24%. The NE-UAE oil (NETO) was compared at the process-chain level with oils obtained by papain-, trypsin-, and Alcalase-assisted aqueous extraction. Under the tested conditions, NETO had lower acid value, initial peroxide value, and p-anisidine value, a lighter color, and lower relative abundances of putative oxidation-related electronic-nose marker signals. Polyunsaturated fatty acids comprised 38.39% of total fatty acids in NETO, including 7.43% EPA and 27.13% DHA. During accelerated storage at 60 °C for 14 d, NETO showed lower absolute peroxide values and smaller baseline-corrected increases than the comparator oils. Overall, NE-UAE provided a feasible process option for recovering YFTO with acceptable oil recovery and favorable quality-related characteristics under the specific process conditions and comparator process chains examined in this study.