Page 268 - Analytical method for food addtives

178 Analytical methods for food additives

10
GC–FID method (free adipic acid )
Aqueous extraction
500 mg of the acetylated adipic cross-linked starch sample was weighed accu-
rately (1.0 mg) in a glass reaction tube, and 4.0 mL distilled water and 1.0 mL
aqueous solution containing 0.05 mg pimelic acid/mL were added. The reaction
tube was closed and the adipic acid was extracted by continually rotating the tube
for 16 h. The aqueous suspensions were centrifuged for 10 min at 2900 g. The
starch-free aqueous solution was transferred to a clean reaction tube. 100 µL of
6 M HCl and 5 mL ethyl acetate were added, the tube was closed and shaken
vigorously for 1 min to extract the adipic acid and pimelic acid into the ethyl
acetate. Then as for total adipate (see p. 177) from*.

Methanol–acetic acid extraction
500 mg of the acetylated adipic cross-linked starch sample was weighed accurately
(1.0 mg) in a glass reaction tube, and 4.0 mL methanol, 1.0 mL aqueous solution
containing 0.05 mg pimelic acid/mL and 100 µL acetic acid were added. The
reaction tube was closed and the adipic acid was extracted by continually rotating
the tube for 16 h. The aqueous suspensions were centrifuged for 10 min at 2900 g.
The starch-free supernatant was transferred to a clean reaction tube and evaporated
to dryness with a stream of nitrogen in a Pierce Reacti-Vap evaporator at a
temperature of 30 ºC in a water bath.

Silylation
As for total adipate (see p. 177).
GC conditions
As for total adipate (see p. 177).

Calibration
Four 50 mg (total adipate) or five 500 mg (free adipic acid) samples of waxy corn
starch were weighed into reaction tubes. 1.0 mL aqueous or methanolic pimelic
acid containing 0.05 mg pimelic acid/mL was added into each tube followed by the
addition of 0.00, 0.25, 0.50, 0.75 and 1.00 mL aqueous adipic acid solution,
containing 0.05 mg adipic acid/mL into the respective tubes. The volume was
adjusted to 2.50 mL (total adipate) with distilled water and the procedure as
described in the sample preparation section was carried out on 5.0 mL (free adipic
acid) with the extraction solvent, and the extraction procedure was carried out as
described above.