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Listen to this siteWednesday 18 June 2003
This research project aims to identify the chemicals present in cork stoppers and estimate the amounts that could migrate into foods.
Study Duration : April 1998 to March 2003
Contractor : Central Science Laboratory
As well as classical cork stoppers, a wide range of other products is now used. Alternatives to natural corks are agglomerate corks (manufactured using ground cork which is bound together with adhesives and other substances), colmated corks (lower quality natural corks which have large cracks and holes which are filled with a mixture of cork dust and adhesive), semi-synthetic and synthetic stoppers.
As the variety of stoppers used in contact with foods increases the number of potential contaminants rises. Corks for wines are generally printed or burned to ‘brand’ the product and then given a surface finish. Some corks are dyed to improve their appearance. In addition, adhesive components and their transformation products, and any contaminants of these stoppers may transfer to foods. Polyurethane adhesives may be used for binding the ground cork together in agglomerate corks. These adhesives are made from isocyanate monomers (which may hydrolyse to amines) and a polyhydroxy substance such as propylene glycol or polyether or polyester polyols.
The aim of this project was to determine the identity of potential contaminants from agglomerate, synthetic and natural cork stoppers and to establish any migration that may occur.
A shelf audit of retail outlets was undertaken to establish the types of closures in common use and their applications. In addition a variety of natural cork stoppers, agglomerate corks, champagne type corks (agglomerate corks with two natural cork discs), 1+1 corks (agglomerate with a cork disc at either end), colmated corks and synthetic stoppers, along with several substances used in cork manufacture, were obtained from industry. Solvent extracts of the samples were analysed by gas chromatography-mass spectrometry, liquid chromatography-particle beam-mass spectrometry and direct-insertion probe-mass spectrometry, and direct-insertion probe-mass spectrometry. The migration of those substances detected in the solvent extracts was determined along with the total migrate which was determined gravimetrically.
The stoppers were analysed for extractable isocyanates as residual monomers from any polyurethane binder used and for the hydrolysis products of aromatic isocyanates, primary aromatic amines.
The levels of elements (Li, Na, Mg, Al, P, K, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Mo, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Eu, Gd, Ho, Er, Yb, W, Pb, Th and U) in the stoppers were determined and in all cases the worst case migration potential was determined.
Solvent extracts of 16 representative corks/stoppers and 13 samples of chemicals used in the manufacture of stoppers were analysed. These initial screening studies detected a range of compounds in the total ion chromatograms of the extracts and their identities were proposed by comparison with Wiley library spectra. The levels of these compounds migrating into 15% ethanol following exposure at 40°C for 1 month were estimated semi-quantitatively. Several compounds were detected in the migration simulant following exposure. Amongst the compounds identified were alkanes derived from mineral hydrocarbons. The Food Standards Agency recently published a survey on mineral hydrocarbons in food contact materials (FSIS 34/03). Materials investigated included cork stoppers. This survey established that the migration of mineral hydrocarbons into food is not a health concern. Specific analysis for extractable isocyanates as residual monomers from any polyurethane binders used did not detect the presence of these compounds and nor were primary aromatic amines, derived from aromatic isocyanates, detected. The maximum levels of metals that could migrate were calculated and in the unlikely event of total extraction of metal ions into the wine the levels would have been less than those present in the wines themselves.
This project has identified the potential migrants present in 16 representative stoppers intended for food contact applications. The levels of these substances in the stoppers and in food simulants exposed to the stoppers, were generally low.
Final report is available from the FSA Library and Information centre. To obtain a copy, please contact the Enquiry Desk, Dr. Elsie Widdowson Library and Information Services, Food Standards Agency (020 7276 8181/8182 or at infocentre@foodstandards.gsi.gov.uk ).
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