Volatile compounds were analyzed using dynamic headspace
analysis, as described by Murti and others (1993). After
thawing the 5 mL of frozen sample, 500 mg of ammonium
sulfate was added to accelerate the precipitation of proteins
and release volatile compounds. Lauric acid was added (0.3
mg) as an antifoaming agent. 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.