Microbiological and Chemical Quality of Cured and Salted Meats - January-March 1998

January - March 1998

OBJECTIVE

  • To determine the bacteriological status of salted and cured meat products available on the ACT market.
  • To determine the compliance of these products relative to standard requirements of nitrate and nitrite preservatives.
  • To determine the level of sodium and potassium in these products.

Background

These food product types can be purchased in tins, vacuum plastic wrap or are sold to the customer ready sliced. Product handling and storage processes can create conditions that are ideal for microbial growth, especially when incorrect preserving techniques are initially employed.

The process of curing or pickling meats is still common, but is limited mainly to bacon, hams and silverside products. The technique itself involves the addition of a brine solution usually consisting of salts including sodium chloride, sodium nitrate, sodium nitrite, and sugar. This chemically reacts with the tissue and involves the following (Ref_3):-

  • The salt dehydrates the meat, altering the water activity which inhibits bacterial growth and subsequent spoilage.
  • The sugar helps to soften the meat, counteracting the hardening effects of salt. It also interacts with amino acid which, upon cooking, enhances browning and the flavour of the meat.
  • Nitrite and nitrate are important to permit the stabilisation of colour to:
  • contribute to the characteristic flavour of the meat;
  • retard the development of rancidity; and,
  • inhibit the growth of a number food poisoning and spoilage bacteria.

Other chemicals that may also be used include phosphates, ascorbate/erythorbate and potassium chloride. The phosphates are added to increase the water-binding capacity and therefore the yield of the finished product (Ref_3). The salts of ascorbic and erythorbic acid are used to hasten development and stabilise the colour of cured meat by acting as an antioxidant. (Ref_3). Potassium chloride can be used to partially substitute sodium chloride addition. Lite Salt is a 50-50 commercial mixture of sodium and potassium chloride which is widely available for producers. The benefits of using this product include its cost effectiveness, it reduces intake of sodium from these products (beneficial in reducing blood pressure) and a reduction in salty taste (Ref_4).

The Standards Food Code (Ref_1) defines salted meat as that which has been cured in a salt solution without the addition of nitrate/nitrite. Cured meat is defined as that which has been cured with the addition of nitrite/nitrate.

Safety concerns have been expressed in the past with the use of nitrite/nitrate in foods. Nitrous acid, which is formed by the breakdown of nitrite, binds with amines in proteins to produce N-nitrosamines (Ref_4), which are known human carcinogens. N-nitrosamines have been isolated in small amounts from nearly all cured meat products. Research has been conducted into processing methods that would eliminate N-nitrosamines from cured meats, but still allow retention of nitrite because of its action in preventing the growth of Clostridium botulinum and other food poisoning organisms. It has generally been conceded that the risks from low levels of N-nitrosamines are less than those from botulism poisoning, which may occur if nitrites were removed from the cure (Ref_4). The addition of erythorbate and or ascorbate also reduces the formation of N-nitrosamines, so they are normally included (Ref_4).

Levels of Nitrates/nitrites

The Food Standards Code (Ref_1) limits the level of nitrite and nitrate found in the finished product with the following clauses:

Standard C1, 30:

  • Cured meat, except commercially sterile canned cured meat and slow dried cured meat, must not contain more than 125 mg/kg in total of nitrites and nitrates, calculated as sodium nitrite.

  • Commercially sterile canned cured meat must not contain more than 50 mg/kg in total of nitrites and nitrates, calculated as sodium nitrite.

  • Slow dried cured meat must not contain more than 500 mg/kg in total of nitrites and nitrates, calculated as sodium nitrite.

Microbiological Standards

There is a specific microbiological standard which applies to cooked cured or cooked salted meat.

Standard C1, clause 59 (Ref_1):

  • Cooked Cured Meat and Cooked Salted Meat when examined by Method 3.1 in the schedule, must have a coagulase-positive Staphylococci count not exceeding 100 coagulase-positive Staphylococci per gram.

There are no specific standards for uncooked cured or uncooked salted meat, so these food types are considered under the Food Act 1992 (Ref_2), which states:

A person shall not sell food that is injurious to health; unfit for human consumption; or so contaminated that it would be reasonable to expect it to be used for human consumption in that state.

Samples were tested for Coagulase positive Staphylococcus and the specific food pathogens Escherichia coli (E. coli) and Listeria monocytogenes (L. monocytogenes). Tables 1 & 2 below outline the acceptability criteria for tested microorganisms. The acceptability criteria were devised the Health Protection Service and based on ACT historical food data, W.A. microbiological guidelines (ref_5) including the level of concern based upon the food type and preservation procedures.

Table 1 - Uncooked cured and uncooked salted

 

Test Organism

Good

Poor

Unsatisfactory

Coagulase positive Staphylococcus

<50

<50-1000

>1000

E. coli

<2#

2 - 100

>100

L. monocytogenes

Not detected*

-

Detected*

 

#Units expressed in terms of colony forming units (cfu) per gram. *Organism detected/not detected in 25 gms

Table 2 - Cooked cured and cooked salted

 

Test Organism

Good

Poor

Unsatisfactory

Coagulase positive Staphylococcus

<100

 

>100

E. coli

<2#

2 - 100

>100

L. monocytogenes

Not detected*

-

Detected*

 

#Units expressed in terms of colony forming units (cfu) per gram. *Organism detected/not detected in 25 gms

SURVEY

In this survey, 65 samples of cured and salted meats were collected from supermarkets in the ACT. Samples consisted of ham, bacon, beef jerky, Hungarian presswurst, smoked beef, ox tongue, prosciutto, pancetta, capocollo pastrami, and silverside. It was difficult to adequately determine if the samples had been cooked after curing or salting and as a consequence most samples that were collected were not cooked cured or salted meats and therefore not subject to the ANZFA FSC standard. The silverside sample was an exception to this The In order to adequately collect samples of the myriad of types of product available on the ACT market, the survey examined one sample consisting of one subunit of each product. No sample consisted of five subunits as required by the Code.

RESULTS

Microbiological Testing

Coagulase-positive Staphylococcus

Coagulase-positive Staphylococcus was detected in 4 (6%) samples as indicated:

*This sample is not a cured or salted meat and was mistakenly taken.

The prosciutto was the only sample unsatisfactory for Coagulase-positive Staphylococcus. The pancetta result was regarded as been poor. The Silverside sample was only a single sample and therefore complied with the ANZFA FSC which allows a single sample to have up to 1000 coagulase positive Staphylococcus per gram of food. All other foods had acceptable results below the detection limit of < 50 cfu/g.

Escherichia coli

E. coli was also detected in four samples, as indicated:

 

Food E. coli count (cfu/g)
Ox tongue 210
Ox tongue 4
Bacon 4
Peppered ham 4

 

All other foods had acceptable results below the detection limit of <3 cfu/g. One sample of ox tongue (210 cfu/g) had unsatisfactory results.

Listeria monocytogenes

Only 61 of the 65 samples were tested for L. monocytogenes. L. monocytogenes was isolated from 9 samples (14.8%) representing 8 different foods. This included Square Ham, Raw Ham, Ox Tongue, Prosciutto, Middle Bacon Rashers (2), Bacon pieces, smoked beef and crisp and crinkly??????. The Prosciutto was the same food with the unsatisfactory coagulase positive Staphylococcus count.

DISCUSSION

Microbiological

The E. coli, and coagulase positive Staphylococcus results are encouraging with only 2 unsatisfactory results being detected. The unsatisfactory coagulase positive staphylococcus result for the Prosciutto product is however of concern. The L. monocytogenes being detected in 14.8% of these samples could be of concern depending on the level of the pathogen in the foods. A future survey should undertaken to determine the levels of Listeria monocytogenes in this type of food. All the samples of cured and salted meat except the silverside were not cooked so the ANZFA standard could not be applied. The single silverside sample complied with the ANZFA FSC.

CONCLUSION

The results of the sampling need to be monitored more closely as the food with the high level of coagulase positive Staphylococcus was not tested to see if the isolate produced staphylococcus enterotoxin or if the food had enterotoxin at levels likely to cause food poisoning.

RECOMMENDATIONS

Refer to recommendation document.

BIBLIOGRAPHY

Australia and New Zealand Food Authority, Food Standards Code, incorporating amendments up to and including Amendment 38, April 1998.

Food Act 1992 (ACT), reprinted as at 31 January 1996.

Desrosier, N.W, The Technology of Food Preservation, Fourth Edition, The Avi Publishing Company Inc., 1977.

A.M Pearson and T.A.Gillett, Processed Meats, 3rd Edition, Chapman and Hall, 1996.

Food Watch, Microbiological Guidelines for Ready-to-Eat Foods, , Western Australian Food Monitoring Program April 1999.

ACKNOWLEDGMENTS

Sampling Officers: Louisa Bartolome and Chris Wixon

Sample analysis: Microbiology and Food Chemistry, ACT Government Analytical Laboratory

E coli serotyping: Denise Murphy of the Queensland Health Scientific Services, Centre for Public Health Services.

Report: Simon Christen and Geoff Millard