Headspace purging was performed
with ultrapure nitrogen for 10 min at 10 mL/min and
40 8C and the volatiles were adsorbed onto a trap in a model
CDS 6000 purge and trap concentrator (CDS Inc., Oxford,
Pa., U.S.A.). Volatiles were desorbed from the trap by heating
to 275 0C for 10 min and thermally injected into a gas chromatograph
(Dani) equipped with a Stabilwax capillary column
(30 m, 0.32 mm i.d.; Restek). The column temperature
was programmed from 40 0C to 200 8C at 3 8C/min, the flame
ionization detector temperature was 250 8C., with nitrogen
carrier gas at a flow rate of 1 mL/min. Calibration was performed
up to 10 ppm for each constituent by dosed addition
in sterile standard cow milk and soymilk.