Recovery and characterization of sardine oil extracted by pH adjustment

A new oil extraction method involving pH adjustment was developed and compared with the traditional heat extraction method. Sardine oil was obtained by adjusting the pH to the isoelectric point (pI) of sardine muscle (pH 5.5) using HCl or food-grade organic acids [with/without calcium (Ca)] followed by centrifugation. Oil extracted with citric acid plus Ca showed the best quality, along with good recovery, the lowest haze value, and the highest n-3 polyunsaturated fatty acid content. All oils extracted by pH adjustment exhibited high stability against oxidation supported by low conjugated dienes and thiobarbituric acid reactive substance level with fewer impurities compared to the heat process. There was a significant beneficial effect of Ca addition prior to pH adjustment in terms of lipid oxidation stability and color of the final products. The pH adjustment method is a novel process for oil extraction and a promising method that can be utilized for high-oil pelagic species such as Pacific sardines.