Page 125 - Analytical method for food addtives

E220–8: Sulphites 75

solid test portions are injected into LC or anion exclusion chromatographic system
equipped with anion exclusion column and electrochemical detector. 10,11 A summary
of the procedure for this method is given in the Appendix and a summary of the
statistical parameters in Table 8.6.
A flow injection analysis (FIA) method for the analysis of sulphite (total) in
foods and beverages, applicable to the determination of ≥5 µg/g total SO in
2
13
shrimp, potatoes, pineapple and white wine has been collaboratively tested. The
method measures sulphur dioxide by FIA using reaction with malachite green. In
the FIA system, test solution is reacted with NaOH to liberate aldehyde-bound
sulphite. Then, the test stream is acidified to produce SO gas, which diffuses
2
across a Teflon membrane in the gas diffusion cell into a flowing stream of
malachite green, which is discoloured. The degree of discolouration of malachite
green is proportional to the amount of sulphite in test solution. 12,13 A summary of
the procedure for this method is given in the Appendix and a summary of the
statistical parameters is given in Table 8.7.
A flow injection analysis (FIA) method for the analysis of sulphite (free) in
wines, applicable to the determination of free sulphite and bound sulphite that is
15
labile at pH 2.2 has been collaboratively tested. The method measures sulphur
dioxide by FIA using reaction with malachite green. Injected test portion aliquot is
mixed with concentrated citric acid solution (pH about 2), which forms SO gas
2
from free sulphite and from the portion of bound sulphite that is labile under these
conditions. SO gas diffuses across a Teflon membrane in the gas diffusion cell into
2
a flowing stream of malachite green solution. Malachite green is discolourised in
proportion to the amount of SO gas that diffuses across the membrane. The degree
2
of discolouration of malachite green is measured spectrophotometrically. 14,15 A
summary of the procedure for this method is given in the Appendix and a summary
of the statistical parameters is given in Table 8.8.
An extensive survey of sulphite containing foods (211 samples of foods and
27
beverages) has been carried out in Italy. The determination of sulphite was
3
performed on all samples according to AOAC 990.28 with the exception of wine
for which the determination was performed according to EU official method (EC
1108/82). Analysis of the samples was performed in duplicate; the coefficient of
variation was always below 10 %.

8.3 Recommendations
There are many methods available for the analysis of sulphites in foods and the
decision as to what method should be used depends on the expected level of
sulphite and the matrix to be analysed. Further method development is required to
establish methods for determining sulphite in cabbage, dried garlic, dried onions,
leeks and soy proteins as two of the standard methods are not applicable to these
2,6
matrices.