Microbial spoilage of meat and meat products

Introduction

  • Meat and its product are highly nutritious food that is widely consumed by people all over the world.
  • Meat can be obtained from various birds (chicken, turkey, ducks, etc.) or mammals (pork, mutton, buffalo, sheep), and after slaughtering, carcasses and primary cuts are processed to raw or processed food products.
  • It is a nutritious, protein-rich food that is highly perishable and has a short shelf life.
  • The biological and chemical nature of meat leads to its deterioration from the time of slaughter until consumption. 
  • Meat and its products such as ham, sausages, cooked meat, dry meats, smoked meats, vacuum-packed meat, minced meat, etc. are all susceptible to microbial spoilage.
Microbial spoilage of meat and meat products
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Contamination source and causes

Meat spoilage can be caused by natural processes, such as lipid oxidation or autolytic enzymatic that occurs in the muscle after slaughtering. Several factors are responsible for microbial contamination of meat such as:

  1. Bacterial flora of animal.
  2. Knives, utensils, hands, and clothing of the workers.
  3. Pre-slaughter handling of livestock and post-slaughter handling of meat.
  4. handling during slaughtering, evisceration, and processing
  5. temperature controls during slaughtering,
  6. processing and distribution
  7. type of packaging used
  8. Handling and storage 

A series of the event takes place during rigor mortis after the slaughter of the animal such as:

  1. Respiration ceases, which stops ATP synthesis.
  2. The lack of ATP causes stiffening of muscle
  3. Reduction of oxidation-reduction potential due to lack of oxygen
  4. The loss of vitamins and antioxidants causes the development of rancidity.
  5. Glycolysis begins in which most glycogen is converted to lactic acid that reduces pH
  6. The ending of a reticuloendothelial system leads to the susceptibility of meat to microorganisms.
  7. Nervous and hormonal regulations cease, thereby causing the temperature of the animal to fall and fat to solidify.
  8. Various metabolites accumulate that also aid protein denaturation.

Spoilage of fresh meat

  • Fresh meat is subjected to spoilage by its enzymes and microbial action.
  • The autolysis changes cause proteolytic action on muscle and connective tissue and hydrolysis of fats.
  • The survival and growth of microorganisms are influenced by the composition of the atmosphere surrounding the meat.
  • Fresh meat contains nutrients such as sugars, amino acids, vitamins, cofactors, etc and it had pH (5.5-5.9) and Aw (0.85) values that influence the growth of microorganisms.
  • The most common bacteria isolated from fresh meat are bacteria of the genera Acinetobacter, Pseudomonas, Brochothrix thermosphacta, Flavobacterium, Psychrobacter, Moraxella, Staphylococci, Micrococci, lactic acid bacteria (LAB), and various genera of the Enterobacteriaceae.
  • The microbial pathogens found in fresh meat are Salmonella, Campylobacter, E.coli, Listeria monocytogenes.

There are two types of spoilage of meat:

  1. Spoilage under aerobic condition
  2. Spoilage under anaerobic condition

The kind of defects caused by microorganisms on fresh meat

Condition Kind of defects Microorganisms
Aerobic condition Surface slime Pseudomonas, Moraxella, Streptococcus, Bacillus, micrococcus 
The red color of meat called “bloom” caused by the production of an oxidizing compound Lactobacillus, Leuconostoc
Oxidative rancidity Pseudomanas spp, Archromobacter
Red spot Serratia marcescens, 
Blue color Pseudomonas syncyanea
Greenish blue or brownish black spot Chromobacterium lividum
Stickiness, whiskers, Green patches Mold

 

Anaerobic condition Putrefaction Clostridium  spp, Alcaligennes, Proteus
Souring Lactic acid bacteria

Spoilage of meat

  • Microbial growth, oxidation, and enzymatic autolysis are the three basic mechanisms responsible for the spoilage of meat.
  • The nutrient composition, high water content, and moderate pH of meat make it an excellent medium for microbial growth.
  • The normal flora of an animal’s lymph nodes contaminating meat is Staphylococcus, Streptococcus, Clostridium, and Salmonella.
  • Meat may contain different bacteria that include species of Acinetobacter, Aeromonas, Alcaligenes, Alteromonas, Brochothrix, Carnobacterium, Escherichia, Enterobacter, Enterococcus, Flavobacterium, Lactobacillus, Leuconostoc, Micrococcus, Proteus, Pseudomonas, Sarcina, Serratia, and Streptococcus.
  • Pathogenic microbial species contaminating meat are Salmonella enteric strains, Yersinia enterocolitica, Campylobacter jejuni, Aeromonas hydrophila, Listeria monocytogenes, and Escherichia coli
  • Mold species found in meat include Cladosporium, Sporotrichum, Geotrichum, Penicillium, and Mucor while yeasts species include Candida spp., Cryptococcus spp., and Rhodotorula spp.
  • The main defects observed in meat are off-odor, off-flavor, discoloration, and gas production.

Some defects caused by microorganism in different kinds of meat are:

Products Defects Microorganisms
Vacuum packed meat Sulfide odor Clostridium spp., Hafnia spp.
H2S greening Shewanella spp.
Blown Pack Clostridium spp., lactic acid bacteria
Fresh meat Putrefaction Alcaligenes, Clostridium, Chromobacterium, Proteus vulgaris, Pseudomonas fluorescens
Souring Chromobacterium, Pseudomonas
Cured meat Moldy odor Aspergillus, Penicillium, Rhizopus
Greening Pediococcus, Streptococcus
Souring Micrococcus, Pseudomonas
Slimy  Leuconostoc
Modified atmosphere packaging meats Souring, off-odor  Leuconostoc, Lactobacillus
Souring B. thermosphacta
Refrigerated packaged meat Off-flavors, slime, putrefaction Pseudomonas, Acinetobacter, Moraxella
sour, slime, and flavor change Lactic acid bacteria

Spoilage of refrigerated meat

  • When fresh meat is refrigerated at 4 ± 1°C, they remain in good condition for 5-7 days
  • Refrigerated temperature favors the growth of psychrophilic organisms in due course of time.
  • The contaminations occur during slicing and serving operations, from hands, slicing machines, and other equipment. 
  • Inadequate hygiene can lead to meat contamination by spoilage and pathogenic microorganisms
  • The important bacterial genera associated with spoilage of refrigerated meat are Acinetobacter, Moraxella, Pseudomonas, Aeromonas, Alcaligenes, and Micrococcus.
  • The mold genera associated with spoilage of refrigerated meat are Alternaria, Cladosporium, Geotrichum, Mucor, Monilia, Penicillium, Sporotrichum, and Thamnidium; and yeast genera associated with spoilage of refrigerated meat are Candida, Torulopsis, Debaryomyces, and Rhodotorula.
  • Generally, Brochothrix thermosphacta and lactic acid bacteria are the bacteria that cause spoilage of refrigerated meat.
  • Pathogenic microorganisms found in refrigerated meats include C. botulinum type E, Yersinia enterocolitica, enteropathogenic Escherichia coli, Listeria monocytogenes, and Aeromonas hydrophila as they are capable of growing at temperatures below 5°C.

Spoilage of cured meat

  • Cured meat is the meats in which are preserved by aging, drying, canning, brining, or smoking for enhancement of flavor and to extends its shelf life.
  • Some examples of cured meats are sausage, bacon, salami, ham, canned meat, dry spicy meat, meat pickles, kebab, meatballs, meat patty, etc.
  • The cured meat has a long shelf-life compared to fresh and raw meat however they are not immune to spoilage.
  • The bacterial spoilage causing organisms in processed and cured meats are lactic acid bacteria (such as Lactobacillus sake, Lactobacillus curvatus, Leuconostoc gelidium, Leuconostoc carnosum, Leuconostoc mesenteroides), Acinetobacter, Bacillus, Micrococcus, Serratia, and Staphylococcus.
  • The spoilage causing  mold found in cured meat includes Aspergillus, Penicillium, Rhizopus, and Thamnidium
  • The spoilage causing yeast found in cured meat includes Candida, Debaryomyces, Torula, Torulopsis, and Trichosporon.
  • Other spoilage causing microorganism found in cured meats includes Clostridium spp, Hafnia spp, Weisella spp, Shewanella spp, Pseudomonas spp, Enterococcus spp, etc. 
  • The pathogenic microorganisms found in cured meat include Escherichia coli, Salmonella, Staphylococcus aureus, Listeria monocytogenes, Clostridium botulinum, and Toxoplasma gondii.
  • Microbial growth in cured meat can result in slime formation, structural components degradation, decrease in water holding capacity, off odors, and texture and changes in appearances.

Some defect in different cured meat products caused by microorganism are:

Cured meat products Defects  Microorganisms
Dried-fermented sausage small dark spot B.thermosphacta, Lactobacillus, Leuconostoc, Microbacterium, Micrococcus, Alternaria 
CO2 production heterofermentative LAB
Nitric oxide gas production nitrate-reducing bacteria
Greening with H2O2 heterofermentative Lactobacillus fructivorans, L. jensenii, L. viridescens, Leuconostoc, Enterococcus faecium, Enterococcus faecalis, Pediococcus
Slime layer on the surface Micrococcus and yeasts
fuzziness and discoloration Penicillum verrucosum

Aspergillus glaucus

Cured meats  H2S production Vibrio, Enterobacteriaceae
Bacon  Cabbage odor Providencia
white and gray or grayish-green spot Aspergillus, Alteraria, Fusarium, Mucor, Rizopus 
Ham Putrefaction Enterobacteriacae, Proteus
Souring Lactic acid bacteria, Enterococcus, Micrococcus, Bacillus, Clostridium
Bone taint  Serratia spp, Clostridium spp, Proteus spp
Red spot Halobacterium salinarum
Blue spot Pseudomonas syncyanea, Penicillum Soinulosum, Rhodotonela spp
Dark spot Alternaria
Sausages Souring, off-odor Lactic acid bacteria
Surface slime Bacillus, Lactobacillus, Leuconostoc
Greening Enterococcus, Lactobacillus, Leuconostoc, Pediococcus
Dried meats Surface slime Micrococcus
souring Halobacterium salinarum
Off-odor Flavobacterium
Blue color P. syncyanea, P. Spinulosum
red color Bacillus spp
Smoked products  Off-odor Micrococcus, yeasts, molds
Souring Lactobacillus Plantarum, L. Mesenteroides, Clostridium spp
Pickled meat Putrefaction Vibrio, Alcaligenes, Spirillum
souring Lactobacillus, Micrococcus
Slime formation Leuconostoc.

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1 thought on “Microbial spoilage of meat and meat products”

  1. Nice information for teaching purpose. Easy to understand to UG student. It shuld be ithe form of audio and Video recording.

    Reply

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