Microbial spoilage of meat and meat products

Meat is a term that refers to the edible parts of animals, such as muscles, fat, organs, and bones. Meat and its products are highly nutritious foods that provide protein, iron, zinc, vitamins, and minerals to humans. Meat can be obtained from various sources, such as poultry (chicken, turkey, duck), red meat (beef, pork, lamb, goat), game (deer, rabbit, wild boar), and seafood (fish, shellfish). Meat can also be processed into various products, such as ham, bacon, sausage, salami, jerky, canned meat, and meatballs.

However, meat and its products are also highly perishable and prone to microbial spoilage. Microbial spoilage is the deterioration of food quality and safety caused by the growth and activity of microorganisms. Microorganisms can cause changes in the appearance, odor, flavor, texture, and nutritional value of meat. They can also produce toxins or cause infections that can harm human health. Microbial spoilage can occur at any stage of the meat production chain, from the farm to the fork.

The susceptibility of meat and its products to microbial spoilage depends on several factors, such as:

The intrinsic properties of meat: Meat has a high water activity (aw), which is a measure of the availability of water for microbial growth. Meat also has a neutral or slightly acidic pH (5.5-6.5), which is favorable for most microorganisms. Meat contains nutrients that microorganisms can use as energy sources, such as sugars, amino acids, vitamins, and minerals. Meat also has enzymes that can catalyze biochemical reactions that affect its quality and stability.
The extrinsic properties of meat: These include the environmental conditions that affect meat during handling, processing, storage, and distribution. Temperature is one of the most important factors that influence microbial spoilage. High temperatures can accelerate microbial growth and activity, while low temperatures can slow them down or inhibit them. Other factors include oxygen availability (aerobic or anaerobic), relative humidity (moist or dry), light exposure (visible or UV), and packaging methods (vacuum or modified atmosphere).
The microbial load and diversity of meat: This refers to the number and types of microorganisms that are present on or in meat. The microbial load and diversity depend on the source and health status of the animal, the hygiene and sanitation practices during slaughtering and processing, the contamination from equipment and personnel during handling and distribution, and the cross-contamination from other foods or surfaces during storage and preparation.

Some of the common microorganisms that cause spoilage of meat and its products are bacteria (such as Pseudomonas spp., Acinetobacter spp., Brochothrix thermosphacta, Lactobacillus spp., Enterobacteriaceae spp., Staphylococcus spp., Clostridium spp.), molds (such as Penicillium spp., Aspergillus spp., Cladosporium spp.), yeasts (such as Candida spp., Rhodotorula spp.), and parasites (such as Trichinella spp., Toxoplasma gondii). Some of these microorganisms can also be pathogenic to humans (such as Salmonella spp., Campylobacter spp., Escherichia coli O157:H7, Listeria monocytogenes).

Therefore, it is important to understand the factors that affect the microbial spoilage of meat and its products and to apply appropriate methods to prevent or control it. Some of these methods include:

Good hygiene practices: These include washing hands and utensils before and after handling meat; cleaning and sanitizing equipment and surfaces; avoiding cross-contamination; using potable water; wearing protective clothing; following personal hygiene rules; inspecting raw materials; separating raw and cooked foods; disposing waste properly; training staff on food safety.
Good manufacturing practices: These include following standard operating procedures; monitoring critical control points; applying hazard analysis and critical control point (HACCP) principles; using approved additives and preservatives; maintaining proper temperature and humidity; using appropriate packaging materials; labeling products correctly; tracing products throughout the supply chain.
Good storage practices: These include storing meat at refrigeration (4°C) or freezing (-18°C) temperatures; using first-in first-out (FIFO) system; checking expiration dates; rotating stock; avoiding temperature abuse; protecting products from light exposure; preventing insect or rodent infestation.
Good preparation practices: These include thawing frozen meat in the refrigerator or under cold running water; cooking meat to a safe internal temperature (71°C for poultry, 63°C for pork, 71°C for ground meat, 63°C for whole cuts of beef or lamb); using a clean thermometer to check the doneness; resting meat before serving; reheating leftovers to 74°C; discarding spoiled or suspicious products.

By following these practices, we can ensure the quality and safety of meat and its products and prevent microbial spoilage. In the next sections, we will discuss the sources and causes of microbial contamination of meat, the events that take place during rigor mortis after the slaughter of the animal, the spoilage of fresh meat by enzymes and microbial action, the types of spoilage of meat under aerobic and anaerobic conditions, the defects caused by microorganisms on fresh meat, the spoilage of refrigerated meat by psychrophilic organisms, and the spoilage of cured meat and its long shelf-life compared to fresh and raw meat.

Meat spoilage can be caused by natural processes, such as lipid oxidation or autolytic enzymatic that occurs in the muscle after slaughtering. However, the most common and significant cause of meat spoilage is microbial contamination. Microorganisms can contaminate meat at various stages of production, processing, distribution, and storage. The sources and causes of microbial contamination of meat can be classified into three categories: animal-related, environment-related, and human-related.

The animal itself is a major source of microorganisms that can contaminate meat. The skin, hair, feathers, hooves, and intestinal tract of the animal harbor a diverse and complex microbial flora that can include spoilage and pathogenic microorganisms. Some examples of animal-related microorganisms are Staphylococcus aureus, Salmonella enterica, Campylobacter jejuni, Escherichia coli O157:H7, Clostridium perfringens, Clostridium botulinum, and Toxoplasma gondii. These microorganisms can be transferred to the carcass during slaughtering, skinning, evisceration, and dressing operations. The contamination can be influenced by factors such as the health status, stress level, diet, hygiene, and origin of the animal.

The environment in which the animal is raised, transported, slaughtered, processed, and stored can also introduce microorganisms to the meat. The environment includes the soil, water, air, feed, bedding, equipment, utensils, vehicles, facilities, and packaging materials that come in contact with the animal or the meat. Some examples of environment-related microorganisms are Pseudomonas spp., Acinetobacter spp., Moraxella spp., Brochothrix thermosphacta, Lactobacillus spp., Enterococcus spp., Bacillus spp., Mucor spp., Penicillium spp., and Candida spp. These microorganisms can cause spoilage or deterioration of meat quality by producing off-odors, off-flavors, slime formation, discoloration, gas production, or texture changes. The contamination can be influenced by factors such as the temperature, humidity, oxygen level, sanitation level, and storage time of the environment.

The human factor is another important source and cause of microbial contamination of meat. The human factor includes the workers who handle the animal or the meat at different stages of production and processing. The hands, clothing, gloves, knives, cutting boards, and other tools used by the workers can harbor microorganisms that can contaminate the meat. Some examples of human-related microorganisms are Staphylococcus epidermidis, Staphylococcus saprophyticus, Streptococcus pyogenes, Streptococcus agalactiae, Enterobacter spp., Klebsiella spp., Proteus spp., Serratia spp., and Yersinia enterocolitica. These microorganisms can cause spoilage or foodborne illnesses by producing toxins or invading the tissues of the meat. The contamination can be influenced by factors such as the hygiene practices, training, education, and awareness of the workers.

In conclusion, microbial contamination of meat is a complex and multifactorial phenomenon that can occur at any stage of production, processing, distribution, and storage of meat. The sources and causes of microbial contamination can be animal-related, environment-related, or human-related. The type and extent of contamination depend on various factors that affect the survival and growth of microorganisms on meat. Microbial contamination can have negative impacts on the quality, safety, and shelf life of meat products. Therefore, it is essential to implement good hygiene practices, sanitation measures, temperature controls, and other preventive strategies to minimize microbial contamination and spoilage of meat.

Rigor mortis is the stiffening of the muscles that occurs after death due to the depletion of adenosine triphosphate (ATP), the energy molecule of the cells. Rigor mortis affects the quality and shelf life of meat, as it influences its tenderness, water-holding capacity, color, and microbial spoilage. The onset and duration of rigor mortis depend on several factors, such as the type and condition of the animal, the ante-mortem and post-mortem handling, the temperature and pH of the carcass, and the presence of oxygen and enzymes. The main events that take place during rigor mortis are:

Respiration ceases, which stops ATP synthesis and oxygen supply to the cells. This leads to a reduction of oxidation-reduction potential in the muscle tissue, which affects the microbial growth and lipid oxidation.
The lack of ATP causes stiffening of muscle, as it prevents the detachment of actin and myosin filaments, the proteins responsible for muscle contraction and relaxation. The muscle fibers become rigid and shorten, resulting in a decrease in muscle volume and an increase in tension.
Glycolysis begins, in which most glycogen, the stored form of glucose in the muscle, is converted to lactic acid by anaerobic respiration. Lactic acid accumulates in the muscle tissue and lowers its pH from about 7.0 to 5.5-5.9. The pH drop affects the activity of enzymes, the solubility of proteins, the water-binding capacity of meat, and the growth of microorganisms.
The loss of vitamins and antioxidants causes the development of rancidity, as unsaturated fatty acids in the muscle are oxidized by oxygen and free radicals. Rancidity imparts off-flavors and off-odors to meat and reduces its nutritional value.
The ending of a reticuloendothelial system leads to the susceptibility of meat to microorganisms, as the immune system of the animal stops functioning after death. The microorganisms that contaminate meat can originate from various sources, such as the animal`s skin, gastrointestinal tract, lymph nodes, blood, or environment.
Nervous and hormonal regulations cease, thereby causing the temperature of the animal to fall and fat to solidify. The temperature drop affects the rate of biochemical reactions and microbial growth in meat. The solidification of fat affects the texture and flavor of meat.
Various metabolites accumulate that also aid protein denaturation, such as ammonia, urea, creatine, creatinine, and inosine monophosphate (IMP). Protein denaturation affects the water-holding capacity, tenderness, color, and flavor of meat.

Rigor mortis is usually resolved within 24 hours after slaughter, as proteolytic enzymes break down the actin-myosin complex and restore some flexibility to the muscle fibers. However, some factors can prolong or shorten rigor mortis, such as stress, stunning methods, electrical stimulation, chilling rate, or aging time. Therefore, proper management of rigor mortis is essential to ensure meat quality and safety.

Fresh meat is subjected to spoilage by its own enzymes and microbial action. The autolytic changes cause proteolytic action on muscle and connective tissue and hydrolysis of fats. These changes result in the development of off-odors, off-flavors, discoloration, and softening of the meat texture.

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 has pH (5.5-5.9) and Aw (0.85) values that favor 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 under different atmospheric conditions:

Spoilage under aerobic condition: This occurs when meat is exposed to air or oxygen-rich packaging. The aerobic spoilage is mainly caused by Pseudomonas spp., which produce slime, greenish discoloration, and ammonia-like odor. Other aerobic spoilage bacteria include Acinetobacter spp., Moraxella spp., Flavobacterium spp., Alcaligenes spp., and Micrococcus spp. These bacteria can also produce pigments, acids, aldehydes, ketones, and sulfur compounds that affect the color, flavor, and odor of meat.
Spoilage under anaerobic condition: This occurs when meat is vacuum-packed or stored in modified atmosphere packaging (MAP) with low oxygen and high carbon dioxide levels. The anaerobic spoilage is mainly caused by lactic acid bacteria (LAB), which produce sour odor and taste due to the production of lactic acid and other organic acids. Other anaerobic spoilage bacteria include Clostridium spp., which can produce gas, off-odors, and toxins; Enterobacteriaceae spp., which can produce hydrogen sulfide and indole; and Brochothrix thermosphacta, which can produce slime and brownish discoloration.

The spoilage of fresh meat can be prevented or delayed by applying various preservation methods such as chilling, freezing, heating, drying, salting, smoking, irradiation, high pressure processing, or adding antimicrobial agents or natural preservatives.

Meat spoilage can occur under different conditions depending on the availability of oxygen. Oxygen is an important factor that influences the growth and metabolism of microorganisms on meat. Depending on the presence or absence of oxygen, meat spoilage can be classified into two types: aerobic and anaerobic.

Aerobic spoilage

Aerobic spoilage occurs when meat is exposed to air and oxygen. This condition favors the growth of aerobic bacteria, yeasts, and molds that can utilize oxygen for their respiration and energy production. Aerobic spoilage is characterized by the following changes in meat:

Off-odors and off-flavors: Aerobic bacteria, such as Pseudomonas, Acinetobacter, Moraxella, and Flavobacterium, produce various volatile compounds, such as ammonia, hydrogen sulfide, indole, skatole, amines, aldehydes, ketones, and organic acids, that cause unpleasant odors and flavors in meat. These compounds are the result of the breakdown of proteins, amino acids, fats, and carbohydrates by bacterial enzymes. Aerobic yeasts, such as Candida and Torulopsis, can also produce off-odors by fermenting sugars and producing alcohols and aldehydes.
Discoloration: Aerobic bacteria can cause discoloration of meat by producing pigments, such as melanin, carotenoids, flavins, and porphyrins. These pigments can range from brown to green to red depending on the bacterial species and the substrate. For example, Pseudomonas fluorescens can produce green pigments by oxidizing pyocyanin. Aerobic molds can also cause discoloration of meat by producing spores and mycelia that have different colors. For example, Penicillium can produce blue-green spores and Aspergillus can produce black spores on meat.
Slime formation: Aerobic bacteria can produce slime or biofilms on the surface of meat by secreting extracellular polysaccharides (EPS). These EPS can trap water and nutrients and provide protection and attachment for the bacteria. Slime formation can result in a sticky or slimy texture and appearance of meat. Slime formation can also reduce the water activity (aw) of meat and increase its pH, which can favor the growth of other spoilage microorganisms. Aerobic yeasts can also produce slime by fermenting sugars and producing polysaccharides.
Gas production: Aerobic bacteria can produce gas bubbles in meat by fermenting carbohydrates or reducing nitrates. Gas production can result in swelling or bloating of meat packages or containers. Gas production can also cause physical damage to the meat tissue and increase its pH. The gases produced by aerobic bacteria include carbon dioxide, hydrogen, nitrogen, oxygen, methane, hydrogen sulfide, nitrous oxide, and nitric oxide.

Anaerobic spoilage

Anaerobic spoilage occurs when meat is deprived of oxygen or sealed in airtight containers or packages. This condition favors the growth of anaerobic bacteria or facultative anaerobic bacteria that can grow without oxygen or switch to anaerobic respiration or fermentation. Anaerobic spoilage is characterized by the following changes in meat:

Souring: Souring of meat is caused by the production of organic acids by anaerobic bacteria. These acids lower the pH of meat and give it a sour taste. The most common acid-producing bacteria are lactic acid bacteria (LAB), such as Lactobacillus, Leuconostoc, Pediococcus, Streptococcus, and Enterococcus. LAB ferment sugars and produce lactic acid as the main end product. Other acid-producing bacteria include propionic acid bacteria (PAB), such as Propionibacterium and Bifidobacterium; butyric acid bacteria (BAB), such as Clostridium; acetic acid bacteria (AAB), such as Acetobacter; and succinic acid bacteria (SAB), such as Veillonella.
Putrefaction: Putrefaction of meat is caused by the breakdown of proteins and amino acids by anaerobic bacteria. These bacteria produce various foul-smelling compounds, such as ammonia, hydrogen sulfide, mercaptans, indole, skatole, cadaverine, putrescine, histamine, tyramine, phenol, cresol, and indole. These compounds are toxic and carcinogenic and cause food poisoning if ingested. The most common putrefactive bacteria are proteolytic clostridia (PC), such as Clostridium perfringens, Clostridium sporogenes, Clostridium botulinum, and Clostridium tetani. PC hydrolyze proteins and produce ammonia, hydrogen sulfide, amines, and organic acids. Other putrefactive bacteria include proteolytic bacilli (PB), such as Bacillus subtilis, Bacillus cereus, and Bacillus megaterium; and proteolytic enterobacteria (PE), such as Escherichia coli, Proteus, Salmonella, Shigella, and Yersinia.
Gas production: Anaerobic bacteria can produce gas bubbles in meat by fermenting carbohydrates or reducing nitrates or sulfates. Gas production can result in swelling or bloating of meat packages or containers. Gas production can also cause physical damage to the meat tissue and increase its pH. The gases produced by anaerobic bacteria include carbon dioxide, hydrogen, nitrogen, methane, hydrogen sulfide, nitrous oxide, nitric oxide, and sulfur dioxide.

Defects caused by microorganisms on fresh meat

Fresh meat is a highly perishable food that can be easily spoiled by microbial growth, oxidation, and enzymatic autolysis. The nutrient breakdown in meat by microbial growth and autolysis results in the development of off-odors and flavors, slime formation, and discoloration, thereby making it unacceptable for human consumption. The main defects observed in meat are:

Discoloration: The color of fresh meat is mainly determined by the pigment myoglobin and its derivatives. Microbial growth can affect the color of meat by reducing the oxygen content, producing hydrogen sulfide, altering the pH, or producing pigmented metabolites. For example, Pseudomonas spp. can cause green discoloration of meat by producing fluorescent pigments . Clostridium spp. can cause blackening of meat by producing hydrogen sulfide. Lactic acid bacteria can cause browning of meat by lowering the pH and enhancing the oxidation of myoglobin.
Off-odors and off-flavors: The odor and flavor of fresh meat are mainly influenced by the volatile compounds produced by microbial metabolism. Microorganisms can degrade proteins, amino acids, carbohydrates, lipids, and other compounds in meat and produce various volatile substances that impart unpleasant odors and flavors to meat. For example, Pseudomonas spp., Moraxella spp., Acinetobacter spp., and Shewanella putrefaciens can produce ammonia, amines, sulfides, aldehydes, ketones, alcohols, and organic acids that cause sour, putrid, rancid, or fishy odors . Enterobacteriaceae can produce indole, skatole, phenol, cresol, and mercaptans that cause fecal or musty odors. Lactic acid bacteria can produce acetic acid, propionic acid, butyric acid, diacetyl, and acetoin that cause sour or buttery odors.
Gas production: Some microorganisms can produce gas as a result of their fermentation or respiration processes. Gas production can cause swelling or bloating of meat packages or containers. It can also affect the texture and appearance of meat by causing bubbles or cavities in the muscle tissue. For example, Clostridium spp., Enterobacteriaceae, and lactic acid bacteria can produce carbon dioxide, hydrogen, nitrogen, or methane as a result of their anaerobic fermentation of carbohydrates . Pseudomonas spp., Moraxella spp., Acinetobacter spp., and Shewanella putrefaciens can produce hydrogen sulfide as a result of their aerobic respiration of sulfur-containing amino acids .
Slime formation: Some microorganisms can produce extracellular polysaccharides (EPS) that form a slimy layer on the surface of meat. Slime formation can affect the texture and appearance of meat by making it sticky or slippery. It can also facilitate the attachment and growth of other microorganisms on meat. For example, Pseudomonas spp., Moraxella spp., Acinetobacter spp., Alcaligenes spp., Flavobacterium spp., Aeromonas spp., Leuconostoc spp., Weissella spp., and Bacillus spp. can produce EPS that form slime on meat .

The type and extent of microbial defects on fresh meat depend on various factors such as the initial contamination level, the type and diversity of microorganisms present, the intrinsic properties of meat (such as pH, water activity, nutrient content), the extrinsic conditions (such as temperature, oxygen availability, packaging method), and the storage duration.

Spoilage of refrigerated meat by psychrophilic organisms

Refrigerated meat is meat that is stored at low temperatures (usually between 0°C and 7°C) to slow down the growth of spoilage and pathogenic microorganisms and extend its shelf life. However, refrigeration does not completely prevent microbial spoilage, as some microorganisms can grow at low temperatures. These are called psychrophilic or psychrotrophic microorganisms, and they include bacteria, yeasts, and molds. Psychrophilic microorganisms can cause various defects in refrigerated meat, such as slime formation, off-odors, off-flavors, discoloration, gas production, and texture changes. Some psychrophilic microorganisms can also produce toxins or cause infections in humans.

The most common psychrophilic bacteria that spoil refrigerated meat are Pseudomonas spp., Acinetobacter spp., Moraxella spp., Aeromonas spp., Alcaligenes spp., Brochothrix thermosphacta, and lactic acid bacteria (LAB). Pseudomonas spp. are the dominant spoilage bacteria in refrigerated meat, as they can grow rapidly and produce proteolytic and lipolytic enzymes that degrade meat proteins and fats. Pseudomonas spp. can cause green discoloration, sour odor, and bitter flavor in refrigerated meat. Acinetobacter spp. and Moraxella spp. can also produce green pigments and slime on the surface of refrigerated meat. Aeromonas spp. and Alcaligenes spp. can produce hydrogen sulfide gas that causes blackening of meat. Brochothrix thermosphacta is a Gram-positive bacterium that can produce lactic acid and acetic acid that lower the pH of meat and cause sour odor and flavor. LAB are also Gram-positive bacteria that can produce lactic acid and other organic acids that inhibit the growth of other spoilage bacteria but also cause souring of meat.

The most common psychrophilic yeasts that spoil refrigerated meat are Candida spp., Torulopsis spp., Debaryomyces spp., and Rhodotorula spp. Yeasts can grow on the surface of refrigerated meat and produce slime, gas, and off-odors. Some yeasts can also produce pigments that cause pink or red discoloration of meat. The most common psychrophilic molds that spoil refrigerated meat are Alternaria spp., Cladosporium spp., Geotrichum spp., Mucor spp., Monilia spp., Penicillium spp., Sporotrichum spp., and Thamnidium spp. Molds can grow on the surface of refrigerated meat and produce mycelia, spores, toxins, and off-odors. Some molds can also produce pigments that cause black or green discoloration of meat.

The growth of psychrophilic microorganisms on refrigerated meat depends on several factors, such as the initial microbial load, the type and quality of meat, the temperature and duration of storage, the type of packaging, the oxygen availability, the pH and water activity of meat, and the presence of antimicrobial agents or additives in meat. To prevent or reduce the spoilage of refrigerated meat by psychrophilic microorganisms, some strategies can be applied, such as improving hygiene practices during slaughtering and processing of meat, reducing the temperature and time of storage, using modified atmosphere packaging (MAP) or vacuum packaging to limit oxygen exposure, adding salt, nitrite, spices, or other preservatives to inhibit microbial growth or activity, or applying physical treatments such as irradiation or high-pressure processing to reduce microbial load.

Spoilage of cured meat and its long shelf-life compared to fresh and raw meat

Cured meat is the meat that has been preserved by adding salt, nitrite, nitrate, sugar, spices, smoke, or other substances to inhibit microbial growth and enhance flavor. Curing can also involve drying, fermenting, canning, or vacuum packing the meat. Some examples of cured meat are ham, bacon, salami, jerky, corned beef, and canned meat.

Cured meat has a longer shelf-life than fresh and raw meat because curing reduces the water activity (aw) and pH of the meat, which are two important factors that affect microbial growth. Curing also introduces antimicrobial agents such as salt, nitrite, nitrate, organic acids, and smoke compounds that inhibit or kill spoilage and pathogenic microorganisms. Curing also modifies the color, texture, aroma, and taste of the meat, making it more appealing to consumers.

However, cured meat is not immune to spoilage. Microbial spoilage of cured meat can occur due to inadequate curing conditions, poor hygiene practices, contamination during processing or storage, or failure to maintain low temperature and oxygen levels. Microbial spoilage of cured meat can result in slime formation, gas production, off-odors, off-flavors, discoloration, texture changes, and reduced shelf-life.

The most common microorganisms that cause spoilage of cured meat are lactic acid bacteria (LAB), such as Lactobacillus sakei, Lactobacillus curvatus, Leuconostoc mesenteroides, and Leuconostoc carnosum. These bacteria can grow at low pH and aw and produce lactic acid and other organic acids that lower the pH further and cause souring of the meat. LAB can also produce diacetyl, acetaldehyde, acetoin, and other volatile compounds that contribute to off-flavors. LAB can also degrade nitrite and nitrate, which are important preservatives that prevent the growth of Clostridium botulinum and other pathogens.

Other microorganisms that can cause spoilage of cured meat include Enterobacteriaceae (such as Escherichia coli, Salmonella spp., Shigella spp., and Yersinia enterocolitica), Staphylococcus aureus, Bacillus spp., Clostridium spp., Pseudomonas spp., Acinetobacter spp., Moraxella spp., Brochothrix thermosphacta, Micrococcus spp., molds (such as Aspergillus spp., Penicillium spp., Rhizopus spp., and Thamnidium spp.), and yeasts (such as Candida spp., Debaryomyces spp., Torulopsis spp., and Trichosporon spp.). These microorganisms can grow at higher pH and aw than LAB and produce various enzymes that degrade proteins, fats, carbohydrates, and pigments in the meat. They can also produce ammonia, hydrogen sulfide, indole, skatole, mercaptans, and other foul-smelling compounds that cause putrefaction of the meat.

Some examples of defects caused by microorganisms in different types of cured meat are:

Slime formation on ham due to Leuconostoc mesenteroides
Souring of bacon due to Lactobacillus sakei
Greening of salami due to hydrogen peroxide production by Micrococcus spp.
Swelling of canned meat due to gas production by Clostridium spp.
Ropiness of sausage due to exopolysaccharide production by Alcaligenes viscolactis
Pink discoloration of cooked meat due to nitrite reduction by Enterobacteriaceae
Black spots on dry-cured ham due to mold growth

To prevent or minimize microbial spoilage of cured meat, several measures can be taken such as:

Using good quality raw materials with low microbial load
Applying adequate curing agents in appropriate concentrations and durations
Maintaining proper hygiene and sanitation during processing and handling
Controlling temperature and humidity during curing and storage
Using appropriate packaging materials and methods to exclude oxygen and moisture
Adding antimicrobial additives or cultures to inhibit or compete with spoilage microorganisms
Monitoring the microbial quality and safety of the product throughout its shelf-life.