The Meats We Eat, Odours, Micro-organisms, Food Poisoning, Spoilage, and Shit

Damage or injuries that make food undesirable for human consumption can be the result of:

1. deliberate contamination or poisoning.
2. disease
3.  insect damage
4. physical injury
5.  enzymatic degradation
6.  microbial activity

Do you have any idea, at all, of what you are talking about- you know, those things that you grew up knowing, those things everybody knows ALL ABOUT; or a least likes to BELIEVE they do?

Basic Types of Food Spoilage

Appearance: when a food “looks bad,” what is this referring to?

Microbial growth:

1.    mycelia or colonies visible on surface

2.    development of cloudiness in liquids

3.    changes in food colour due to heme or chlorophyll breakdown

4.    colony pigments, growth of mycelia, etc.

Textural changes (feel)

Slime formation;due primarily to surface accumulation of microbial cells; can also be a manifestation of tissue degradation.

Tissue softening due to enzymatic degradation (e.g. soft rot in veggies)

Changes in taste and odour

Development of:

1.    nitrogenous compounds (ammonia, amines, etch.)

2.    sulphides

3.    organic acids

The numbers and types of micro-organisms in a food are largely determined by:

1.    Environment from which the food was obtained.

2.    Microbiological quality of the food in its raw or unprocessed state (intrinsic factors).

3.    Handling and processing sanitation.

4.    Effectiveness of packaging, handling and storage conditions in restricting microbial growth (extrinsic factors).

Specific Food Groups

Fresh Meats: fresh meats are among the most perishable of all foods.

Chemical composition:

      -75% water

      -18% protein

      -3% fat, 1% ash, traces of CHO, vitamins, etch.

 Whole Meats:

The microflora of fresh meat is composed primarily of:

1.   Gram negative aerobic rods such as Pseudomonas, Acinetobacter and Moraxella.

2.   Bacillus and clostridia (e.g. C. perfringens) are also common on all types of meat.

Although subsurface portions of meat are generally sterile, some parts such as lymph nodes may be heavily contaminated.

Mechanical disruption-including but not exclusive to mechanical tenderization- of the tissue during processing can and does distribute micro-organisms from the meat surface throughout the product.

Although, according toCanadian law, it is illegal; pink slime is now present in at least 90% ofCanadian meat products. The slime does not have to appear on the label because, over objections of its own scientists, Canadian Government officials-with links to the beef industry- decided to label it “meat”.

The “pink slime” (much of which is produced in Mexico) is made by gathering waste trimmings, simmering them at low heat so the fat separates easily from the muscle, and spinning the trimmings using a centrifuge to complete the separation. Next, the mixture is sent through pipes where it is sprayed with ammonia gas to kill bacteria. The process is completed by packaging the “meat” into bricks. Then, it is frozen and shipped to grocery stores and meat packers, where it is added to most beef products(to be more truthful, it is added to almost ALL MEAT PRODUCTS, including fish, poultry and the notorious "highly processed" luncheon meats).

Handling, (how and the number of times) plus storage temperature; are the most important control factors for meat spoilage.

Other Sources of Contamination

Several genera of moulds grow on the surface of meat and can cause spoilage, but cannot grow on meat stored below 5oC.

Usually, fresh cut meats in the refrigerator at high humidity undergo bacterial spoilage by:

1.    Gram negative aerobes like Pseudomonas, Acinetobacter and Moraxella spp.The intrinsic and extrinsic parameters of ground beef favour these bacteria so strongly that they are almost exclusive spoilage agents.

2.    Meat spoilage is characterized by the appearance of “off” odours, and slime, which are manifest when surface loads exceed 107 CFU/cm2.The slime is due to the accumulation of bacterial cells. Interestingly, meat spoilage (including poultry and fish) occurs without any significant breakdown of the primary protein structure. Instead, spoilage bacteria utilize glucose, free amino acids or other simple nitrogenous compounds to attain population of about 108 CFU/cm2, at which point the organoleptic quality of the meat will clearly reveal it is spoiled.

   Ground Meats:

Same micro-organisms as whole meats, but always have higher microbial loads.  Why?    

1.    Greater surface area which gives microbes better access to the food and also traps air to favour the growth of gram-negative, aerobic bacteria like Pseudomonas spp.

2.  Every handling or processing (storage utensils, cutting knives, grinders) step can contribute additional contamination to the final product.One heavily contaminated piece (e.g. a lymph node) can contaminate an entire lot when they are ground together.

3.    Use of illegal soy protein extenders and mechanically de-boned meat not only changes the microflora significantly but alsoraises the pH of meat which leads to more rapid spoilage-normal ground beefpH=5.1-6.2, added extenders raise it to 6.0-7.0)

Vacuum packaged meats

-     80% of beef leaves packing plant in vacuum package.

-     not all O2 is removed during packaging but residual is consumed by respiration of aerobic MO and the tissue itself

-     results in increased CO2 levels and thus get a longer shelf life.

When Impermeable films used:

1.    CO2 levels are higher

2.    Eh lower

The microflora shifts from predominantly G- aerobes to G+ anaerobes and microaerophilic lactic acid bacteria (LAB) like Lactobacillus, Carnobacterium and Leuconostoc.

-     if nitrites have been added to the vacuum packaged meat (e.g. to inhibit C. botulinum in hams, bacon), LAB domination is even more pronounced

In general, vacuum packaged meats are considered very safe foods and free from most pathogenic species of bacteria; with the possible exception of S. aureus and Y. enterocolitica. At home, I vacuum package all foods whenever possible.

 Spoilage in vacuum packaged meats is manifest by:

1.    Slime development.

2.    Greening caused by microbial production H2O2 or H2S.H2O2 production in meat has been associated with several types of lactic acid bacteria (primarilyLactobacillus).The oxidant (H2O2-water) reacts with nitrosohemochrome (cured meat colour) to form a green porphyrin compound. H2S greening occurs in fresh meats that have been vacuum packaged and stored between 1-5oC.H2S reacts with myoglobin  to form sulphmyoglobin.

3.    in meats with a pH above 6.0.H2S is produced by Shewanella putrefaciens and Pseudomonas spp. (when O2- permeable films are used).Some lactobacilli (when O2- impermeable films are used).

“Off Odours” Which Result From:

1.    the release of short chain fatty acids

2.    the production of volatile compounds like acetoin, diacetyl and H2S (and many other compounds, depending on the dominant spoilage bacterium)

The type of spoilage bacteria that will dominate is influenced by several factors that include:

1.    Is the meat product raw or cooked?

Cooked products have a higher pH (>6.0) which may allow growth of G- facultative anaerobic pathogens like Yersinia enterocolitica.

Raw products have a pH of about 5.6 which favors lactic acid bacteria, esp. Lactobacillus, Carnobacterium, and Leuconostoc.

2.    Nitrite concentration in meat.

High nitrite conc. favors lactic acid bacteria.

Low nitrite levels may allow growth of Brochothrix thermosphacta (G+ rod, fac anaer, growth @ 0-30oC from pH 5.0-9.0 catalase+).

Thermosphacta is an important spoilage bacterium in anaerobically stored meats kept at low temperature, but the bacterium is inhibited by nitrite.

Highly Processed Meats, Including Bacon, Ham, Frankfurters, Other Sausages, Luncheon Meats, and Mechanically Tenderized Braising or Roasting Cuts.  

All of these products are composed of a variety of blended ingredients, any of which can contribute micro-organisms to the food.

Yeasts and bacteria are the most common causes of spoilage, which is usually manifest in 3 ways:

      A.   Slimy spoilage: like other meat products, this occurs on the surface and is caused by the buildup of cells of yeasts, lactobacilli, enterococci or Brochothrix thermosphacta.

Washing the slime off with hot water can restore the product quality.

      B.  Sour spoilage: results from growth of lactic acid bacteria (which originate from contaminated ingredients like milk solids or pink slime) under the casing.

These organisms ferment lactose and other CHOs in the product and produce organic acids.

Taste is adversely affected but the product-according to the Canadian Government and the Canadian Department of Health- is not harmful if eaten.

     C.  Greening, Due to H2O2 or H2S Production.

Because greening indicates more extensive product breakdown, I would not recommend eating any green highly processed meat products. All highly processed meatproducts have been linked to early death.

Reasons Cured Meats (bacon, hams) are or Were Resistant to Spoilage:

1.    Reduction of water content.

2.     Use of nitrite/nitrate.

3.    Smoking or brining of hams.

4.    The high fat content of side bacon, smoked jowl, and some other cuts

Instead, spoilage of these products is often caused by molds from several genera including Aspergillus, Fusarium, Mucor, Penicillium, Rhizopus and Botrytis.

Poultry:

      a.   general trends are the same as other fresh meats

      b.   similar microflora on fresh birds

      c.   whole birds have lower counts than cut-up parts

      d.   additional processing steps add to the microbial load

When poultry is in the advanced stages of spoilage, the skin will often fluoresce under UV because so many fluorescent pseudomonads are present.

As is true of most meats; off odours generally appear before sliminess develops.

The same bacteria can produce visceral taint, a condition manifest by off odours in the abdominal cavity of poultry.

Point to remember:

During the initial stages of spoilage, the skin supports bacterial growth better than does the tissue (which remains essentially free of bacteria for some time).  Thus, the skin can sometimes be removed to salvage the food.

 Fish:

a.   Fish have high nitrogen content but no carbohydrate.

b.   The microbial quality of fish and especially shellfish is heavily influenced by the quality of the water from which they were harvested.

c.   Unsanitized processing steps are principal culprits in fish products with high microbial loads.

d.   In general, frozen fish products have lower counts than fresh products.

e.   Bacteria on fresh fish are concentrated on the outer slime, gills and intestine.

f.    Spoilage of salt- and freshwater fish occurs in similar ways; the most susceptible    part of the fish to spoilage is the gill region, and the best way to detect spoilage in fresh fish is to sniff this area for off odours produced by Pseudomonas and Acinetobacter-Moraxella bacteria. The odours include ammonia, triethylamine, H2S and other compounds.

g.   If fish are not eviscerated quickly, bacteria will move through the intestinal walls and invade the meat that lies next to the abdominal cavity.

Spoilage of crustaceans (shrimp, lobsters, crabs and crayfish) is similar, but these products have some CHO (0.5%) and more free amino acids so spoilage can occur more rapidly.

Molluscs (oysters, clams, mussels, squid and scallops) have more CHO (3-5%) and less nitrogen than either fish or shellfish. Micro flora of molluscs can vary a great deal depending on the quality of the water from which they were harvested.

Shellfish are filter feeders and can be expected to contain almost any microorganism or virus that occurs in the water where they were obtained.

If these products were taken from clean waters, then the usual Pseudomonas and Acinetobacter-Moraxella types of spoilage bacteria dominate.

© Al (Alex-Alexander) D. Girvan. All rights reserved.