Last updated on 11 December 2001

Survey of Meat Content, Added Water and Hydrolysed Protein in Catering Chicken Breasts (Number 20/01)

Food Survey Information Sheet

This survey was conducted as part of the Agency's food authenticity programme, which aims to gather information about the description of food in the UK.

Summary

The Food Standards Agency and 22 Local Authorities have conducted a joint exercise to investigate the meat content, added water and hydrolysed protein in chicken breasts supplied to the catering trade. These products are bulk-packed (10kg) frozen, skinless chicken breasts with added water and other ingredients. Sixty-eight samples were collected by Enforcement Officers and analysed in Public Analyst Laboratories. The following was found:

  • 31 (46 percent) samples had a determined meat content of between 5 percent and 26 percent less than that declared on the packaging;
  • 32 (47 percent) had a determined meat content within plus or minus 5 percent of that declared;
  • 5 (7 percent) had a determined meat content greater than 5 percent of that declared;
  • Added water in the samples ranged from zero up to 43 percent.
  • 8 (12 percent) samples used quality descriptions taken from the Poultry Meat Marketing Standards reserved for chicken breasts without any added ingredients;
  • Elevated hydroxyproline levels indicated the use of hydrolysed proteins derived from collagen in 16 (24 percent) of the samples, with only two samples labelled as containing hydrolysed protein;
  • Two samples tested positive for pork DNA.

The results of the survey show that the labelling of many catering chicken breasts is misleading. Food labelling regulations require that descriptions should match their composition and all ingredients should be accurately declared.

Background

This survey has been conducted as a follow up to the “Survey on Added Water in Chicken and Chicken Parts” reported by the Food Standards Agency in October 20011, in which a group of chicken breast samples were found to contain added water at levels exceeding 30 percent.

Trading Standards Officers have also conducted investigations following customer complaints about the quality of chicken in restaurant and take-away meals and a number of prosecutions have been carried out against wholesalers who supply chicken breasts to the catering trade.

Concerns have been expressed to the Food Standards Agency that undeclared hydrolysed protein supposedly derived from chicken collagen, but possibly from other animal species, is being added during the processing of the chicken breasts in order to aid added water retention and increase the apparent meat content.

In response to these concerns the Food Standards Agency and 22 Local Authorities conducted a joint exercise to investigate the meat content, added water and hydrolysed protein in chicken breasts supplied to the catering trade. The products purchased were bulk-packed (10kg) frozen, skinless chicken breasts with added water and other ingredients.

Legislation
The European Commission has introduced Marketing Standards for Poultrymeat2 in order to facilitate trade and to ensure EU consumers are provided with good quality fresh and frozen poultrymeat produced to a common standard. These Regulations apply to fresh, chilled or frozen whole carcasses, parts and offal of poultry and relate to the classification by quality, weight, packaging (including labelling), water content and storage. They require slaughterhouses to comply with limits for the “technically unavoidable water content”, which arise during processing. The Regulations do not apply to prepared or preserved poultry which has been cooked, processed, treated or incorporated into recipe dishes, and do not include the products which were the subject of this survey i.e. skinless chicken breasts with added water, salts, sugars, flavourings and water retaining additives.

Up until February 2000, whole chickens or cuts of chicken where an ingredient, other than additives, water, self-basting preparations or seasonings, has been added were subject to the provisions of the Meat Products and Spreadable Fish Products Regulations 19843(MPSFPR), as amended. The Regulations required such products to declare the minimum meat content. This requirement has now been superseded by the provisions of the Food Labelling Regulations 19964. Prepacked products are now subject to quantitative ingredient declaration labelling (QUID provisions) and must be labelled with a percentage of the characterising or named meat species mentioned in the name of the food.

Processing of chicken breasts
A range of chicken breast products are sold to the catering sector, from cuts containing no added water, other than that unavoidably incorporated during preparation and freezing, to skinless and boneless chicken breasts to which water and other ingredients have been added. It was this latter type of product that was examined in this survey.

The chicken breasts used for this type of product generally originate from third countries, where up to 1.5 percent dry salt is added prior to freezing. This treatment allows them to be imported into the European Union under a reduced import tariff. European producers then incorporate added water into the chicken meat by tumbling the defrosted chicken breasts under vacuum with solutions containing salt and polyphosphates, which help to retain the water in the meat. Other additives and ingredients are also included at this stage, such as antioxidants, sugars, flavour enhancers and flavourings. The amount of water incorporated into the meat is controlled by the amount of water initially added to the tumbler and the tumbling time. Following processing, the chicken breasts are packed into 10kg boxes and frozen prior to despatch to distribution centres and cash and carry outlets. Higher amounts of added water can be achieved by injecting a solution of the water retaining agents into the chicken breasts with or without further tumbling.

Methodology

Sampling
The majority of the 68 samples of bulk-packed frozen skinless and boneless chicken breasts were purchased during July and August 2001 from cash and carries, distribution centres and one manufacturing site in 22 different regions of the UK. One sample however was collected in April 2001 and submitted for inclusion in the survey. The samples were collected by Enforcement Officers from the following local authorities: Aberdeen, Bath and North East Somerset, Belfast, Derbyshire, Hampshire, Kingston-upon-Hull, Leicestershire, Lincolnshire, London Borough of Brent, London Borough of Croydon, Manchester, Newport, Nottingham City, Nottinghamshire, North East Lincolnshire, North Yorkshire, Poole, Sandwell, Tameside, West Yorkshire, Wolverhampton and Worcestershire.

The collecting officers were provided with a written sampling protocol and sampling plan detailing the type of samples required and the product information to be recorded on a specially designed sample collection form. Details of the samples collected are included in Table 1 (See below).

Analytical Approach
Each sample was analysed for nitrogen, moisture, fat, ash and hydroxyproline by one of thirteen Public Analyst Laboratories using internationally accepted methods or approved equivalents outlined in an analytical protocol provided by the Food Standards Agency. As a quality control check, each laboratory was required to analyse, in duplicate, in each batch a reference material from Round 27 of the Food Analysis Performance Assessment Scheme (FAPAS) series 1 with assigned levels of the above analytes. For the results of the analysis to be accepted, measurements obtained from the analysis of the FAPAS reference material had to be within two standard deviations of the assigned value and the duplicate analyses had to be within the repeatability characteristics of the method. The data generated for the analysis of the materials was also used to calculate the method uncertainty applied to the results.

Determination of meat content

The determination of the meat content of a meat product is based on the approach originally elaborated by Stubbs and More5 and involves the analysis of the sample for nitrogen, moisture, fat and ash. The data derived from the analysis is first used to calculate the apparent fat-free meat content as follows.

Apparent Fat-Free Meat Content = Total Nitrogen/NF x 100

Where NF is the nitrogen factor associated with the product analysed. For this survey a nitrogen factor of 3.85 for lean breast meat was used as recommended by the Analytical Methods Committee (AMC) in its recent report on nitrogen factors for chicken meat6.

The measured fat content is then added to this figure to give the apparent total meat content.

Apparent Total Meat Content = Apparent Fat-Free Meat Content + fat

Determination of added hydrolysed protein

Collagen, which is a major structural protein found in skin, bones and other connective tissue, is characterised by a unique amino acid hydroxyproline. Hydrolysed protein derived from collagen will be high in hydroxyproline. Skinless chicken breast on the other hand has a relatively low level of collagen, and hence a low hydroxyproline level. Hydrolysed protein from collagen was considered to be present in a sample if the determined hydroxyproline was higher than that naturally associated with lean chicken breast. AMC data for hydroxyproline in lean skinless chicken breast is 0.08 percent6. Proteins derived from sources other than collagen were not tested for in this survey.

The calculation for the apparent total meat content as used above assumes that all of the determined nitrogen is derived from the chicken muscle. Therefore it was necessary to make a correction to the apparent total meat content if excess hydroxyproline was present.

Factors have been derived7 that allow the percent nitrogen contributed by any collagen in a sample to be calculated from the hydroxyproline as follows:

Collagen Nitrogen = excess hydroxyproline x 1.28

The percent collagen nitrogen was then deducted from the percent total nitrogen and the apparent total meat content calculated as above.

Estimation of added water

An estimate of the amount of added water can be made by subtracting the meat content and all the added ingredients from 100 using the following equation.

Added water = 100 - (Apparent Total Meat Content + salt + carbohydrate + other ingredients)

Where the carbohydrate is calculated by difference:
Carbohydrate = 100 - (protein + fat + ash + moisture)

In this survey the added water was estimated using the equation;

Added water = 100 - (Apparent Total Meat Content + ash + carbohydrate)

Determination of the species origin of added ingredients

In order to determine if any of the ingredients used were derived from other animal species, a Public Analyst Laboratory performed DNA analysis using an in-house method.

The method is based on the polymerase chain reaction (PCR), which amplifies species specific fragments of DNA using short sequences of DNA known as primers. Following PCR, the amplified DNA fragments are separated according to their molecular weight on a polyacrylamide gel and appear as bands when subjected to ultra violet light. DNA from particular species can then be identified by comparison with standards. For the analysis of the survey samples, primers that amplify fragments unique to beef or pork as well as primers that amplify a cross species fragment were used.

With each batch of test samples the following standards and controls were included; a water blank, 100 percent chicken standard, 100 percent pork (or beef) standard, 2.5 percent Pork (or beef) standard 1.0 percent pork (or beef) standard.

For a batch to be accepted, no bands should be seen on the gel for the water blank, and bands corresponding to the particular species should be seen on the gel for the beef and pork standards.

A band corresponding to the cross species fragment should be seen on the gel for each of the standards and samples, this indicates that the DNA extracted from the samples was successfully amplified during the PCR. If no band was seen the sample was repeated.

Any bands present on the gel for a test sample corresponding to beef or pork indicated that DNA from that species was present in the sample. The test is not quantitative.

Results and Discussion

All of the laboratories returned satisfactory performance data for the analysis of the FAPAS material. The calculated values for determined meat content, the difference between the declared and determined meat content and the estimated added water are given in Table 1, below.

The average measurement uncertainty associated with the determined meat content was calculated as 2.7 percent. When this value is applied to each result, a range of values is given within which the true value is expected to lie with a level of confidence of 95 percent. Taking this into account samples where considered to be misdescribed if the determined meat content was 5 percent less than that declared.

A summary of the results comparing the apparent meat content and the declared meat content were as follows:

  • 31 (46 percent) samples had a determined meat content of between 5 percent and 26 percent less than that declared on the packaging;
  • 32 (47 percent) had a determined meat content within plus or minus 5 percent of that declared;
  • 5 (7 percent) had a determined meat content greater than 5 percent of that declared;
  • Added water ranged from zero up to 43 percent.

Sixteen samples were found to contain excess hydroxyproline, which indicated that hydrolysed protein derived from collagen was present. The amount of excess hydroxyproline ranged from 0.05 to 0.36 g/100g and contributed between 1.7 percent and 12 percent to the determined meat content.

Four samples were described as chicken breast fillets, and neither a meat content declaration, nor ingredients list was given. These samples, therefore, should comply with the limits for the “technically unavoidable water content” in the Poultry Meat Marketing Regulations. One of these samples had an estimated added water content of 13 percent, which exceeds the limit for "technologically unavoidable water content" of 2 percent for lean chicken breast fillets laid down in the Poultry Meat Marketing Regulations.

The remainder of the samples tested however indicated that water had been added either in their description or in their ingredients list. Eight samples used the description “Grade A”, which is a quality term reserved for products complying with the Poultrymeat Marketing Regulations i.e. for chicken only having technically unavoidable water within specified limits not added water with ingredients. In addition, although these remaining 64 samples are required to give a percentage chicken declaration under the QUID requirements of the Food Labelling Regulations many gave a minimum % meat content (as required by the Meat Products and Spreadable Fish Products Regulations 1984).

The majority of the products listed E621 mono sodium glutamate (MSG) and E640 glycine in the ingredients list as flavour enhancers. These are both amino acids (or their derivatives), which contain nitrogen, and would contribute to the percent total nitrogen determined (for example 1 percent MSG would contribute approximately 2 percent to the determined meat content). One sample also listed casein, a milk protein, in the ingredients list. No allowance was made for the presence of these additives in the calculation of the total meat content of the samples.

Pork DNA was detected in two samples (WC004 and KUH001), but no beef DNA was detected in any of the samples.

Conclusions

The results of the survey show that in many of the samples examined the labelling was misleading either in the description given, the ingredients added or the meat content. Food labelling regulations require that descriptions should match their composition and all ingredients should be accurately declared. The determination of meat content showed that over half of the samples analysed had an actual meat content that differed from the declared meat content by greater than 5 percent. The description of some of the products as 'grade A' should be confined to the Poultry Meat Marketing Standards and should therefore not be used for chicken products with added water and ingredients.

Evidence of the use of hydrolysed proteins from collagen was found in 16 (24 percent) of the samples, with only two labelled as containing hydrolysed protein.

Two of the samples tested positive for the presence of pork DNA indicating that ingredients from sources other than chicken had been used.

Trading Standards Departments have been informed of the results of the analysis of the samples that they collected to enable them to carry out any follow up action that they consider appropriate.

The companies whose samples had a determined meat content that differed by more than 5 percent of that declared on the packaging were given the opportunity to comment on the results of the analysis. Companies were also asked to comment if the use of hydrolysed proteins was indicated by the presence of excess hydroxyproline or the presence of ingredients derived from pork was indicated by the DNA analysis. Comments received are reproduced in Annex 1, below.

References

  • 1. Food Standards Agency, Survey of added water in chickens and chicken parts, Food Surveillance Information Sheet No. 8/00, October 2000.
  • 2. Commission Regulation 1538/91 introducing detailed rules for implementing Council Regulation (EEC) 1906/90 on Certain Marketing Standards for Poultry. Official Journal of the European Communities, 1991, L143.
  • 3. Meat Products and Spreadable Fish Products Regulations 1984, as amended. Statutory Instrument 1984 No. 1566. 1984, London: HMSO, 1984.
  • 4. The Food Labelling Regulations 1996, as amended. Statutory Instrument 1996 No. 1499. London: HMSO, 1996.
  • 5. Stubbs, G. and More, A. (1919) the estimation of the approximate quantity of meat in sausages and meat pastes. The Analyst , 44, 125.
  • 6. Report by the Analytical Methods Committee Nitrogen factors for chicken meat (2000), The Analyst, 125, 1359-1366
  • 7. Lord, D.W. and Swan, K.J. (1984) Connective tissue in beefburgers. Journal of the Association of Public Analysts, 22 (4), 131-140

Further Information

Dr Mark Woolfe
Food Standards Agency
Food Labelling and Standards Division
Room 123, Aviation House
125 Kingsway
WC2B 6NH
Tel: +44 (0) 20 7276 8176
Fax: +44 (0) 20 7276 8193
E-mail:mark.woolfe@foodstandards.gsi.gov.uk

or

Mr Martin Sams
Food Standards Agency
Food Labelling and Standards Division
Room 115C, Aviation House
125 Kingsway
WC2B 6NH
Tel: +44 (0) 20 7276 8150
Fax: +44 (0) 20 7276 8193
E-mail:martin.sams@foodstandards.gsi.gov.uk