A03042: Substances migrating from ion-exchange resins

Study Duration: April 2003 to August 2004

Contractor: Rapra Technology Ltd

Ion-exchange resins are used to remove or isolate specific ions or ionisable species from water and food products during processing stages in their manufacture. To date, there is no EU harmonised legislation for such resins as food contact materials. However, Annexe 1 to the new Framework Regulation for food-contact materials (1935/2004/EC) includes ion-exchange resins within a list of groups of materials and articles that may be covered by specific measures.

In addition, the Council of Europe has issued a resolution on ion-exchange resins (AP 97/1). This is not a legally binding document but members of the Partial Agreement in the Social and Public Health Field, such as the United Kingdom, are expected to take note of such resolutions.

Included in the resolution is an inventory list of substances used in the manufacture of ion-exchange resins and a migration limit of 1mg/litre total organic carbon in the 5th bed volume (water) rinse solution. In the USA, a list of ion-exchange resins authorised for food-contact use, together with some restrictions, is given in the FDA regulations (Title 21, Section 173.25).

The aim of this project was to provide background information on the use of ion exchange resins and to determine possible migrants from such uses, with a view to informing future negotiations on possible EU legislation. The objectives were to determine:

• the main types of ion-exchange resins currently used in contact with food
• the major applications of ion-exchange resins used in contact with food
• typical usage conditions
• the nature of potential migrants from the resins
• whether standard EU food simulants are suitable for migration testing or whether testing should be undertaken in more acidic or alkaline solution to reflect the use of the resins
• whether regeneration introduces resin breakdown and potential migratory species
• the effect of resin misuse on potential migrants
• whether testing leachable substances in the 5th bed volume is adequate (as required by the Council of Europe Resolution on ion-exchange resins)
• whether or not migrating species from ion-exchange resins can be detected in food

The approach taken has included desk research, discussions with resin suppliers, and visits to and contacts with the food industry. The main part of the research has been a detailed analytical testing programme on six types of ion exchange resin, representative of resin types used commercially. Extractable ionic and organic substances have been examined using combined liquid chromatography/mass spectrometry (LC-MS) and gas chromatography/mass spectrometry (GC-MS).

Applications of ion-exchange resins
The main applications of ion-exchange resins in food processing have been identified as treatments of: water, sugar (decolourisation or demineralisation), wines and spirits, milk and dairy products (isolation of proteins), soft drinks and fruit juices. Of these, treatment of water for use with food products is the largest application. However, at present there is developing interest in the use of ion-exchange resins for the isolation of proteins, including enzymes from milk and other products.

Typical usage conditions
Observations made during factory visits were that the large resin beds employed are subject to continual use and regeneration over many years with adequate performance. Companies are reluctant to change resins in the shorter term, on cost grounds. Some resins are operated at elevated temperatures.

Potential extractables
Extractable material from new, non-rinsed resins varied with resin type and, where detected, largely comprised water-soluble ionic substances from functionalisation of the resin, non-ionic oxidation products and organic solvent-soluble, non cross-linked, low molecular weight resin. Ionisable extractables, including oxidation products, were generally removed by rinsing the resin with water and/or water containing 10% ethanol.

Suitability of the standard EU food simulants for migration testing
Methods used in this research for examining specific migration of ionic substances should be suitable for all three EU aqueous food simulants. For non-ionic organic substances, liquid chromatography mass spectrometry (LC-MS) methods could also be used with the alternative fatty food simulant 95% ethanol and gas chromatography mass spectrometry (GC-MS) methods with isooctane. Stronger acids and alkalies are only used in resin regeneration. Due to the need for washing resins after treatment, it is not considered necessary to undertake migration testing in more acidic or alkaline solutions. No applications of ion-exchange resins where olive oil would be the required simulant were identified.

Testing leachable substances in the 5th bed volume
The Council of Europe (COE) Resolution on ion-exchange resins (AP97/1) requires levels of total organic carbon to be less than 1 mg/kg in the 5th bed volume rinse. This is consistent with industrial practice for washing resins with four bed volumes of potable water after installation or after regeneration. In contrast, repeat use food contact plastic materials are normally subjected to migration testing on a third extraction. Test data obtained on the third extraction indicated that some substances could be detected at levels above 10µg/kg, but they were greatly reduced by the fifth extraction.

Based on this and in view of the long lifetimes of ion-exchange resins and the high volumes of water or foodstuff passing through, testing migration in the 5th bed volume as adopted by the COE would appear to be more appropriate than the 3rd bed volume.

Effects of resin regeneration on potential migratory species
In the tests undertaken where resins were left in contact with sodium hydroxide for 10 days at 70°C, no new migratory species were detected from washed, neutralised resins.

Resin misuse
Companies working to the principles of 'good manufacturing practice' should avoid resin misuse. No new peaks were identified in the resins heat-aged in an oven for 10 days at 70°C.

Migration into food
Further work could refine the methodology used with food simulants to examine any specific migration from ion-exchange resins into food.

In summary, while a number of potential migrants were identified in the resin extracts, these were easily removed by washing. Good manufacturing practice must be followed in order to avoid resin mis-use and ensure that the resin is well washed. For the ion-exchange resins investigated, the levels of all potential migrants were greatly reduced by the 5th bed volume – this endorses the COE recommendation for testing on the 5th bed volume.

The 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 ( tel: 020 7276 8181/8182 or email: library&info@foodstandards.gsi.gov.uk )

Contact: Email: science@foodstandards.gsi.gov.uk