Polycyclic aromatic hydrocarbons in grilled meat products—A review

Food Chemistry 10 (1983) 129-139

Polycyclic Aromatic Hydrocarbons in Grilled Meat Products A Review Kristen Fretheim* Norwegian Food Research Institute, P.O. Box 50, N-1432 Aas-NLH, Norway (Received: 25 January, 1982) ABSTRACT Current efforts to detect and quantify carcinogenic polycyclic aromatic hydrocarbons (PAH) in the environment include analyses of foods. Grilledfoods have been under scrutiny for almost 20 years. In this review reports concerning PAH contamination of grilled meat products are discussed. It is evident that the level of contamination varies considerably, primarily due to the extent of fat pyrolysis which has taken place. If proper precautions against fat pyrolysis are taken, and out-of-theordinary fuels such as crumpled paper or cones are not used, the PAH contamination is reduced substantially. Furthermore, if the relatively low consumption of grilled meat products is taken into consideration public concern over possible health risks due to grilling appears unwarranted.

INTRODUCTION The carcinogenicity and ubiquity, at very low concentrations, of polycyclic aromatic hydrocarbons (PAH) have made these substances a challenge to analytical chemists. A great number of such c o m p o u n d s have been identified and quantified in virtually all segments of our environment; the literature on P A H in foods has been reviewed by Lo & Sandi (1978). Seppilli & Scassellati Sforzolini (1963) were the first to detect carcinogenic PAH's in grilled meat. * Present address: Food Research Laboratory, P.O. Box 52, North Ryde, New South Wales 2113, Australia. 129 Food Chemistry 0308-8146/83/0010-0129/$03.00 © Applied Science Publishers Ltd, England, 1983. Printed in Great Britain

TABLE

1

r30 ~, 20 ~85

19

2"3

1:0.2:1.9: - -

1:0.9:1.0:1 '5 1:0.8:0.4:0.8

1.2 10-1

0.8 4.6

0.7 9.9

0.3

1:0-8:2.0:-1: 1.2:1-6: 1:2.5:10:5"0

1: - - :0.3: - 1:1.7:1.3:-1:l.5:2-5:-1:--:0.4:-1: - - : 0.4: - -

1:0.9: - - : - -

(60 40 0.6

f39 el, 50 (~

1:-- :3.5:-

13"3

(25 30 0"15

f50 ~ 30

1.0-8-0 ND ND

I:II:IlI:IV

Number of samples

3

1 1

Products

GLC, flame ionisation HPLC GLC HPLC GLC

HPLC, uv and/or fluorescence spectroscopy

TLC, fluorescence spectroscopy

TLC, ultraviolet and fluorescence spectroscopy

Fritz (1973)

T6th & Blaas (1973)

Panalaks (1976)

Doremire et aL (1979)

Capillary GLC, mass fragmentography Binnemann (1979)

Reference

in C h a r c o a l G r i l l e d M e a t

Analytical method z

(PAH)

1HPLC GLC 2 TLC, in situ fluorescence spectroscopy 1

1 1

1

6 6 6 6 ? I 1

Chrysene IV

21-5 29.3 10.5 ND 3 0-2~0 5.0 0-5

B(a)A 1 111

4

B(b)F a 11

<0.5

B(a)P L I

~30 Chinese sausages 25 Sausages 0.06 ('Kulmbacher Bratwurst') Sausages 15.2 ('Coburger Bratwurst') Roast beef 0"8 Bacon, fat 12-6 ('Schweinebauch') Sausages 10 ('Thiiringer Bratwurst')

Frankfurters

Hamburger

Steak

Sausages ('Rostbratwiirsten') Beef Pork Lamb Turkey Steak Pork chops Chicken

Sample

(/~g/kg)

Mean Concentrations R e p o r t e d f o r C a r c i n o g e n i c P o l y c y c l i c A r o m a t i c H y d r o c a r b o n s

~"

~

< 0.2 <0.2 <0.1 < 0.2

5.8 8

2.6 ND 11.2 7.9 3.7 I 1.1 50.4 10.5

7 4.2 0.7 10.7 9.5

1-3

<5 <4 <3 <2

1.4 4.5

2"7 ND 4.5 8.2 3"2 10-3 31"0 3-6

11 8.7 3.3 17.7

Abbreviations for PAH's: B(a) P = Benzo(a)pyrene. B(b)F = Benzo(b)fluoranthene. B(a)A = Benz(a)anthracene. Formulae and relative carcinogenicities are given in Fig. 1. 2 Abbreviations for analytical methods: GLC = Gas liquid chromatography. TLC = Thin layer chromatography. HPLC = High performance liquid chromatography. PC = Paper chromatography. 3 ND = Not detected. Blank spaces imply not investigated.

Pork chops Pork 'bones' ('fleskebein') Beefsteak on the bone Lamb cutlets

Steak Steak

Pork steak ('Schweineriicken') Fat Lean Roast beef Sausages ('Coburger Bratwurst') Hamburger, fat Hamburger, lean Hamburger, frozen Pork chop Chicken Sirloin steak T-bone steak Ribs 0"6 1.4

1"7 ND 3"2 6"3 2"2 9'3 25"4 2'2 1:--:0.2:0.1 1 : :0.6:0.2

1:

1:

:0"4:0"3 : 1"0:0'8 1: :0-9:0.6 1 : - - :0-9:0-8 1: - - :0"6:0'5 1:--:0"3:0"2

1:--:1"0:0-7

1:0"2:1.6: 1:--:2"1: 1:--:4"7: 1:0"9:1'7:

HPLC, ultraviolet and fluorescence spectroscopy

PC, ultraviolet and fluorescence spectroscopy

PC, ultraviolet spectroscopy

Lijinsky & Shubik (1964) Fretheim (unpublished results)

Lijinsky & Shubik (1965)

Lijinsky & Ross (1967)

F/tbifin (1968)

U~

eb

2'

132

Kristen Fretheim

This review restricts itself to the contamination of grilled meat products by PAH for two reasons: (1) Grilling of foods is increasing in many countries, including Norway, and it is felt appropriate to collect available information on possible ill effects from grilling. (2) It has been reported that the levels of contamination by these compounds in grilled products can be influenced both by the type of raw material used and by the procedure and/or the apparatus employed. In addition to bringing together the available data it is the aim of this review to evaluate whether the situation calls for some kind of action by regulatory agencies.

ANALYTICAL DATA Table 1 summarises the analytical results reported for meat products grilled over charcoal. It can be seen that, with few exceptions, the researchers have, broadly speaking, established similar relative proportions between the PAH's of the various samples, whereas the respective levels determined differ significantly. The assertion that the absolute concentration of PAH is, in general, subject to greater variations than the relative concentration of the individual compounds (T6th & Blaas, 1973) is, therefore, supported. It should be realised, however, that the observed differences in concentration levels may stem both from actual differences in the products analysed and from lesser or greater systematic errors or shortcomings of the analytical procedures employed. A brief evaluation of the various methods in question is, therefore, called for here.

ANALYTICAL PROCEDURES The analysis of PAH is constantly being improved, the latest contribution with regard to foods being the paper by Crosby et al. (1981). The following review is limited to methodology employed in work quoted in Table 1.

P A H in grilled meat products

133

Clean-up By and large all the cited researchers have employed similar steps in their procedures for obtaining a final solution of purified PAH, liquid-liquid extraction and column chromatography being the essential steps employed. There are differences, however, both in choice of solvents and chromatographic materials, as well as in whether or not the meat samples are hydrolysed in an initial step. The importance of these differences can only be evaluated in terms of figures on recovery. Early workers (Lijinsky & Shubik, 1964, 1965; Lijinsky & Ross, 1967; Ffibifin, 1968) did not provide recovery data, but Lijinsky & Shubik (1964) comment that, due to losses, the concentrations they report are minimum values. Fritz (1973) reported about 80 ~ recovery of B(a)P (abbreviations are explained in the footnotes to Table 1) whilst Grimmer & Hildebrandt (1967) (whose method was employed by T6th & Blaas (1973)) obtained recoveries ranging from 87 ~ to 98 ~ for the PAH's listed in Table 1. In my own work, using the polycarbonate extraction procedure of Potthast & Eigner (1975), recoveries were estimated to be about 80 ~ (unpublished results). Panalaks (1976) and Binnemann (1979) hydrolysed their samples prior to extraction. By employing internal standards they obtained average recoveries of 104 ~ and 105 ~ , respectively, in their determinations of B(a)P. Doremire et al. (1979) did not report on recoveries obtained. In summary, recovery does not appear to be a cause for serious concern when evaluating reported PAH concentrations. It must be pointed out, however, that, except for the two workers who employed an initial step of hydrolysis (Panalaks, 1976; Binnemann, 1979), the reported recoveries do not include losses due to incomplete extraction from the solid meat samples. Nevertheless, the data quoted in Table 1 do not suggest that this difference in clean-up has had any major effect on the PAH levels determined.

Separation and determination There can be no doubt that capillary gas-liquid chromatography-mass fragmentography (GC-MF) is the method of choice for the determination of known carcinogenic PAH's. As pointed out by Binnemann (1979), the reproducibility, specificity and sensitivity of this method makes it preferable. The other methods are innately inferior in terms of

134

Kristen Fretheim

separation power, and if separation is incomplete and subsequent determination insufficiently specific, the resulting values may be too high. Particularly if checks on recovery have not been included, reports on surprisingly high concentrations must be viewed with some scepticism. Panalaks (1976) provided a comparison of the accuracy of HPLC and GLC (not capillary) in these analyses by subjecting his PAH extracts to determination by both methods (Table 1). Values obtained for low concentrations differ by up to 50 % but his results suggest that, within this range, reported values are accurate.

EVALUATION OF R E P O R T E D PAH CONCENTRATIONS Table 1 indicates that the level of PAH contamination may vary from undetectable amounts to maximum values in the order of 50 #g/kg in the case of B(a)P. The high value of 50-4/~g/kg reported by Lijinsky & Ross (1967), is not supported by data on recovery and represents one sample only. However, other analyses in the same investigation yielded much lower values, indicating that the levels were, in fact, very different. Similarly, Panalaks (1976) found relatively high concentrations in two of his samples and low concentrations in others, in his case supported by checks on recovery. It appears, therefore, that the wide range of concentrations reported do reflect real differences in levels of contamination, and the question arises: What are the reasons for these differences?

FACTORS I N F L U E N C I N G THE LEVEL OF CONTAMINATION Effect of the sample's fat content

As early as 1964, Lijinsky and Shubik stated: 'The most likely source of the polynuclear hydrocarbons is the melted fat which drips on the hot coals and is pyrolysed at the prevailing high temperature. The polynuclear hydrocarbons in the smoke are then deposited on the meat as the smoke rises'. This statement was based on their observation that no nitrogen-containing polycyclic compounds could be detected in extracts of the grilled meats whereas carbazoles and acridines are very much in

P A H in grilled meat products

135

evidence in pyrolysates of nitrogen-containing raw materials. Lijinsky & Shubik (1965) determined the contamination of both lean meat (steak) and fat meat (ribs) as a result of charcoal grilling (Table 1). The increased PAH levels of grilled ribs were taken as support of the above fat pyrolysis hypothesis. Subsequent work by Lijinsky & Ross (1967), Fritz (1973), T6th & Blaas (1973), and Doremire et al. (1979; see Table 2) has provided further support, so there can be no doubt that fatty meats yield grilled products with higher levels of PAH contamination than lean meats. TABLE 2 Effect of Fat Content (Adjusted) on the Benzo(a)pyrene Content of Charcoal Grilled Ground Beef Patties (Mean value of six determinations (Doremire et al., 1979))

Percentage fat Benzo(a)pyrene conc. (~g/kg)

15.0 16.0

19.5 22.8

29.8 30'9

39.1 121-0

Effect of variations in the grilling process

Masuda et al. (1966) grilled fish in an electric broiler and found only minimal amounts of PAH to be produced; a gas grill yielded somewhat higher levels. Investigations by Lijinsky & Ross (1967) showed that the more severe the heat treatment (extended exposure, closeness to heat source), the higher the resulting concentrations of PAH. If dripping of melted fat onto the heat source was prevented, as in electric grilling or in other grills of appropriate design, no carcinogenic PAH's were detected in the grilled products. The latter prerequisites for attaining minimal PAH levels have been confirmed by other workers (Grimmer & Hildebrandt, 1967; T6th & Blaas, 1973; Lintas & De Matthaeis, 1979). Thus, it has been indisputably demonstrated that the grilling procedure has a definite influence on the extent to which grilled products are contaminated by PAH. Effect of various fuels

Ffibifin (1968),. Fritz (1973), T6th & Blaas (1973), and Binnemann (1979) have investigated the effect on contamination of grilling over fuels other than charcoal. The unambiguous conclusion to be drawn from their work is that charcoal is preferable; hardwood and crumpled paper, as well as

136

Kristen Fretheim

pine or fir cones, all lead to increased levels of PAH contamination. As pointed out by T6th & Blaas (1973), the difference probably arises from the fact that, whereas charcoal smoulders with hardly any emittance of smoke, the other fuels produce more or less sooty smoke. PAH's from the smoke are assumed to settle on the goods being grilled.

TOXICOLOGICAL E V A L U A T I O N OF THE PAH CONTAMINATION Generally speaking, the severity of any toxic contamination arises from the toxicity, as well as the concentration, of the contaminating compounds. PAH toxicity rests with the acknowledged potency of some PAH's as carcinogens (Fig. 1) and will not be commented on further here. The question is whether or not the concentrations reported in Table 1 constitute a cause for alarm. To the author's knowledge the only well defined guideline for answering that question is provided by the West German meat regulations which state that the edible portion of smoked meat products shall contain no more than 1 #g/kg of B(a)P. By this standard most of the products in Table 1 are unfit for human consumption. It must be realised, however, that this West German

Benzo [a]pyrene

Benzo[b]fluoranthene

++-t-

++

Benz[a]anthracene +

Chrysene

+ Fig. 1. Structural formulae and relative carcinogenicities of polycyclic aromatic hydrocarbonsincludedin Table 1. + Uncertainor weaklycarcinogenic. + Carcinogenic. + +, + + + Strongly carcinogenic.(Committeeon Biologic Effects, 1972; cf. IARC Working Group on the Evaluationof the CarcinogenicRisk of Chemicalsto Man, 1973).

P A H in grilled meat products

137

regulation is more or less arbitrary. It was found that proper processing procedures yielded smoked products containing less than 1/~g/kg of B(a)P (T6th & Blaas, 1972), so this limit was introduced to rid the market of black-smoked products containing high levels (up to 55 #g/kg) of B(a)P. The latter products were deemed undesirable since their relatively high PAH content was suspected to be capable of possibly having ill effects on the health of consumers. Nevertheless, as pointed out by Lo & Sandi (1978), there is no evidence that any PAH compound can cause cancer in man via the oral route, especially not at the concentrations in question. Another point is the relative importance of grilled products as compared with other foodstuffs. Data by Fritz (1971), based on analyses and consumption patterns in East Germany, place PAH intake due to eating of grilled foods at about 0-25 ~ of the total. Undoubtedly, grilling is much more common in, for example, the USA, but even a twenty-fold relative increase only brings grilled food PAH up to 1/20 of the total. This evidence that the PAH intake from grilled foods is a minor problem is supported by the conclusions drawn by Grimmer & Hildebrandt (1967), among others. There is, however, a different aspect of the issue to be considered. Elmenhorst & Dontenwill (1967) found that grilling of 1 kg of bacon produced smoke containing 1.29 mg B(a)P, as well as other PAH's. To what extent does such smoke contaminate the atmosphere for people working at commercial grills ?

CONCLUSIONS Analytical works over the past decade have substantiated the early findings of Lijinsky and his coworkers (1964, 1965, 1967): PAH contamination of grilled foods is primarily due to pyrolysis of melted fat; practical measures that bring about a reduction in fat pyrolysis reduce PAH concentrations to very low levels. The possibilities include limiting grilling to lean meat, avoiding excessive heating, or keeping melted fat away from the source of heat. Thus, electric grilling is preferable as far as PAH is concerned. Furthermore, German workers have shown that solid fuels other than charcoal are unsuitable due to the PAH content of the smoke they produce. It appears that no more research is needed to support Lijinsky's

138

Kristen Fretheim

original conclusions or to determine the general level of contamination caused by grilling over charcoal. The remaining issue is one for governmental authorities. Are traces o f P A H in charcoal grilled foods a reason for concern? The present author suspects not. On the other hand, however, a ban on (commercial) grill designs that do not prevent fat pyrolysis is conceivable.

REFERENCES Binnemann, P. H. (1979). Benz(a)pyren in Fleischerzeugnissen, Z. Lebensm. Unters.-Forsch., 169, 447-52. Committee on Biologic Effects of Atmospheric Pollutants (1972). Particulate polycyclic organic matter, Washington, DC, National Academy of Sciences. Crosby, N. T., Hunt, D. C., Philip, L. A. & Patel, I. (1981). Determination of polynuclear aromatic hydrocarbons in food, water and smoke using highperformance liquid chromatography, Analyst, 106, 135-45. Doremire, M. E., Harmon, G. E. & Pratt, D. E. (1979). 3,4-Benzopyrene in charcoal grilled meats, J. Food Sci., 44, 622-3. Elmenhorst, H. & Dontenwill, W. (1967). Nachweis cancerogener Kohlenwasserstoffe im Rauch beim Grillen fiber Holzkohlenfeuer, Z. Krebsforsch., 70, 157-60. F/tbi/m, B. (1968). Kanzerogene Substanzen in Speisefett und-51, Arch. Hyg., 152, 251-4. Fritz, W. (1971). 12. Umfang und Quellen der Kontamination unserer Lebensmittel mit Krebserzeugenden Kohlenwasserstoffen, Erndhrungsforsch., 16, 547-57. Fritz, W. (1973). Zur Bildung cancerogener Kohlenwasserstoffe bei der thermischen Behandlung von Lebensmitteln, 5, Dtsch. Lebensm.-Rdsch., 69, 119-22. Grimmer, G. & Hildebrandt, A. (1967). Kohlenwasserstoffe in der Umgebung des Menschen, V, Z. Krebsforsch., 69, 223-9. IARC Working Group on the Evaluation of the Carcinogenic Risk of Chemicals to Man (1973). Certain polycyclic aromatic hydrocarbons and heterocyclic compounds. Vol. 3. Lyon, International Agency for Research on Cancer. Lijinsky, W. & Ross, A. E. (1967). Production of carcinogenic polynuclear hydrocarbons in the cooking of food, Fd. Cosmet. Toxicol., 5, 343-7. Lijinsky, W. & Shubik, P. (1964). Benzo(a)pyrene and other polynuclear hydrocarbons in charcoal-broiled meat, Science, 145, 53-5. Lijinsky, W. & Shubik, P. (1965). Polynuclear hydrocarbon carcinogens in cooked meat and smoked food, Ind. Med. Surg., 34, 152-4. Lintas, C. & De Matthaeis, M. C. (1979). Determination of benzo(a)pyrene in smoked, cooked and toasted food products, Fd. Cosmet. ToxicoL, 17, 325-8.

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Lo, M.-T. & Sandi, E. (1978). Polycyclic aromatic hydrocarbons (polynuclears) in foods. In: Residue reviews (Gunther, F.A. (Ed.)), 69, 35-86. Masuda, Y., Mori, K. & Kuratsune, M. (1966). Polycyclic aromatic hydrocarbons in common Japanese foods. I, GANN, 57, 133-42. Panalaks, T. (1976). Determination and identification of polycyclic aromatic hydrocarbons in smoked and charcoal-broiled food products by high pressure liquid chromatography and gas chromatography, J. Environ. Sci. Health, Bll, 299-315. Potthast, K. & Eigner, G. (1975). A new method for the rapid isolation of polycyclic aromatic hydrocarbons from smoked meat products, J. Chromatogr., 103, 173-6. Seppilli, A. & Scassellati Sforzolini, G. (1963). Sulla presenza di idrocarburi policiclici cancerigeni nelle carni cotte alia graticola, Boll. Soc. Ital. Biol. Sper., 39, 110-12. T6th, L. & Blaas, W. (1972). Einfluss der R/iuchertechnologie aufden Gehalt von ger~iucherten Fleischwaren an cancerogenen Kohlenwasserstoffen, I. Fleischwirtsch., 52, 1121-4. T6th, L. & Blaas, W. (1973). Der Gehalt gegrillter Fleischerzeugnisse an cancerogenen Kohlenwasserstoffen, Fleischwirtsch., 53, 1456-9.