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The information in the archive was published by MAFF, Department of Health and the Scottish Executive before April 1st 2000 when the Food Standards Agency was established.

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Food Surveillance Information Sheet


Number 182     July 1999

MAFF UK - TIN IN CANNED PINEAPPLES


Index to MAFF UK Food Surveillance Information Sheets, 1999

See also:
122: MAFF UK - Survey of Lead and Tin in Canned Fruits and Vegetables (August 1997)
131: MAFF UK - 1991 Total Diet Study - Metals and Other Elements (November 1997)
146: MAFF UK - Concentrations of Metals and Other Elements in Selected Snack and Convenience Foods (March 1998)
149: MAFF UK - 1994 Total Diet Study (Part 2) Dietary Intakes of Metals and Other Elements (May 1998)
150: MAFF UK - Metals and Other Elements in Cows' Milk and Vegetables Produced Near Industrial Sites (May 1998)
151: MAFF UK - Concentrations of Metals and Other Elements in Marine Fish and Shellfish (May 1998)
152: MAFF UK - Summaries of Food Surveillance Papers - 'Lead, Arsenic and Other Metals in Food' and 'Cadmium, Mercury and Other Metals in Food' (June 1998)
155: MAFF UK - Lead in Dried Fruit (August 1998)
166: MAFF UK - Metals and Other Elements in Vegetarian Foods (November 1998)
179: MAFF UK - Tin in Canned Tomato Products (June 1999)

  • This survey was carried out to check the levels of tin in canned pineapples on sale in the UK following a report from the European Commission that elevated tin concentrations had been found in some batches of canned pineapples imported into Finland. High tin concentrations in food may cause short-term stomach upsets in some people but without any lasting harm.
  • Tin concentrations in all 100 products tested were within the expected range and below the UK legal limit of 200 mg/kg for tin in food.
  • The tin concentrations found in these products do not present any concerns for consumers' health.
Summary

A survey of tin in a wide range of canned pineapple products on sale in the UK was carried out between January and March 1999. The purpose of the survey was to determine the tin concentrations in these products and to see whether any products were affected by a problem of high tin concentrations, identified in certain batches of canned pineapples tested by authorities in Finland in late 1998. High tin concentrations in food may cause short-term health effects in some people, including stomach upsets, abdominal cramps, nausea and/or diarrhoea.

Tin concentrations were measured in three separate cans from the same batch for each product tested and the mean (average) tin concentration across the three cans was used to determine whether the batch was affected by elevated tin levels. The tin concentrations found were similar to those normally expected in these products and mean tin concentrations in all products were below the legal limit of 200 mg/kg for tin in food set by the Tin in Food Regulations 1992 (S.I. [1992] No. 496).1

For several samples the tin concentrations varied quite widely between individual cans from the same production batch, by 50 mg/kg or more in some cases. In one sample, one individual can had a tin content (at 210 mg/kg) just above the limit while the other two cans had tin contents (119 mg/kg and 124 mg/kg) well below the limit. The mean tin content in this product (151 mg/kg) was below the 200 mg/kg legal limit, as with all the other products tested. JFSSG has asked the supplier of this product to investigate these results. This supplier was also invited to submit a brief statement on their results for inclusion in this Food Surveillance Information Sheet but did not do so.

Background

Health effects of tin in food
High concentrations of tin in food irritate the gastrointestinal tract and may cause stomach upsets in some individuals, with symptoms which include nausea, vomiting, diarrhoea, abdominal cramps, abdominal bloating, fever and headache. These are short-term effects with recovery expected soon after exposure.2 These effects may occur in some individuals at tin concentrations above 200 mg/kg with an increased risk of effects at concentrations above 250 mg/kg. Long-term effects are not expected from tin in the diet.2

As there are health concerns regarding high concentrations of tin in food, regulations have been established setting a maximum limit of 200 mg/kg for tin in foods sold in the UK. These are the Tin in Food Regulations 1992 (S.I. [1992] No. 496).1 The Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) gives the Government independent expert advice on the safety of chemicals in food and has supported this limit, intended to protect consumers against the potential adverse effects of high concentrations of tin in food.2

The Joint Expert Committee on Food Additives of the Food and Agriculture Organization and the World Health Organization (JECFA) has recommended a Provisional Tolerable Weekly Intake (PTWI) for tin of 14 mg/kg body weight/week to protect against the risk of any chronic (long-term) effects.3 This PTWI is equivalent to 120 mg/day for a 60 kg person. The PTWI is an estimate of the amount of a substance that can be ingested over a lifetime without appreciable risk to health.

Most foods contain very low concentrations of tin, usually below 10 mg/kg, although canned foods may contain higher concentrations as a result of the slow dissolution of the tin coating used on the inside of some food cans to protect the steel body of the can from corrosion. In the 1994 Total Diet Study (TDS), which is the most recently reported of JFSSG's TDSs on the levels of metals in the UK diet, average tin concentrations in all food groups were below 1 mg/kg, except for Canned vegetables (44 mg/kg tin) and Fruit products (which includes canned fruits; 17 mg/kg tin).4 Together, the Canned vegetables and Fruit products groups accounted for 97 per cent of the dietary exposure of the general UK population to tin of 2.4 mg/day, estimated from this survey.4 This total exposure represents only 2 per cent of the JECFA PTWI for tin, which supports the view that long-term health effects are not expected from tin in the diet.3

Tin in canned foods
Many factors influence the amount of tin that is taken up by canned foods from the internal coating of the can. These include: the type and composition of the product itself (including the acidity, the presence of organic acids and pigments and certain ions such as nitrate); the type of can (including the quality and thickness of the tin coating, the amount of the tin coating that is exposed to the can contents and the presence or absence of a layer of lacquer over the tin plate); the canning procedure (including the amount of air in the container at sealing and the internal vacuum and 'headspace' between the fill level of the product and the lid) and storage (time from canning and temperature during storage).5

Under normal circumstances the shelf life of canned foods is set so that the tin content of the food remains well below the legal limit throughout the product's shelf life. However, under certain circumstances tin dissolution can accelerate causing unacceptably high tin concentrations in the food within its shelf life.

A problem with elevated tin concentrations in some batches of canned tomatoes and canned pasta in tomato sauce was discovered recently in a JFSSG research project6,7 and in subsequent tests by JFSSG, industry and enforcement authorities in Scotland and England.8,9 Further details of this problem and the results of JFSSG's recent survey of tin in canned tomato products were published in June 1999 in Food Surveillance Information Sheet No.179.9 The final report of the JFSSG research project 'Investigation of Sources of Tin in Canned Foods' is available to the public in MAFF's library6,7 (see 'Further Information').

In late December 1998, JFSSG was informed via the European Commission that elevated concentrations of tin had been found in some batches of canned pineapples imported into Finland and tested by the Finnish authorities. Since there are health concerns associated with elevated concentrations of tin in food, JFSSG commissioned this extensive survey of tin in canned pineapples on sale in the UK to check whether any of these products were affected by this problem. The survey was carried out on behalf of JFSSG by Campden & Chorleywood Food Research Association (CCFRA).

Brand names
In accordance with the MAFF policy for the release of brand names when reporting the results of food chemical surveillance,10 details of the individual samples of canned pineapples tested in this survey are given in full in Table 1. It should be noted that the absence of any particular brand from this survey means only that the brand has not been included in the survey. No further meaning should be read into the absence of any product or brand from this Food Surveillance Information Sheet.

Methodology

Sample plan
The sample plan was designed to cover the major product types, brands and retailers of canned pineapples, as well as smaller brands and retailers, according to available market share data.11,12 A total of 100 products were sampled including canned pineapple slices, pieces, chunks and rings, products packed in syrup and in juice, and different can sizes including smaller 'snack' type products.

Tin concentrations in canned foods can vary considerably between individual cans in the same production batch. Therefore, tin concentrations were measured in three separate cans from the same batch for each product sampled and the mean (average) tin concentration for the three cans was used to determine whether the batch was affected by elevated tin levels. Each sample consisted of four cans with identical batch codes (three for analysis and one held in reserve for possible future examination), giving a total of 400 cans.

Samples were purchased by CCFRA from retail outlets in three geographical areas of England: the north (Humberside area), the Midlands, and the south-west (Cornwall). This spread was intended to ensure that brands more common in particular areas were represented as well as brands distributed nationally. The survey was not designed to examine whether there were any differences between tin concentrations in these products in different regions and this aspect is not discussed further. Further details of the sampling plan and sample instructions are given in the contractor's final report for this survey,13 which is available to the public in MAFF's Library (see under 'Further Information' below).

Sample preparation and analysis
For each product sampled, three individual cans were analysed separately for tin with the fourth can being retained for possible future examination. Cans for analysis were opened and the contents transferred immediately to a sealed glass or plastic vessel (samples were not left in the cans after opening). The entire can contents were homogenised prior to analysis and the tin content was determined by a method based on flame atomic absorption spectrophotometry. The emptied cans were immediately cleaned and dried and stored under stable conditions for future reference. All cans analysed were within their 'best before' dates when they were opened.

The internal vacuum and headspace depth (which indicates the filling level) of each can were also measured on opening. These parameters can be used to check whether any anomalies have occurred during the canning procedure that might cause elevated tin concentrations. To check any influence of the can type and the quality of the internal coating on tin concentrations in the food, the internal surfaces of the empty cans were inspected visually and the type and condition of internal coating (e.g. tin plate only, partial or complete lacquered coating) were recorded for each can.

Analytical Quality Assurance
CCFRA is accredited by the United Kingdom Accreditation Service (UKAS) for the determination of tin in food by the method used in this survey. CCFRA has taken part in all rounds of the Food Analysis Performance Assessment Scheme (FAPAS) for tin and has consistently performed well. The method used has a limit of detection (LOD) of 5 mg/kg and a repeatability of plus or minus 5.0 mg/kg at tin concentrations below 100 mg/kg and plus or minus 5 per cent (relative) at tin concentrations above 100 mg/kg. All samples were analysed in duplicate and duplicate results falling outside these repeatability criteria were rejected and the analyses repeated. However, repeatability for duplicate samples in this work was typically less than 1 per cent (relative). Each batch of analyses included at least one spiked sample, the recovery of which had to fall between 85-115 per cent, otherwise all analyses in the batch had to be repeated. In this survey, the requirement for recovery concentrations was met in all cases.

Results

Tin was detected in all samples tested with the mean tin concentration for all samples being 70 mg/kg (range 11 mg/kg to 210 mg/kg). Full details of the individual products tested, including brand names and batch numbers are given in Table 1, together with the tin concentrations found in each of the individual cans and the mean tin concentration for each product tested. All results are reported on a wet weight basis (i.e. as purchased).

Interpretation

Tin concentrations were similar to those found in previous studies4,14 and mean tin concentrations were within the legal limit of 200 mg/kg for tin in food in all products tested. The overall mean concentration in all 100 samples tested in this survey is 70 mg/kg. This is very similar to the mean tin concentration of 72 mg/kg found in nine composite samples of canned pineapples tested in an earlier MAFF survey of canned foods,14 but higher than the mean of 17 mg/kg found in the Fruit products food group in the 1994 TDS4 (of which canned fruit products make up a large proportion). This is as expected and reflects the fact that the TDS Fruit products group comprises composite samples which include foods which are not canned and hence contain much lower concentrations of tin, whereas the present survey focused on canned pineapples which are known to have a potential to accumulate higher tin concentrations.

There was no obvious relationship between tin content and the headspace depth or vacuum in the can.13 There was also very little difference in the mean tin content of products packed in juice (68 mg/kg, 52 products) and those packed in syrup (73 mg/kg, 48 products). Only five products tested (5 per cent) were packed in fully lacquered cans (which have no exposed tin on the interior of the can) and as expected these had a lower mean tin content (28 mg/kg, 5 products) than those in unlacquered or partially lacquered cans (72 mg/kg, 95 products).

For several samples the tin concentrations varied quite widely between individual cans from the same production batch, by 50 mg/kg or more in some cases. In one sample, one individual can had a tin content (at 210 mg/kg) just above the limit while the other two cans had tin contents (119 mg/kg and 124 mg/kg) well below the limit. The mean tin content in this product (151 mg/kg) was below the 200 mg/kg legal limit, as with all the other products tested. JFSSG asked the supplier of this product to investigate these results. This supplier was also invited to submit a brief statement on these results for inclusion in this Food Surveillance Information Sheet but did not do so.

Long-term exposure to tin in the diet
As noted above, tin in the diet is not known to cause any chronic (long-term) effects on health. Nevertheless, JECFA has recommended a PTWI to help protect against any risk of long-term effects of dietary exposure to tin. Long-term dietary exposures to tin from the products tested in this survey were therefore estimated. This was done by assuming that all canned fruit products contain tin at the mean concentration reported for canned pineapples in this survey (70 mg/kg) and that all other foods contain tin at the mean concentrations found in the 1994 TDS,4 and using data on the patterns and amounts of different foods eaten by UK adult consumers from the National Dietary and Nutritional Survey of British Adults (NDNS).15 The data from the NDNS allow exposure to be estimated both for average consumers and for 'upper-range' consumers who have higher dietary exposures because they eat above-average quantities of particular foods.

The total dietary exposures to tin estimated on this basis were 2.8 mg/day for an average adult consumer and 9.0 mg/day for an 'upper-range' (97.5th percentile) adult consumer. These dietary exposures are well below the PTWI for tin which is equivalent to 120 mg/day for a 60 kg person, and are very similar to the exposures of 2.4 mg/day for the average and 7.9 mg/day for 'upper-range' (97.5th percentile) adult consumer estimated from the 1994 TDS.4 Therefore, the concentrations of tin found in this study are not a long-term health concern for consumers.

Conclusions

JFSSG has carried out an extensive survey of tin concentrations on canned pineapples on sale in the UK to check if these products were affected by a problem with elevated tin concentrations found in some batches of canned pineapples imported into and tested in Finland. The survey found no evidence that these products on sale in the UK are affected by elevated tin concentrations.

Actions
  • JFSSG has informed UK food safety enforcement authorities of these results.
Units
kilogram (kg): one thousand grams
milligram (mg): one thousandth of a gram
mg/kg: milligrams per kilogram (equivalent to parts per million)
mg/day milligrams per day
References
  1. The Tin in Food Regulations 1992 (S.I. [1992] No. 496). The Stationery Office, London.
  2. Ministry of Agriculture, Fisheries and Food (1998). Cadmium, Mercury and other Metals in Food. Food Surveillance Paper No.53. The Stationery Office, London.
  3. World Health Organization (1989). Toxicological evaluation of certain food additives and contaminants. Thirty-third meeting of the Joint FAO/WHO Expert Committee on Food Additives. WHO Food Additives Series:24. Cambridge University Press, Cambridge.
  4. Ministry of Agriculture, Fisheries and Food (1997). 1994 Total Diet Study: Metals and Other Elements. Food Surveillance Information Sheet No.131.
  5. Food and Agriculture Organization of the United Nations (1986). Guidelines for can manufacturers and food canners. Prevention of metal contamination of canned foods. FAO Food and Nutrition Paper No. 36. Food and Agriculture Organization of the United Nations, Rome.
  6. Campden & Chorleywood Food Research Association (1998). Investigation of Sources of Tin in Canned Foods. Final Report to MAFF, Campden & Chorleywood Food Research Association, Chipping Campden, Gloucestershire.
  7. Campden & Chorleywood Food Research Association (1999). Investigation of Sources of Tin in Canned Foods: Part Two. Final Report to MAFF, Campden & Chorleywood Food Research Association, Chipping Campden, Gloucestershire.
  8. Ministry of Agriculture, Fisheries and Food (1999). Tin in Canned Tomatoes. MAFF Press Release No. 456/98.
  9. Ministry of Agriculture, Fisheries and Food (1998). Tin in Canned Tomato Products. Food Surveillance Information Sheet No.179.
  10. Ministry of Agriculture, Fisheries and Food/ Department of Health (1997). Food Safety Information Bulletin No. 88.
  11. Mintel (1997). Frozen and canned fruit and vegetables, Market Intelligence: Food and Drink, June 1997. Mintel Ltd.
  12. Langley, R. (ed.) (1997). Canned Foods 1997. Keynote Plus Market Report, 11th Edition. Key Note Ltd.
  13. Campden & Chorleywood Food Research Association (1999). A Survey of Tin Content of Canned Pineapple Products. Final Report to MAFF, Campden & Chorleywood Food Research Association, Chipping Campden, Gloucestershire.
  14. Ministry of Agriculture, Fisheries and Food (1997). Survey of Lead and Tin in Canned Fruits and Vegetables. Food Surveillance Information Sheet No.122.
  15. Gregory, J., Foster, K., Tyler, H. and Wiseman, M. (1990). The Dietary and Nutritional Survey of British Adults. The Stationery Office.
Further Information

Further information on this survey can be obtained from:

Dr Patrick Miller
Joint Food Safety and Standards Group, MAFF
Food Contaminants Division
Room 238, Ergon House, c/o Nobel House
17 Smith Square
London SW1P 3JR

Tel: +44 (0) 20 7238 5751
Fax: +44 (0) 20 7238 5331
E-mail: pf.miller@fsci.maff.gov.uk

A copy of the final report of this survey has been placed in the MAFF Library, Nobel House, London, SW1P 3JR Tel. No. + 44 (0) 20 7238 6575. If you wish to consult a copy, please contact the library for an appointment giving at least 24 hours notice or alternatively copies can be obtained from the library: a charge will be made to cover photocopying and postage.


Spreadsheet tables

Table 1. Sample details and results for all samples of canned pineapples

Click here to view the Excel 5.0 version of Table 1
Click here to view the .csv version of Table 1 (if you have any other spreadsheet package)


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These pages were last updated on 30 June 1999

 
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