The aim of this study was the quantitive determination of cis-9, trans-11 isomer by two methods: gas chromatography (GC) and silver-ion high performance liquid chromatography (Ag+HPLC) in ewes milk fat. The study was carried out on 20 ewes of Wrzosówka and Żelazneńska sheep, which were mantained at the same environmental and nutritional conditions. The milk samples have been collected from ewes at the age of 3—1 years and in the 4th week of lactation. The chemical composition, as well as fat content, was similar in both studied breeds. The amount of C18 fatty acids connected with the major CLA isomer did not show statistical differences between breeds, besides of C18:3, which was higher (P < 0.03) for Wrzosówka. The activity of A9 desaturase, the enzyme responsible for endogenous synthesis, was also higher (P < 0.01) for Wrzosówka ewes. The content of cis-9, trans-11 C18:2 isomer in milk fat of studied ewes determinated by GC method did not differ with this obtained by Ag+HPLC. The difference has not been noted also within studied breeds. Obtained results suggest, that major CLA isomer in milk could be sensitively identified what allow to precisely determining its amount both by classic GC method and Ag+HPLC method.
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