Skatole and indole concentrations in Longissimus dorsi and fat samples of pigs

A HPLC-NP (normal phase-high performance liquid chromatography) method for determining the concentration of skatole and indole in Longissimus dorsi samples is described. Lipids containing skatole and indole were extracted in chloroform:methanol (2:1) at room temperature and dehydrated by liquid-liquid extraction with an aqueous solution saturated with 10% of sodium chloride. The organic phase was evaporated to dryness and redissolved in 10 ml of hexane:2-propanol (92:8). Indolic compounds were separated on a Hypersil aminopropylsilica column (5 μm) (250×4.6 mm i.d.). The mobile phase was hexane:2-propanol (92:8) and detection was by fluorescence (excitation at 280 nm and emission at 360 nm). Linearity was found in the range of 0.05-0.4 μg/g and the coefficient of correlation was above 0.99 for both compounds. The within day (n=5) variation was at 0.05, 0.2 and 0.4 μg/g and the CV (coefficient of variation) values for relative areas determined at these concentrations were less than 13%. This method was used to compare the concentrations of skatole and indole in different samples: L. dorsi muscle, the fat covering the L. dorsi and subcutaneous fat. A correlation was observed between the concentration of indole and skatole in the back fat and fat covering the L. dorsi samples (P<0.001, r=0.99). No significant correlation was obtained in L. dorsi samples, between skatole and indole levels. In spite of the correlation shown between skatole and indole concentrations in the back fat and L. dorsi samples, the mean concentrations of these compounds were significantly higher (P<0.05) in the back fat samples.