The influence of different sample preparation procedures on the determination of fatty acid profiles of beef subcutaneous fat, liver and muscle by gas chromatography.

Three sample preparation procedures for producing a solution of fatty acid methyl esters (FAME) from the liver, subcutaneous fat and muscle of 9 bulls were compared. Fat was extracted from fresh samples using solvents under ambient (Folch) or high temperature and pressure (ASE) conditions. As an alternative to Folch, a one-step procedure carried out on freeze-dried samples (Jenkins) was used to produce FAME solutions. All methods involved mild acid-base transmethylation and in each case 9 samples of each tissue type were analyzed in duplicate, resulting in the quantification of 77 FAs. Equal amounts of total FAs were extracted with the different methods. The effect of the method on the FA profile was low in fat, intermediate in liver, and high in muscle. Compared with Folch, ASE resulted in higher saturated and monounsaturated FAs and fewer polyunsaturated FAs (PUFAs), and a lower relative incidence of conjugated linoleic acids (CLA) in muscle (>25%) and liver (17%). Jenkins had a smaller influence than Folch on PUFAs, and caused only a weak reduction in CLA (<3.4%). ASE tended to cause greater oxidation of PUFAs and unacceptable alterations to CLAs compared with Folch. The Jenkins procedure is a valid alternative to Folch when freeze-drying of samples is appropriate. [ABSTRACT FROM AUTHOR]