Quality of Raw Minced Beef

Quality of Raw Minced BeefAuthor(s): Michele C. Daly, P. A. Morrissey and D. J. BuckleySource: Irish Journal of Agricultural Research, Vol. 15, No. 3 (Dec., 1976), pp. 283-289Published by: TEAGASC-Agriculture and Food Development AuthorityStable URL: http://www.jstor.org/stable/25555830 .

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Ir. J. agric. Res. 15: 283-289, 1976

QUALITY OF RAW MINCED BEEF

Michele C. Daly and P. A. Morrissey

Department of Dairy and Food Chemistry, University College, Cork

D. J. Buckley

Department of Dairy and Food Technology, University College, Cork

ABSTRACT

A survey of the quality of minced beef, randomly sampled at retail outlets in Cork City, was carried out during the first 8 months of 1975. The samples were assayed for total aerobic count, coliform, coagulase-positive staphylococci, pH, extract release volume, total volatile nitrogen and tyrosine value. The total aerobic plate count ranged from a low of 3.5 x 105/g to a high of 1.3 x 109/g. Coagulase-positive staphylococci were found in 10 out of 16 samples examined: the counts ranged from 1.0 x 102 to 2.5 x 103 coagulase-positive staphylococci/g. All the samples examined were coliform positive and the counts on violet red bile ranged from 1.9 X 103/g to 5.3 X lOtyg.

Results of the various chemical and physico-chemical tests used to assess freshness are presented and discussed.

INTRODUCTION

Spoilage of meat has been defined as the "development of undesirable organoleptic characteristics in or on meat" (1). Although it is easy to detect spoilage in the advanced

stages, detection of the initial or onset stages still remains controversial and unsatis

factory. Any procedure which is to be used as a spoilage indicator should satisfy the

following criteria: a) recognise the initial stages of spoilage; b) reduce public health

hazards; c) be technically feasible; d) be administratively feasible; e) give an idea of

expected shelf-life. The shelf-life and stability of uncooked meats, particularly minced or ground meats, are influenced considerably by the initial and contaminating micro

organisms. All the reported studies on the quality of refrigerated minced beef are

based on bacteriological analyses (2, 3, 4, 5, 6). Some authors have suggested sanitary standards based on bacterial numbers

(7, 8, 9) while others have considered the type as well as the number of micro

organisms when proposing standards (10). The suggested standards for total viable counts in minced beef have varied from 0.25 to 10 million per gram and the suggested

283



284 IRISH JOURNAL OF AGRICULTURAL RESEARCH, VOL. 15, NO. 3,1976

coliform standards have ranged from zero to 200 per gram. In Oregon (8) meat is deemed to be adulterated if the total viable count and coliform count exceed 10 million per gram and 50 per gram respectively. In Massachusetts (11) the aerobic

plate count per gram limit is 100,000 and the coliform limit is 100, while in Rhode Island (11) the guidelines are IO6 per gram for the aerobic plate count and 100 per gram for coliform. Recently the Canadian Federal Health Protection Branch (12) proposed mandatory microbial standards for minced meat of 107 per gram for total aerobic count and 100 per gram for coliform. The enumeration of bacterial numbers has been considered to be impractical and time consuming by a number of workers, and various chemical and physico-chemical tests for meat spoilage have been pro

posed. These methods have been reviewed by Dainty (1) and Pearson (13). For the purpose of routine quality control, Pearson (14) has proposed a number

of cut-off values to assess acceptability. However, he did not include any bacterial counts in his report, the absence of which makes it difficult to determine the usefulness of the chemical and physico-chemical methods for routine quality control. The need for such information prompted the study reported here. In addition there is at present considerable interest within the European Economic Community to establish legis lation for uniform methods of testing and official standards for food products to facilitate trade in the Community (15). The second objective of the present study was to obtain information on the quality of minced beef at retail outlets which may be of use in establishing quality standards.

EXPERIMENTAL

Minced meat samples Minced meat samples (250 to 400g) were purchased at retail outlets in Cork City

during the first 8 months of 1975 and immediately transported to the laboratory for

testing. Each store was sampled at about 2-monthly intervals, giving a total of 29

samples.

Bacteriological analyses Five-gram samples were aseptically weighed into sterile jars containing 45 ml

sterile ^-strength Ringer's solution for the micro-biological tests. The samples plus diluent were placed in a sterile plastic bag and blended for 2 min in a Colworth Stomacher 400. Total aerobic counts were made using Tryptone Glucose Extract Agar

(TGE) and the conventional spread plate technique (16). The plates were incubated at 30?C for 3 days.

The coliform count was determined using the poured plate technique with boiled violet red bile agar (VRB). On solidification, a thin overlay was applied and the plates

were incubated at 37?C for 24 hours. In addition, samples were inoculated into tubes



DALY ET AL: MINCED BEEF 285

of MacConkey broth. The tubes were incubated at 37?C for 2 days and examined for

the presence of acid and gas. The presence of Escherichia coli or Enterobacter aero

geneSy or both, was also determined by streaking samples producing acid and gas on

Eosin Methylene Blue Agar (EMB). The plates were incubated at 37?C for 2 days. The coagulase-positive Staphylococcus was determined using the spread date

technique on Baird-Parker medium (17) and the plates were incubated at 37?C for 24

hours. Suspicious colonies were then transferred to Brain Heart Infusion (BHI) broth

and incubated for 18 hours at 37?C. A coagulase test was then performed on these

cultures using the tube technique (18). Staphylococcus aureus A was used as a positive control and Streptococcus lactis as a negative control.

Chemical analyses Extract release volume (ERV) was determined by the method of Jay (19) as modi

fied by Pearson (14). Tyrosine value was determined according to the procedure of Pearson (14). The tissue was homogenised in 5% trichloroacetic acid for 2 min in a

Colworth Stomacher 400. Total volatile nitrogen (TVN) was determined by the macro

Kjeldahl method of Pearson (14). pH values were determined, using a Radiometer pH meter 26, with a scale expander, on the meat slurry for microbial analyses.

RESULTS AND DISCUSSION

Bacterial counts

The aerobic plate count on the minced meat samples from the 12 different markets

(Table 1) ranged from 3.5 x 10s to 1.3 x 109 organisms/g. These counts were similar to those reported by Duitschaever et al (6) who found that 64% of samples of raw

refrigerated ground beef from 51 retail stores in Ontario, Canada, exceeded aerobic counts of 1.0 x 107 organisms/g. Only 6 of the 29 samples tested in this survey did not

exceed the total aerobic count standard of 1.0 x 107 organisms/g used by some states

in the United States (8) or the similar standard proposed by the Canadian Federal

Health Protection Branch (12). Only 1 of the 29 samples would have passed the more

stringent standard of 2.0 x 106 organisms/g proposed for minced meat by Murray (9). The use of aerobic plate count as an indicator of the quality of meat has been

questioned (20). It does not reflect the total viable count but only an approximation because competition occurs between the mixed microflora which require different

environmental conditions for optimum growth and many of the organisms grow in

pairs, clumps, chains, etc. Also, although a general relationship between total bacterial count and safety of the food exists, it is not consistent as evidenced by an outbreak

of scarlet fever in 1934 from low-count milk (20). There has been some recent evidence

of a poor correlation between total bacterial numbers and organoleptic properties




(20). However, aerobic plate counts do give some indication of the bacterial condition

affecting both the shelf-life and safety of the product (2). The coliform count from 11 different markets (Table 1) ranged from 1.9 x 103 to

3.0 x \06/g. In addition, examination of the EMB plates indicated that all samples had E. coli type organisms present, and six of the samples had E. aerogenes type present also.

None of the 22 samples tested would have satisfied the Oregon (8) or Canadian (12) standards of 50 and 100 coliform/g, respectively. However, 4 of the 22 samples tested

would be deemed satisfactory according to the more lenient standard proposed by Murray (9). Since most of the samples failed to satisfy any of the foregoing standards

the results suggest a low standard of hygiene and poor temperature control. The coagulase-positive staphylococci counts (Table 1) ranged from 1.0 x IO2 to

1.0 x 105/g. According to some workers (10), staphylococci should be absent from raw meat. However, since the counts in a number of the samples tested exceeded the

more lenient internationally accepted standard of 110 staphylococci/g, a potential health hazard could exist, in particular, if there was a time lag or lack of refrigeration before cooking. Fortunately in raw foods, like minced beef, with a natural microflora, the staphylococci will not grow to any significant extent due to competition from normal spoilage bacteria, particularly when the food is refrigerated (21).

pH values The pH values (Table 2) ranged from 5.62 to 6.90. A post-rigor pH of 6.0 has been

suggested as a cut-off value in assessing the quality of minced meat (14). In our study 9 out of 29 samples were judged unacceptable by both the pH value and total bacterial count. pH value as a spoilage index has been criticised because it does not appear to

correlate well with the number of microbes present and, also, a high pH value may exist in muscle due to physiological reasons, quite unconnected with bacterial spoilage.

However, the nearer the pH is to 7.0, the shorter is the expected shelf-life of the meat.

Extract release volume

The ERV (Table 2) ranged from 11.0 to 25.0 ml. A value of 20 ml has been sug

gested as a minimum for acceptability (22). Only 5 of the 29 samples met this require ment. More recently Pearson (14), on the basis of statistical correlation with odour

scores, found that most meats were considered acceptable provided the ERV was at least 17 ml. On the basis of this, 14 of the 29 samples would be deemed unacceptable.

The ERV has the advantage of being simple and rapid to perform but has been criticised for being unable to discriminate between acceptable and spoiled meat before off-odours and high microbial numbers occur (23).

Tyrosine value

The tyrosine values for the samples (Table 2) ranged from 26 to 85 mg tyrosine/ 100-g sample. A maximum level of 69.2 mg tyrosine/100-g sample has been suggested



5 I s 8

TABLE 1: Aerobic plate counts (APC), coliform counts and coagulase-positive Staphylococcus counts of minced beef at the time of purchase from 11 different markets (counts/g meat)

Sample 1 * Sample 2 Sample 3

Market APC APC Coliform Staphylococci APC Coliform Staphylococci

A 7.5 x 10* 2.4 X 107 3.0 x 10* 2.0 X 102 4.1 x 107 2.9 x 105 3.0 X 102

B ? 3.5 X 105 8.0 x 10* 1.0 X 102 3.0 x 10* 3.0 x 106 1.0 x 103

C 4.5 x 108 3.7 X 108 4.8 x 105 2.3 x 103 1.0 X 10? 4.0 x 103 None

D 6.5 X 106 3.2 X 106 4.2 x 105 None 1.9 x 107 1.3 x 105 None E 3.1 X 108 2.6 X 106 5.3 x 105 None 2.1 x 107 2.2 X 105 None

F 4.1 X 107 2.0 X 107 4.1 x 105 3.0 X 10* 2.7 X 107 2.4 X 105 7,0 x 102

G ? 4.4 X 107 1.9 X 103 None 2.3 X 108 3.3 x 105 1.0 x W

H ? 1.8 X 107 3.0 X 103 1.0 x 102 2.1 x 107 3.1 x 105 1.0 x 103

I 1.4 X 107 2.8 X 107 4.3 x 103 None 3.2 X 10? 3.5 X 105 None

J ? 2.9 X 108 3.0 X 106 2.0 X 102 1.5 x 107 6.0 x 104 1.0 x 102

K ? 1.3 X 109 3.0 X 106 None 1.1 X 10? 7.7 X 105 1.0 x 105

L_6.3 X 1QS_-._~-_--_~-_?_?

No coliform or staphylococci counts were made on Sample 1

TABLE 2: The pH, extract release volume (ERV) and total volatile nitrogen (TVN) of minced beef at the time of purchase from 12 different markets

Sample 1 Sample 2 Sample 3

ERV TV TVN ERV TV TVN ERV TV TVN Vfarket pH ml mg/lOOg mgN/lOOg pH ml mg/lOOg mgN/lOOg pH ml mg/lOOg mgN/lOOg

A 6.30 15.5 52.0 15.4 6.00 19.0 43.0 21.0 6.00 16.5 85.0 16.5

B ? ? ? ? 6.13 14.0 35.0 14.0 5.87 11.0 25.0 18.2

C 5.94 19.5 40.0 15.0 6.10 17.5 58.0 17.5 5.94 14.5 42.0 18.2 D 5.98 25.0 38.5 16.8 6.09 11.0 48.0 25.2 5.97 18.0 44.9 23.8 E 5.83 20.0 45.0 18.2 6.16 19.5 48.0 20.3 6.04 16.0 44.0 21.0 F 6.40 14.0 49.0 14.7 6.30 11.0 56.9 22.4 6.09 14.5 43.9 19.6

G ? ? ? ? 5.95 18.0 44.9 18.2 5.80 21.0 46.8 16.9

H ?-_.-__._ 5.80 15.5 38.1 21.0 6.05 17.5 32.0 25.2

I 5.62 20.0 32.0 13.7 5.82 19.5 43.0 18.2 6.09 13.5 35.0 30.8

J ? ? ? ? 5.83 19.0 41.0 25.2 5.83 20.0 40.0 18.2 K ? ?. ? ? 6.03 14.0 41.0 39.2 6.46 12.5 41.0 25.2

L 6.90 13.5 65.0 22.4 _- ? ? ? ? ? ̂ ?




(24). Only one sample in the present study failed to satisfy this standard. This test does not appear to be a very sensitive screening procedure as judged by some of the

high total bacterial counts, coliform counts and pH values.

Total volatile nitrogen TVN values ranged from 13.7 to 39.2 mg N/100-g sample (Table 2). A maximum

level of 21.1 mg N/100-g sample has been reported to be just acceptable while a level of 16.5 mg N/100-g sample was found acceptable (14). Only 9 of 29 samples exceeded the 'just acceptable' value. Like the tyrosine value, the TVN does not appear to be

very sensitive. The suitability of using either the tyrosine value or TVN to determine the incipient stages of spoilage is doubtful; and in this respect the present survey appears to confirm the findings of other workers, namely, that both the tyrosine value and TVN techniques only indicate advanced signs of spoilage which would already be obvious sensonly (25, 26).

TABLE 3: Samples from the various markets judged unacceptable by various tests

Tests*

Market Sample 2 Sample 3

A 1,2,3 1,2,3,5,6 B 2,3,4,5 2,3,5 C 1,2,3,4,5 1,2,5 D 2,3,5,7 1,2,7

E 2,4 1,2,4,5 F 1,2,3,4,5,7 1,2,3,4,5

G 1,2 1,2,3 H 1,2,3,5 1,2,3,4,5,7

I 1,2 1,2,4,5,7 J 1,2,3,5,7 1,2,3

K 1,2,4,5,7 1,2,3,4,5,7

1 ? TBC 5 - ERV 2 ? Coliform count 6 *= Tyrosine value 3 Coagulase-positive Staphylococcus 7 m TVN 4 m pH

Table 3 shows the frequency with which the samples failed to meet the various standards (statutory and proposed). It is seen that the coliform standard is the most

stringent. The present results further indicate that the coliform test could be used as an alternative to total plate count. In view of the relative poor quality of the meat in the present study, the usefulness of the various chemical parameters is difficult to assess. In general, the proposed chemical indices would appear to be less stringent

when compared to the bacteriological standards.

Finally, it is important that industry and public health authorities have a knowl

edge of the norm in carrying out their work so that, on the one hand, a realistic and

attainable standard can be proposed and, on the other, that the industry is prepared



DALY ET AL: MINCED BEEF 289

to meet any standards that may eventually be adopted. It is only by means of inspec tion that it is possible to establish a standard which can be used for meat quality improvement as a sanitation inspection tool in the meat market.

ACKNOWLEDGMENTS

The authors wish to thank the National Science Council, Dublin, for a grant to finance this project.

REFERENCES

1. Dainty, R. H., /. Fd Technol. 6: 209, 1971. 2. Elford, W. C, Am. J. publ. Hlth 26: 1204, 1936. 3. Foltz, V. D., /. Bact. 42: 289, 1941. 4. Kirsch, R. H., Berry, F. E? Balwin, C. L. and Foster, E. M., Fd Res. 7: 495, 1952. 5. Thienlin, G., Pantaleon, J. and Rosset, R., Annls Inst. Pasteur Lille 17: 131, 1966. 6. Duitschaever, C. L., Arnott, D. R. and Bullock, D. H., J. Milk Fd Technol. 36: 375, 1973. 7. Weinzirl, J. and Newton, E. M., Am. J. publ. Hlth 4: 413, 1914. 8. Carl, K. E., /. Milk Fd Technol. 38: 483,1975. 9. Murray, J. G., IFSTProc. 8: 81, 1975.

10. Elliott, R. P. and Michener, H. D., Appl. Microbiol. 9: 452, 1961. 11. Johnston, R. W., Proc. Meat Industry Res. Conf., American Meat Institute Foundation, p. 115,

1975. 12. Michaelson, P., Fd Can. 35(a): 38, 1975, 13. Pearson, D? /. Sci. Fd Agric. 19: 357,1968, 14. Pearson, D., /. Sci. Fd Agric. 19: 556, 1968. 15. Leach, T. M, R. Soc. Hlth J. 93: 248, 1973. 16. Campbell, J. J. R. and Konawalchuk, J., Can. J. Res. 26E: 327, 1948. 17. Difco Laboratories, Difco Supplementary Literature, Difco Laboratories Incorporated, Detroit,

p. 26, 1968. 18. Difco Laboratories, Difco Manual, 9th ed., Difco Laboratories Incorporated, Detroit, p. 330,

1971. 19. Jay, H. M., Fd Technol. 18: 129, 1964.

20. Wilson, G., Chemy Ind. 21: 273, 1970. 21. Skovgarrd, N., "Microbiological safety of food." Academic Press, Lond., p. 347,1973. 22. Pearson, DM FdMf. 42: 42,1967. 23. Ingram, M. and Dainty, R. H., /. appl. Bact. 34: 21, 1967. 24. Pearson, D., J. Sci. Fd Agric. 99: 366,1968. 25. Rogers, R. E. and McCleskey, C. S., Fd Technol 15: 210, 1961. 26. Gardner, G. A. and Stewart, D. J., /. appl. Bact. 29: 365,1966.

Received April 5,1976



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Quality of Raw Minced Beef