Fish oils are becoming a promising component as human food and a widely used industrial material. Although the raw materials are readily available, fish oil extraction becomes difficult due to lack of proper knowledge. The present study was carried out to evaluate the efficiency of the four different methods, i.e.formic acid silage, microbial silage, steaming and wet rendering methods, compared with that of standard Bligh & Dyer method. The yield in each method was measured and the quality of the extracted oil was determined by measuring peroxide value(PV), free fatty acid value(FFA) Iodine value(IV) and fatty acid composition(FAC)
The yield of oil was significantly higher(8.5% oil, p < 0.05) in the acid silage method compared with the standard Bligh & Dyer Method(11.55%) used in this study. In addition, steaming method gave an intermediate value (6.03%) within a short period of time. Yields obtained from the microbial silage method, 2.2% and the wet rendering method(2.95%) were very low. The quality of oil extracted by the acid silage method, measured by peroxide value (66.8 ±4.8 m.eq/kg, p<0.05) and free fatty acid values (5.75± 0.3%, p<0.05), were higher than the oils from other methods. The extracted oil from the steaming method showed a significantly lower PV (13.0 ± 0.7 m.eq/kg ,p<0.05), FFA value (3.86± 0.2%, p<0.05) and higher iodne value (126.6 4.1g of I absorbed/100g,p<0.05). The percentage of saturated and monounsaturated fatty acids increased whereas the polyunsaturated fatty acids decreased during all extrations, and these changes were minimum in steaming extraction than the other methods. Based on the cost yields and oil quality, the acid silage method and the steaming method were found to be more suitable for fish oil production as a commercial basis than the other two methods used in the study.