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.
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.
<p>Find more about this project and other FSA food safety-related projects at the <a href="http://www.food.gov.uk/science/research/" target="_blank">Food Standards Agency Research webpage</a>.