Causes of Meat Spoilage and Effective Preservation Techniques

Foods that are rich in nutrients and high in protein have a short shelf life unless preservation techniques are used. Many people throughout the world’s first pick for animal protein. Despite the fact that it is consumed and that there is a demand for it, a significant quantity of meat and meat products deteriorate every year. Microbial deterioration is responsible for a sizable amount of this loss. (Other reasons for spoilage of meat and meat products include lipid oxidation and autolytic enzymatic spoilage).

The transformation of animals into meat involves several operations.

• Handling and loading of animals on the farm.
• Transporting animals to slaughterhouses.
• Off-loading and holding of animals.
• Slaughtering of animals (involves stunning, bleeding, skinning, evisceration and carcass splitting).

Poor operational techniques and facilities in any of these operations will result in unnecessary suffering and injuries to animals which can lead to reduced meat quality and spoilage of meat. Meat is composed of up of fat, protein, minerals, carbohydrates, and water. Meat decaying causes lipid oxidation, protein breakdown, and the loss of other important components.

Causes of Meat spoilage

Meat is a nutritious, protein-rich food with a short shelf life since it is very perishable and cannot be preserved. The handling of cattle before slaughter and the handling of meat after slaughter both significantly contribute to a decrease in meat quality. Nutrition, transportation, marketing, lairaging, and stunning are a few of the pre-slaughter practices that affect meat deterioration. Microorganisms, lipid oxidation, and autolytic enzymatic spoilage are the major reasons of meat and meat products turning bad after being slaughtering as well as during processing and storage.

The glycogen content of animal muscles is reduced when the animals is exposed to pre slaughter stress which change the pH of the meat. Lactic acid is produced due to the breakdown of glycogen content of animal’s muscles. Higher level of Ph (6.4-6.8) result in Dark Firm and Dry (DFD) meat. Long term stress cause DFD meat which has a shorter shelf life. Severe short term stress results in a Pale Soft and Exudative (PSE) meat. PSE meat has lower PH than normal ultimate value of 6.2 which is responsible for the breakdown of proteins providing a favorable medium for the growth of bacteria.

1. Oxidation of lipids

Lipid oxidation in meats is a process whereby polyunsaturated fatty acid react with reactive oxygen species leading to a series of secondary reactions which in turn lead to degradation of lipids and development of oxidative rancidity. The meat and meat products industry is very interested in minimizing and controlling lipid oxidation. Technologies such as vacuum packing, modified atmospheres, and antioxidant use have been developed. The objective is to understand he lipid oxidation processes causing a reduction in the sensory and nutritional quality of meat and meat products and to determine the most effective methods to control his process. There are several methods for reducing lipid oxidation in meat, including processing, antioxidant addition, animal dietary supplements, and specialized packaging. Utilizing additional methods an focusing on preserving food safety as well as preventing damage to other sensory characteristics can lead to improved results.

2. Autolytic spoilage

After animal slaughter, enzymatic reactions occur naturally in the muscles and tissues of the animals and are the main factor in meat deterioration. Meat softens and turns green due to the tissue’s complex molecules (carbohydrate, fat, and protein) being broken down into simpler ones. Souring is a term for excessive autolysis.

3. Microbial spoilage

Several factors are responsible for microbial contamination of meat such as:

• Bacterial flora of animal.
• Knives, utensils, hands, and clothing of the workers.
• Pre-slaughter handling of livestock and post-slaughter handling of meat.
• Handling during slaughtering, evisceration, and processing.
• Temperature controls during slaughtering. 
• Processing and distribution.
• Type of packaging used.
• Handling and storage.

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

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

Learn more:

General Types of spoilage of Meat

Spoilage due to molds in aerobic condition

Molds are actively involved the spoilage meat in aerobic conditions. Common types of spoilage are listed in subsection.

• Stickiness: Budding growth of molds causes the surface of the meat sticky to the touch known as stickiness. Such types of spoilage result the unusual appearance of meat.
• Whiskers: A small amount of mycelial growth without sporulation may occur under freezing conditions and result in the growth known as whiskers. This type of white, fuzzy growth can be caused by a number of molds, including Thamnidium chaetocladioides, or T. elegans; Mucor mucedo, M. lusitanicus, or M. racemosus; Rhizopus, etc.
• Black spot:  Cladosporium herbarum is a mold commonly causes blackspots, however other molds with dark pigments may also be responsible.
• White spot: White spot can be caused by any mold with moist, yeast-like colonies, such as Geotrichum, although Sporotrichum carnis is the most common cause.
• Green patches: Penicillium such as P. expansum, P. asperulum, and P. oxalicum are responsible for the green patches on meat.

Spoilage under aerobic condition

• Surface slime: Spoilage of meat due surface slime is produced by species of Pseudomonas, Acinetobacter, Moraxella, Alcaligens, Micrococcus, Streptococcus, Leuconostoc, and Bacillus. Some species of lactobacillus also showed to produce slime. The thin film formation on meat provided microbes nutrients from the substrate.
• Changes in colour of meat pigments: As a result of bacteria producing oxidizing substances such peroxides or hydrogen sulfide, the red color of meat, known as its “bloom,” may change to green, brown, or grey. Sausage greening is believed to be caused by Leuconostoc and Lactobacillus species (mainly heterofermentative).
• Changes in fats: The oxidation of unsaturated fats in meat takes place chemically in air and may be catalyzed by light and copper. Both lipolysis and the oxidation of lipids may be accelerated by lipolytic bacteria. Yeasts and lipolytic species like Pseudomonas and Achromobacter can also contribute to the rancidity of lipids.
• Off odours and off tastes: Taints, or unpleasant flavors and odors, which develop in meat as a result of bacterial growth on the surface often, are apparent before other symptoms of spoilage. Volatile acids like formic, acetic, butyric, and propionic as well as the development of yeasts can cause meat to spoil. Stale flavor is also referred to as a “cold-storage flavor” or “taint.” A musty or earthy taste might be caused by actinomycetes. The growth of yeasts on the surface of meats in aerobic circumstances can result in sliminess, lipolysis, unpleasant flavors and odors, as well as discolorations that can be white, cream, pink, or brown because of the pigments in the yeasts.

Spoilage under anaerobic condition

Facultative and anaerobic bacteria are able to grow within the meat under anaerobic conditions and cause spoilage. Few are listed below.

• Souring: Meat sourness brought on by microbe-produced formic, acetic, butyric, propionic, and higher fatty acids as well as other organic acids like lactic or succinic. The action of the meat’s own enzymes during aging or ripening, anaerobic bacterial production of fatty acids or lactic acid, or proteolysis without putrefaction, which is caused by facultative or anaerobic bacteria and is occasionally referred to as “stinking sour fermentation” are all possible causes of sourness. By coliform bacteria and Clostridium species on carbohydrates, acid and gas production occurs. Lactic acid bacteria frequently stimulate the development of vacuum-packed meats, particularly those in gastight wrappers.
• Putrefaction: Putrefaction is the term for the breakdown of proteins and is produced by anaerobic microorganisms with the help of harmful chemicals including hydrogen sulfide, mercaptans, indole, skatole, ammonia, and amines. However, facultative bacteria can also contribute to putrefaction or cause it. Putrefaction is often caused by Clostridium spp. Infectious bacteria include Pseudomonas, Proteus, Clostridium, and Alcaligenes putrefy meat and meat products. Gas production frequently occurs together with clostridia-caused putrefaction.

Prevention of Meat from spoilage

1. Asepsis: Asepsis prevents external microbes from entering into the meat. Sanitizing knives used for slaughtering and maintaining the personal cleanliness of food handlers are further asepsis techniques.
2. Canning: Canning is the most popular way to preserve meat. In order to prevent food spoiling, canning involves enclosing meat in a container and boiling it to kill any bacteria. In most cases, canned goods may be kept at room temperature forever without any problems.
3. Vacuum packaging: Oxygen is required for many bacteria to grow. Due to vacuum packaging, the majority of meats have a storage life of roughly 100 days when kept in a refrigerator. Vacuum packing also reduces unsaturated fatty acid oxidation and delays the growth of rancid meat.
4. Drying: Another popular technique for preserving meat is drying. Meat products are dried to eliminate moisture, preventing the growth of bacteria. Products such as jerky, freeze-dried meats, and dry sausages are all examples of dried meats that may be kept at room temperature for extended periods of time without quickly going bad.
5. Irradiation: Irradiation, or radurization, is a pasteurization method accomplished by exposing meat to doses of radiation. In terms of eliminating food-spoilage bacteria, radurization is as effective to heat pasteurization. Meat is irradiated by being exposed to high-energy ionizing radiation, which is either created by electron accelerators or by being exposed to gamma-radiation-emitting materials like cobalt-60 or cesium-137. Irradiated products are virtually identical in character to non-irradiated products, but they have far less microbial contamination. Fresh meat products that have undergone irradiation still need to be refrigerated and packaged to keep them from spoiling, although their time in the refrigerator has been significantly increased.
6. Fermentation: In the meat industry, fermentation is one traditional method of food preservation. Meat undergoes fermentation by having some harmless microorganisms added. The pH of the meat is decreased as a result of the acid produced by these fermenting bacteria, which also prevents the formation of several harmful germs.
7. Curing and smoking: Meat curing and smoking are the oldest methods of meat preservation. Curing is the process of preserving, flavoring, and coloring meats by adding some combination of salt, sugar, nitrite, and/or nitrate. Meat curing are commonly performed in sausages and ham. The product’s characteristic smokey flavor is created during the smoking process, however the amount and kind of smoke employed might vary significantly depending on the cure. Meat that has been smoked has less moisture available on the surface, which inhibits microbial development and prevents from being deteriorated.

Learn More

References

1. https://www.britannica.com/topic/meat
2. https://www.frontiersin.org/articles/10.3389/fnut.2022.1078201/full
3. https://core.ac.uk/reader/234684080
4. https://www.scielo.br/j/cta/a/3ZDMTNLBZ63pGz3DgsbyS7h/?lang=en
5. https://acikders.ankara.edu.tr/pluginfile.php/204156/mod_resource/content/1/FDE412-%287%29%20meat%20spoilage.pdf
6. https://www.ndvsu.org/images/StudyMaterials/VPH/methods_of_preservation_of_meat.pdf
7. https://www.britannica.com/technology/meat-processing/Preservation-and-storage
8. https://nchfp.uga.edu/publications/nchfp/lit_rev/cure_smoke_cure.html