Preparation and quality variation of crude fish oil from Leiocassis longirostris via salting-fermentation

To enhance the value-added utilization of Leiocassis longirostris by-products, this study used the visceral fat of L. longirostris as the raw material and adopted the salting-fermentation method to prepare crude L. longirostris fish oil, with the conventional steaming method as the control. We investigated the effects of different salinities and salting-fermentation durations on the quality of the resulting crude fish oil. The results indicate that the optimal quality of crude L. longirostris fish oil was achieved at 35 ℃ with a salting-fermentation duration of 3 d and a salinity of 10%. Under these conditions, the oil yield was (83.20±2.19)%, the extraction rate was (95.37±2.51)%, the acid value was (3.50±0.08) mg·g⁻¹, the peroxide value was (12.44±0.06) meq·kg⁻¹, the iodine value was (141±0.43) g·100 g⁻¹, and the relative content of moisture and volatile substances was (0.24±0.02)%. Furthermore, the crude fish oil prepared under these conditions exhibited the highest relative content of polyunsaturated fatty acids (PUFA), reaching (53.89±2.09)%, among which the combined relative content of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) was (8.33±1.68)%. The correlation network analysis reveals that palmitic acid content could effectively characterize the deterioration degree of crude L. longirostris fish oil, while DHA content was the most critical fatty acid for characterizing the quality of the crude fish oil. Compared with the conventional steaming method, the crude fish oil prepared by the salting-fermentation method has superior quality, better color and higher PUFA content, which provides technical support for the high-value utilization of L. longirostris processing by-products.