Authenticity issues in meat and meat products

PII:

SO309-1740(96)00072-l

Meat Science, Vol. 43, No. S, S277-S289, 1996 Copyright 0 1996 Published by Elsewier Science Ltd Printed in Great Britain. All rights resewed 0309-1740/96 S15.00+0.00

ELSEVIER

Authenticity Issues in Meat and Meat Products K. D. Hargin Ministry of Agriculture, Fisheries and Food, 320 Ergon House, 17 Smith Square,

London SWIP 3JR, UK

ABSTRACT Proper product description is of crucial importance in ensuring fair trading practices and enabling consumers to make informed choices and is therefore addressed in some detail in UK food legislation. This paper will briefly examine the historical development of UK food laws and the meaning of “authenticity” within the context of current legislation. particularly with respect to meat and fish products. The food authenticity programme of the UK Ministry of Agriculture, Fisheries and Food (MAFF) is discussed, outlining its R and D programme and detailing the types of topics under consideration, and how selection of surveillance projects is determined. Copyright 0 1996 Published by Elsevier Science Ltd

INTRODUCTION This paper sets out to highlight the principal types of authenticity issues that occur with meat and meat products. Since many of the problems are similar and much development work has been conducted in certain areas of fish authenticity, illustrations from this sector also will be included. Food authenticity issues in the form of adulteration and improper description have been around for a long time and probably for as long as food has been offered for sale. By the early 1800’s such problems were widespread and it was not uncommon for unscrupulous bakers or brewers to adulterate basic foodstuffs like bread and ale with chalk and sugar respectively. Historically, meat is not widely referenced as being a major contributor to the list of products usually associated with adulteration, probably because it was generally sold fresh and as easily recognisable joints, although veal was often whitened by the addition of chalk. Table 1 highlights some of the major milestones along the legislative path from the first Government inquiry, following reports in The Lancet on adulterated articles of food and drink (Hassall, 1855, 1857, 1876) culminating in our present Food Safety Act 1990. Up until 1875, however, the food and drugs laws were largely ineffectual since it was necessary to prove knowledge by the vendor that the goods were adulterated. This was rectified in 1875 with the introduction of the Sale of Food and Drugs Act 1875. Crucially, this made the appointment of public analysts compulsory and endeavoured to clarify what was meant by ‘adulteration’, and removed the requirement to prove ‘guilty knowledge’ on the part of the vendor, or that the adulteration was injurious to health. S277

K. D. Hargin

S278

TABLE 1

Milestones in UK food legislation history 1855-56

First Parliamentary Select Committee Inquiry into the adulteration drink (and drugs) as a result of agitation by consumers.

of food,

1857

First Bill introduced into the Commons embodying stringent legislation controlling adulteration practices with regard to food and drink. Strong opposition from all factions. Withdrawn.

1858

Two further Bills submitted-withdrawn

1858

October-“The Bradford Incident”: about 200 people poisoned, 17 fatally, from eating adulterated lozenges.

1859

Two further Bill submitted-changes becoming law.

1860

First General Act to prevent the adulteration of food and drink. Facilitated summary proceedings and appointment of public analysts. Act lacking enforcement apparatus therefore completely nugatory.

1872

Amendment

1875

Sale of Food and Drugs Act. Act enforceable.

1955

Food and Drugs Act

1984

Food Act

1990

Food Safety Act

for lack of support.

in government prevented either from

Act of 1872

There have been various amendments to the basic laws since the first Acts were passed but these fundamental principles of current legislation in the UK clearly owe their origins to the authenticity issues of the 18th and 19th century.

THE

MAFF

PROGRAMME

ON FOOD

AUTHENTICITY

In 1992 in the UK MAFF set up a formal programme on Food Authenticity. A Working Party was convened, consisting of representatives from enforcement authorities, industry, public analysts, consumer organisations as well as government officials, to assist and co-ordinate the programme, which included the commissioning of specific research and national surveys. MAFF’s funding of research projects to establish correct labelling of food and protection of the consumer stretches back quite a few years, though the last 10 years has seen a greater emphasis in these areas. Many of the projects have arisen out of the implementation of legislation in the UK, e.g. the use of nitrogen factors for the determination of added water in meat. The importance of authenticity methodology development also has been recognised and established within the food authenticity programme. The extent of this programme is highlighted in Table 2 which summarises the authenticity issues considered by the Working Party over the last five years in the meat and fish sectors. There are, of course, many other areas of authenticity research - meat and fish have not been singled out - and current research funding on all authenticity projects is of the order of El .2 million per annum. The remit of the Working Party is contained within its aims and terms of reference (Table 3). It is worth noting that the policy includes that authenticity activity in MAFF

S279

Authenticity issues

TABLE 2 Examples of different authenticity problems and methods of analysis Authenticity

Problem

Reference

Analytical Technique Nitrogent factors

Stubbs & More, 1919

Meat content and added water in meat products:

Dielectric spectroscopy

Hall et al., 1994

Detection of MRM:

Light microscopy SDS-PAGE Immunoassay

Pickering et al., 1995a Savage et al., 1995 Pickering et al., 199%

Determination frozen meat

Measurement of HADH activity

Gottesmann & Hamm, 1983; Billington et al., 1992

Species identification:

Immunoassay ELISA DNA probe

Yun et al., 1995 Patterson et al., 1983 Chikuni et al., 1990

of previously

Irridation of meat:

SDS-PAGE

Hassan, 1990

Ageing of meat:

SDS-PAGE

Wismer-Pedersen & Weber, 1987; Savage et al., 1996

Presence of offal:

ELISA

Patterson, 1985

TABLE 3 Working party on food authenticity

-_

Terms of Reference: (a>

To identify and advise on priorities in areas of food authenticity to be studied;

(bl

To consider what methods of analysis can be applied to detect adulteration misdescription, and advise on the significance of results;

(cl

To advise where work is needed to identify suitable methods to detect adulteration misdescription;

(d)

To monitor the Ministry’s programme on adulteration

(e)

To encourage industry and enforcement authorities to apply existing and new techniques, as appropriate, to ensure product authenticity.

and authenticity;

and and

and

should not be seen in isolation, but should link in with the industry’s own efforts in ensuring product authenticity. Also, it is important to realise that the Working Party does not replace existing enforcement activities nor the responsibilities of the local authorities. In order to be able to compare each authenticity issue on the same basis, the Working Party has developed a decision-tree based system (Fig. 1) to decide whether an issue warrants surveillance and, if so, what priority it should be given. Factors relevant to the authenticity issue are considered, as highlighted in the diagram, and a numerical scoring system is used to assess the particular problem and arrive at a priority rating. The question of whether suitable methodology exists to determine the authenticity of the product under investigation is considered by a Methodology sub-group, which is composed of technical experts. Where possible, the methods adopted will have been collaboratively tested, but this is not always essential for recommendation of a method. If no appropriate method exists then the sub-group advises on the need and practicality

K. D. Margin

of developing suitable methodology. This sub-group also has the important function of keeping abreast of any novel techniques which are being developed. Once the Working Party has agreed that an authenticity issue in a food product warrants a surveillance exercise, and the Methodology sub-group has recommended a method for such a purpose, then a surveillance exercise is organised. The benefit of such a formalised system is that once the results of the survey are known the enforcement authorities are in a stronger position to target their limited resources onto the real problems within food authenticity.

I C-r

Ye¶

Perception of Probkm?

fJ-0

Fig. 1. Decision tree process to determine the need for surveillance.

Authenticity issues

WHAT IS AUTHENTIC

S281

FOOD?

Before the different authenticity problems associated with meat and meat products are examined it is necessary to define what is “authentic”, or rather, “non-authentic” food. Within the UK this is defined as food which is not “of the nature or substance or quality demanded by the purchaser”. This can take many forms: (a) (i) Complete or partial omission or abstraction of valuable constituents. (b) (ii) Whole or partial substitution of food component with an undeclared alternative (usually cheaper). (c) (iii) Concealment of damage or inferior foodstuffs. (d) (iv) Adulteration: addition of undeclared substances or material so as to increase product bulk or weight or make the product appear better value than it is.

AUTHENTICITY

ISSUES

Figure 2 summarises the primary authenticity issues that are encountered with meat and fish products. This, of course, is not an exhaustive list and it is not within the scope of this paper to deal with anything other than an outline of the broad issues. Instances of accidental adulteration will not be covered. The “potential authenticity problems” have been divided into 4 broad categories purely for ease of discussion but in reality it is possible to have a mixture of 2 or more of these problems in a single product. Origin

(i) Geographic origin could include such problems as describing steak as Aberdeen Angus when it was not, or the passing off as ‘New Zealand’ some lamb that had originated from elsewhere. The prime purpose for doing so are economic gain where the described product commands a premium price compared with the product that is misrepresented. Unfortunately, there are no reliable tests available which will accurately determine the geographical origin, i.e. the country or region of origin, of meat samples. Techniques such as stable isotope ratio analysis by mass spectroscopy or site-specific natural isotope fractionation by nuclear magnetic resonance (SNIF-NMR), which have been used successfully for the determination of geographic origins of fruit juice and wines, would probably not be appropriate in the case of meats. Likewise, there is, as yet, no definitive test to differentiate between wild and farmed salmon though there are several parameters that can be measured which may help to increase the probability of correctly identifying wild from farmed salmon. The fat content of wild salmon is fairly consistent at about 9-12% (principally due to the fact that they are caught normally at a particular maturity and time in their life-cycle), while the fat content of farmed salmon is much more variable and ranges from about 7-8% up to 23% (Ackman & Takeuchi, 1986; Chanmugam et al., 1986; George & Bhopal, 1995; Nettleton & Exler, 1992; van Vliet 8z Katan, 1990). The type of fat within the salmon also differs, with the ratio of saturated: monounsaturated fat being higher in the farmed fish than the wild variety. Substitution

The section on substitution has been sub-divided into 3 main areas: (i) meat/fish protein, (ii) fat, (iii) other proteins. Obviously the issue here is one of deliberately misleading the

I

Fig. 2. Potential authenticity

I

MEAT/FISH PROTEIN

WILD/FARMED

AUTHENTICITY

PROBLEM

problems in meat and meat products.

FROZENfIXAWED

POTENTIAL

S283

Authenticity issues

consumer and there is no suggestion that these ingredients cannot be used legitimately with the proper lahelling. There are many different aspects to ‘substitution’ which can be considered but it is not possible within the constraints of this paper to deal with each sub-section and therefore only some aspects of meat protein substitution will he discussed. The determination of species is seen as important since some religious groups could meat. Other groups such as be offended by consuming “non-kosher” or “non-halal”

Comparison Country

TABLE 4 of Meat Definition Within Some European Countries

Animal carcase components specifically included in the meat definition

Austria: Belgium:

Hooves, claws, feathers, skin, eyes, uterus, testicles and tonsils. Blood, blood protein, bones (which are neither defatted or have muscle fragments removed). MRM, brains, rind, bone fragments, blood, blood protein, intestines (and fat associated with these), udders, tallow, blood and blood products.

Denmark:

Finland:

Animal carcase components specifically excluded from the meat dejinition

Blood, blood protein. Blood, blood protein.

France: Germany:

Skeletal muscles with fat attached, fat deposits in lymph nodes, muscles and connective tissue, tissue and pork salivary glands.

Blood, blood protein.

Greece:

Blood, blood protein, skin without cuticle and/or collagen, kidney, spleen and stomach.

Intestines, udders, lungs, pork skin with cuticle and oral mucous membrance.

Italy:

This requires clarification with the authorities on the acceptability of specific items.

Luxembourg:

Eyes, genital organs and foetal sac.

Netherlands:

Hooves, claws, pig skin.

Spain:

Natural proportions collagen and skin.

of fat, blood,

Sweden:

Blood, blood protein. MRM, connective tissue, brain, heart, lungs, intestines, tongue.

Switzerland:

Blood, fat, intestines.

UK:

Diaphragm, head meat, heart, liver kidney, pancreas, tail meat, tongue, thymus.

Brains, feet, intestine, testicles, udders, lungs, oesophagus, rectum, spinal cord, spleen, stomach, and Specified Bovine Offal.

S284

K. D. Hargin

vegetarians, vegans, pregnant women or people with particular allergies also need to know that the product they are buying contains exactly what is declared on the label, and nothing else. It should be realised that what is regarded as adulteration in one country may be perfectly acceptable in another. This is highlighted in Table 4 where it can be seen that even within EC Member States, because there is no harmonised definition of meat (for the purposes of compositional claims) there are differences in what can be claimed as ‘meat’. Components which may fall into this category are such things like blood plasma and MRM. Not only can this cause confusion among consumers but unfair competition may result if some manufacturers can claim a higher meat content for their products by using, e.g. blood plasma, than those in the countries where this is not permitted. Blood plasma is included often in meat products because of its excellent gellation and emulsification properties. Furthermore, since the addition of 2% blood plasma to a meat product can improve yield by 4-5%, and replace up to 10% lean meat content, the partial substitution of lean meat with blood plasma can offer great financial savings to the manufacturer. In the UK, although blood can be used in meat products, it cannot count towards the declared meat content but in the traditional analytical method (Stubbs & More, 1919) the nitrogen from the blood proteins would contribute to the total nitrogen content and thus lead to an elevated apparent meat content. Treatment The treatment of foodstuffs can take many different forms and not all are immediately obvious to the consumer. For example, the product may have been irradiated and not properly labelled. A joint of meat may have been previously frozen and passed off as ‘fresh’, i.e. not frozen. Fresh or chilled meat and poultry often command higher prices than their frozen counterparts. Dishonest traders therefore are provided with the opportunity to make improper financial gains by thawing frozen meat or poultry and presenting it for sale as chilled. It is an offence under UK food labelling regulations to sell previously frozen meat as chilled without an appropriate declaration to indicate that the meat has been previously frozen. The consumer has a basic right to know to what treatment any food has been subjected before it is purchased. Other issues Figure 2 lists a few ‘Other Issues’ which didn’t seem to fit neatly under the other headings. Briefly, these can include such instances where artificial colours are used and claimed as natural, the level of added water could be under-declared, or with the cooking method it might be claimed that a joint has been roasted when, in fact, it has been steamed. In essence, it remains that there are a variety of ways of misleading the consumer into buying something which he or she is not actually receiving. All the things that have been highlighted in Fig. 2 are real problems and need to be addressed in the interests of consumer protection. METHODS

OF ANALYSES

As analytical techniques developed throughout the 1800’s in response to the increasing instances of adulteration some inroads were made in the fight against the deceitful trader, although in the early days testing methods were often very crude. Authenticity testing and analytical techniques have improved immeasurably since then and must now draw on a

S285

Authenticity issues

wide variety of techniques and methods, each appropriate and specific to deal with a particular problem. Table 2 highlights some of the issues relevant to today’s market and the analytical techniques employed to verify the authenticity of meat products. The most appropriate technique for any particular sample will often be determined by the nature of the sample itself, e.g. whether it is raw or cooked, whole muscle or comminuted etc. However, it is important to remember that science has progressed to a very high degree in certain areas and that analysts and enforcement officers are often faced with judgements other than a straightforward interpretation of the scientific testing results. For example, most ELISA kits for meat speciation rely on detecting the soluble sarcoplasmic proteins from the particular meat species. Even minute traces of these proteins are sufficient to produce a positive reaction and at low levels of crosscontamination it is almost impossible to quantify these results with any real accuracy. Therefore, in a busy butcher’s shop where there is little time to strip down and clean a mincer every time a change of species is required should a butcher always be considered guilty of adulteration where an ELISA test indicates a species is present other than the declared one?

PREVIOUSLY

FROZEN

MEAT?

There are several methods which have been developed, both non-enzymic and enzymic (Abdallah, 1983; Chen et al., 1988; Jones & Dodd, 1993; Knight et al., 1985; Rehbein, 1979), which could be used to determine whether or not meat had been previously frozen. The one which has showed the most promise is the comparative measurement of b-hydroxyacyl-CoA dehydrogenase (HADH) activity in a sample before and following a freeze-thaw cycle (Gottesmann & Hamm, 1983). In common with other enzymic methods, the HADH method is based on the increased activity of the enzyme in the sarcoplasm resulting from the release of the enzyme from muscle mitochondria which have been damaged when the meat or poultry has been frozen and thawed. Increased HADH activity in juice expressed from a sample is an indication that the muscle has previously been frozen. This method has been used successfully to differentiate frozen-thawed meat from the equivalent fresh beef, veal, pork, mutton, poultry and game when the meat was frozen at -12°C or colder (Gottesmann & Hamm, 1983). A modification of the spectrometric techniques has been collaboratively tested by MAFF with respect to poultrymeat (Billington et al., 1992). The results of this trial indicated that the method as tested allows the differentiation of fresh and frozen-thawed chicken breast meat provided the freezing process has been undertaken at temperatures below -12°C. Samples pre-frozen at -6°C or chill-stored did not exhibit significantly different enzyme activities to fresh samples so the method cannot be used to differentiate such samples from fresh meat.

SPECIATION Several different techniques are currently used for the determination of species, primarily relying on detecting differences in proteins and are either electrophoretic or immunological methods (Barai et al., 1992; Patterson, 1985). One of the major drawbacks with such methods is that they do not perform well with heat treated samples. More recently DNA techniques have been applied to meat speciation with the advantage that the DNA is much more stable to cooking temperatures. Additionally, procedures like polymerase chain reaction (PCR) mean that the sensitivity of these tests are greatly enhanced and positive reactions are possible from the merest trace of the species under investigation.

S286

K. D. Hargin

Other techniques for the determination of species which have been used successfully on both raw and cooked meat products include DNA probes, and SDS-PAGE (Billett et al., 1996; Hitchcock & Crimes, 1985; McCormick et al., 1992; Zerifi et al., 1991).

WILD/FARMED

FISH

There have been many methods proposed to differentiate farmed from wild salmon, most based on the composition and content of fat (Cronin et al., 1991; Sylvia et al., 1995; Higgs et al., 1989). Work being carried out on mitochondrial DNA restriction fragment length polymorphism techniques to differentiate between species of salmon has also been investigated with the view to distinguishing wild from farmed salmon (Knox & Verspoor, 1991). However, there is not a great deal of difference at the DNA sequence level and, furthermore, the amount of fish that escape captivity and inter-breed with wild salmon would soon invalidate any observed differences. Pigmentation is the other factor which can be helpful in this detection process. Astaxanthine and canthaxanthin are two pigments commonly found in salmon. Wild salmon has a predominance of astaxanthine. By determining the ratios of the two pigments it should be possible to distinguish between the wild and fresh salmon. However, for some time now, canthaxanthin has been added to the feed of farmed fish in order to colour the flesh (astaxanthine is also added, but in smaller quantities since it is more expensive) therefore in practice this would not be a viable solution to the differentiation of wild from farmed salmon. One of the problems with the reliance on such factors is that in the farmed salmon these parameters can all be altered by manipulation of the fish’s diet. One possible solution in this case may be the separation and identification of the isomers of canthaxanthin and astaxanthine. There is only one isomer for natural astaxanthine, therefore if a robust and reliable system could be developed to differentiate the pigments’ isomers this could well form the basis of authenticating wild from farmed salmon (Schiedt et al., 1981). Thus at the present time, if a sample of salmon had a high level of total fat, a high ratio of saturated: monounsaturated fat and a high canthaxanthin level, then it is probably a farmed salmon. However, it would not be possible to definitely identify a sample as “wild” if it did not have high levels of these parameters. Within the UK and as part of MAFF’s authenticity programme much research has been conducted in recent years into the development of methods to detect both MRM and blood plasma in meat products.

MECHANICALLY

RECOVERED

MEAT (MRM)

One of the main problems in trying to detect MRM in meat products is that MRM itself is a generic term covering a wide range of product compositions (Crosland et al., 1995; Meech & Kirk, 1986). The work by Crosland et al. (1995) compared hand-deboned meats to MRM from various different sources and species, and prepared using a variety of machines and processing conditions. In general, the calcium and iron levels were higher, the collagen level lower, and in red meat MRM the total purines were higher, in the MRM samples compared with the hand-deboned meats. However, the degree of variation found in the composition of the starting materials and from the operating conditions or machine type used make it impossible to exploit composition as a positive means of identifying MRM in meat products.

Authenticity issues

S287

Although no obvious marker compound has been identified in MRM, work by Savage et al. (1995) has shown that significant differences do exist in the electrophoretic patterns of extracts from MRM and corresponding hand-deboned meat. Using this technique it is possible to identify MRM in raw meat mixtures down to a level of 5% MRM for beef and pork, but only to lo-15% for poultrymeat MRM. The technique was inconclusive when applied to cooked and canned samples. A degree of quantification may be possible with this method by densitometric scanning of the gels although this had not been tried. An immunological procedure has also been tried in which antibodies were raised to chicken bone marrow proteins which showed a strong reactivity with chicken and turkey MRM extracts but showed little reaction with extracts of MRM and hand-deboned meat of the common meat species (Pickering et al., 19956). However, the antisera raised showed cross-reactivity with blood, skin and soya protein at levels which affect the accuracy of the developed ELISA. When applied to raw commercial meat product samples the technique showed promise in being able to qualitatively indicate the presence of MRM. The antisera did not respond to cooked chicken MRM or heat processed samples. Of other analytical techniques which have been tried the two most promising would appear to be microscopy (Pickering et al., 1995b) and electrophoresis of cyanogen bromide peptides. In the microscopy study hyaline cartilage, a dense connective tissue normally located within bones, was investigated as a potential marker for the presence of MRM in meat products. Hyaline cartilage was identified in most samples of MRM examined and was generally found in large amounts, however it was more difficult to detect it in MRM and hand deboned meat mixtures and quantification was not possible. The cartilage was observed in some commercially canned meats examined and thus the approach may have some value as a rapid screening technique. Cyanogen bromide, a reagent which specifically cleaves proteins at methionine residues, previously has been used to identify canned fish species by iso-electric focusing of the solubilised protein fragments. A similar approach had been tried with cooked chicken MRM to enable its differentiation from hand deboned chicken. However, it has been discovered that it is not the solubilised protein fragments that held the distinguishing characteristics, but the core peptides, the hydrophobic centres of the original proteins, which precipitate after dialysis of the cyanogen bromide digest. The core peptides are washed in a mild protein solubilising reagent before final cleavage with the enzyme pepsin. This final digest is then fractionated by SDS electrophoresis and visualised by silver staining. It has been suggested that a characteristic protein band of between 20-29KDa is present exclusively in raw and cooked chicken MRM under these extraction conditions.

BLOOD PLASMA Research commissioned by MAFF in the UK examined both an immunodiffusion and an ELISA technique in an attempt to overcome the problem of identification of blood plasma in meat products (Church & Hart, 1995; Price et al., 1992). An immuno double diffusion in agar-gel approach was only partially successful with the limit of detection at 8% for the cooked beef antibody and 1% for the raw pork antibody. The raw pork antibody was unsuitable for use with heat treated products. The ELISA protocol that has been developed shows more promise and appears capable of detecting added blood plasma at low levels of addition (cu. 0.2% m/m as dried plasma) in a variety of both raw and cooked meat products. However, at present the test is unable to identify species origin of the plasma though this is not considered a serious drawback, especially if the technique is to be used for screening purposes. In terms of labelling

S288

K. D. Hargin

requirements and checking the authenticity of a product, a ‘positive-negative’ result for the presence of blood plasma may be all that is required.

CHEMOMETRICS Since foodstuffs exhibit a large natural variation due to such factors as species, breed, growing environment, maturity at slaughter, etc. and many different techniques are employed to examine specific parameters, analysis and comparison of the data from different sources can be extremely complex. The difference between an “authentic” and a “non-authentic” sample can often be so subtle that computer-based statistical programs are required to determine which of the various parameters are most significant in the determination of the regression. It is not within the scope of this paper to discuss the various statistical techniques available, suffice to say that care should be taken when using chemometrics to ensure that whatever technique is employed is appropriate and does not in itself introduce untoward bias in the final results.

CONCLUSION Each country will have specific concerns and will wish to determine its own particular priorities for targeting authenticity issues. However, it has to be recognised that determining the authenticity of a product can be complex, particularly if legal action is to be considered. As meat products become more intricate, scientists will have to work harder and maintain a high degree of innovativeness in order to keep apace with the efforts of the unscrupulous to cheat consumers. Many novel and diverse approaches may have to be examined before a suitable method can be developed. The consumer is the final link in the food chain, and without question the most important one. Therefore any product no matter how good it claims to be, or how technologically advanced the processing must not put at risk in any way or mislead the consumer. Protecting the consumer by providing the necessary information on product labels to enable an informed decision and by ensuring that the product is exactly what it purports to be, therefore, must be seen by both manufacturers and enforcement authorities as paramount to serving the consumer.

REFERENCES Abdallah, N. M. (1983). Journal of the Egyptian Vet. Med. Association, 43, 383. Ackman, R. G. & Takeuchi, T. (1986). Lipids, 21, 117. Barai, B. K., Nayak, R. R., Singhal, R. S. & Kulkarni,

P. R. (1992). Trends in Food Science and

Technology, 3, 69.

Billett, E. E., Bevan, B., Pickering, K. & Gibbons, B. (1996). J. Sci. Food Agric., 70, 396. Billington, M., Bowie, H., Scatter, S., Walker, H. &Wood, R. (1992). J. Assoc. Publ. Analysts, 28, 103. Chanmugam, P., Boudreau, M. & Hwang, D. H. (1986). J. Food Sci., 51, 1556. Chen, M., Yang, W. & Guo, S. (1988). Meat Science, 24, 223. Chikuni, K., Ozutsumi, K., Koishikawa, T. & Kato, S. (1990). Meat Sci., 27, 119. Church, P.N. & Hart, R.J. (1995), Detection of added blood plasma in meat products part II, MAFF project No. AN0623. Cronin, D. A., Powell, R. & Gormley, R. (1991). Ir. J. Food Sci. and Technol., 15, 53. Crosland, A. R., Patterson, R. L. S., Higman, R. C., Stewart, C. A. & Hargin, K. D. (1995). Meat Sci., 40, 289.

Authenticity issues

S289

George, R. & Bhopal, R. (1995). B. Food., 97, 19. Gottesmann, P. & Hamm, R. (1983). Fleischwirtsch., 63, 219. Hall, M., Li, Z. & Gabriel, C. (1994). Spectrocopic investigation of the dielectric properties of some foods andfood components. MAFF Publications, London. Hassall, A. H. (1855). The Lancet, 1406 e 5. Hassall, A. H. (1857). The Lancet, 1406 e 4. Hassall, A. H. (1876). The Lancet, 2025 c. Hassan, I. M. (1990). Food Chem., 35, 263. Higgs, D. A., Skura, B. J., Dosanjh, B. H., Yan, D., Powrie, W. D. & Donaldson, E. M. (1989). Can. Aquaculture, 5, 5 1. Hitchcock, C. H. S. & Crimes, A. A. (1985). Meat Sci., 15, 215. Jones, M. & Dodd, E. R. (1993). MAFF Project No. N1917. Knight, M. K., Church, P. N. & Wood, J. M. (1985). BFMZRA Technical Note No. 21. Knox, D. & Verspoor, E. (1991). Aquaculture, 98, 249. McCormick, R. J., Collins, D. A., Field, R. A. & Moore, T. D. (1992). J. Food Sci., 57, 516. Meech, M. V. & Kirk, R. S. (1986). J. Assoc. Publ. Analysts, 24, 13. Nettleton, J. A. KcExler, J. (1992). J. Food Sci., 57, 257. Patterson, R. L. S. (ed.) (1985). Biochemical Zdenttjication of Meat Species. Elsevier Applied Science Publishers, London. Patterson, R. L. S., Jones, S. J. & Kang’ethe, E. K. (1983). Proceedings of the European Meeting of Meat Research Workers, No. 29, Vol. II, E.7, 657. Pickering, K., Evans, C. L., Hargin, K. D. & Stewart, C. A. (1995). Meat Sci., 40, 319. Pickering, K., Griffin, M., Smethurst, P., Hargin, K. D. & Stewart, C. A. (1995). Meat Sci., 40, 327. Price, K.R., Hart, R.J. & Church, P.N. (1992). Detection of added bloodplasma in meat products part I. MAFF project No. N2328. Rehbein, H. (1979). Z. Llebensm. Unters. Forsch., 169, 263. Savage, A. W. J., Richardson, R. I., Jolley, P. D., Hargin, K. D. & Stewart, C. A. (1995). Meat Sci., 40, 303.

Savage, A. W. J., Vallis, L., Wood, J. D. & Warkup, C. C. (1996). Post-mortem proteolysis assessed by SDS-PAGE as a predictor of meat tenderness. Submitted to Meat Sci. Schiedt, K., Leuenberger, F. J. & Vecchi, M. (1981). Helvetica Chimica Acta, 64,449. Stubbs, G. & More, A. (1919). Analyst, 44, 125. Sylvia, G., Morrissey, M. T., Graham, T. & Garcia, S. (1995). J. Aquat. Food Product Technol., 4, 51.

van Vliet, T. & Katan, M. B. (1990). Am. J. Clin. Nutr., 51, 1. Wismer-Pedersen, J. KcWeber, A. (1987). Fleischwirtsch., 67, 351. Yun, H. P., Woodward, B. B. & Shiow, H. H. (1995). J. Food Protect., 58, 555. Zerifi, A., Labie, C. & Benard, G. (1991). Fleischwirtsch., 71, 1060.