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°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.