Rapid determination of total lipids in fish samples employing extraction/partitioning with acetone/ethyl acetate solvent mixture and gravimetric quantification

Abstract

A simple, non-laborious, fast, cheap, robust and environment friendly method for lipid determination in fish samples was developed. An amount of 5 g of fish tissue homogenate in a centrifuge tube was extracted with 5 mL of acetone/ethyl acetate mixture (6:4, v/v) using vigorous shaking and after addition of inorganic salts (2 g MgSO4 and 0.5 g NaCl) and agitation the organic phase was separated by centrifugation. An aliquot of the organic phase was air-dried and then oven-dried and the lipid content of the fish homogenate was determined gravimetrically on a wet weight basis. The performance of the proposed method was compared with a well-established method according to Smedes (1999) by analysing 66 fish samples with a wide range of lipid content (pollock, chub and salmon). In comparison with the method developed by Smedes, similar repeatability and good agreement between the results from both methods for all analysed samples was achieved. The linearity of the proposed method with a correlation coefficient of 0.9997 was obtained between 0.25 and 15% and limits of detection (LOD) and quantification (LOQ) were 0.11% and 0.34% of total lipids in fish homogenate, respectively. The accuracy of the method was verified by the analysis of NIST standard reference material SRM 1946 (Lake Superior Fish Tissue) and the obtained recovery (at 10.17% of extractable fat) was 99.3% with a relative standard deviation (RSD) of 0.5% (n = 3).