Cla methyl esters

The composition of fatty acids was determined applying the method of gas chromatography with the help of Hewlett Packard 6890 GC System (Műnster, Germany) with a flame ionization detector (FID) in 100 m capillary column (produced by Chrompack, Middelburg, the Netherlands) with CP Sil 88 phase. The column diameter was 0.25 mm, and the film was 0.20 μm thick. The used separation conditions are presented in Table 2.
Identification of fatty acids was carried out based on the comparison of their retention time with the retention time of methyl esters of fatty acids of reference milk fat (BCR Reference Materials) of CRM 164 symbol. Examples of chromatograms are shown in Figure 1. The positional trans isomers of C18:1 were identified using the standards of methyl esters of these isomers (trans6, Supelco and trans9 and trans11, Sigma-Aldrich, St. Louis, MO, USA), whereas the trans isomers of C18:2 acid (cis,trans and trans,cis) were identified with the use of a mixture of standards of C18:2 isomers (Supelco). The cis9trans11 CLA isomer was identified using a mixture of CLA methyl esters (Sigma-Aldrich). The proportions of the individual acids were calculated by the ratio of their peak area to the total area of all identified acids (% mass fraction).

Methyl esters of fatty acids were identified according to their retention times, after comparison with retention times of methyl esters of the reference milk fat fatty acids (BCR Reference Materials) of the CRM 164 symbol, and literature data [51 (link),52 (link),53 (link),54 (link)]. The cis9trans11 C18:2 (CLA) isomer was identified using a mixture of CLA methyl esters (Sigma-Aldrich, Germany). To calculate the percentage of fatty acids, the proportions of the peak areas of individual acids in relation to the total area of all identified peaks were used.

Identification of fatty acids was carried out based on a comparison of their retention time with the retention time of methyl esters of fatty acids of the reference milk fat (BCR Reference Materials) of the CRM 164 symbol and literature data [76 ,77 (link),78 (link),79 (link)]. The cis9trans11 C18:2 (CLA) isomer was identified using a mixture of CLA methyl esters (Sigma-Aldrich, Germany). The contents of fatty acids were calculated in mg/g fat according to the applicable standard (methyl ester of C21:0 acid, Sigma-Aldrich, Germany). The statistical analysis of results was carried out using Statistica version 13.1 (StatSoft; Cracow, Poland) [74 ] software based on a one-way analysis of variance (ANOVA) at a significance level at P < 0.05. The differences between mean values were evaluated using Duncan’s test.