Volatile reduced sulphur compounds in butter by solid phase microextraction

The reduced sulphur volatiles, methanethiol and dimethyldisulphide (but not dimethylsulphide), have been detected in the headspace of butter samples. Their concentrations in the butter itself were calculated by determination of the distribution coefficient (K) through spiking butter samples with known quantities of methanethiol and dimethyldisulphide. The K values obtained suggest that the dimethyldisulphide had a greater affinity than methanethiol for the lipid phase of the butter. Solid phase microextraction used in conjunction with gas chromatography -mass spectrometry has been shown to be an effective method for headspace analysis and was used for quantifying the butter headspace concentrations of the reduced sulphur compounds. Seasonal variation of both methanethiol and dimethyldisulphide were found in a series of butter samples. the highest concentration being in spring with an overall decrease through the New Zealand summer. Grass type and condition appeared to influence the concentrations of these compounds in the butter. Storage of the series of butter samples at 4 degrees C for 5 weeks resulted in a significant decrease in the concentrations of both methanethiol and dimethyldisulphide. The dimethylsulphide concentration in all butter samples was below the detection limit of the analytical system used.