Preservation of meat and meat products from microbial spoilage

Meat and its products consist of numerous nutrient content, it serves as an excellent growth medium for all of the microorganisms. Thus, various preservation methods are used to eliminate the growth of spoilage-causing microorganisms and maintaining the nutritional properties of meat. Several techniques have been used to limit the growth of organisms in meat and meat products.

A. Asepsis

• The aseptic condition should be maintained during slaughtering and handling of meat to avoid microbial contamination.
• It can also be maintained by spraying water on animals before slaughter to remove gross dirt.
• Use sterile knives, utensils, clothes, etc. to avoid microbial contamination.

B. Thermal method

1. Heat processing

• Sterilization refers to the heating of meat at temperatures above 100°C in which spoilage-causing microbes in meat are killed.
• Various meat products differ in water content, fat and consistency so these factors are considered during heat processing.

2. Dehydration.

• Dehydration lowers the water activity to prevent the growth of spoilage-causing microbes.
• The meat is dehydrated mainly in two ways:
  • Sun drying of meat chunks as a means of preservation was practiced in ancient days.
  • The mechanical drying process involves the passage of hot air with controlled humidity.
• Dehydrated meat can be stored for few months to a year in air-tight containers without refrigeration.

3. Canning

• Canning is one of the preservation methods that is achieved by thermal sterilization of a product held in hermetically sealed containers.
• The canning of meat involves several steps including preparation of meat, precooking, filling, exhausting, seaming, thermal processing, cooling, and storage.
• The canned meat products have a shelf life of at least two years at ambient temperature.

4. Smoking

• Smoking is an ancient preservation technique, where meat is subjected to smoke, which enhances the sensory and nutritional characteristics of meat products.
• The meat is exposed to smoke from burning wood or any other plant materials to combustion with or without curing. Curing and smoking of meat are closely related.
• Smoke helps in the preservation of meat by dehydrating the meat surface, lowering the surface pH and antioxidant property of smoke constituents.
• Smoking extends the shelf life of meat up to a year or longer without the need for refrigerated conditions.
• Smoking is an effective treatment against pathogenic microorganisms (Staphylococcus aureus, Escherichia coli, Listeria monocytogenes, Salmonella spp., etc.) and it also reduces lipid oxidation.
• Common smoking methods are hot smoking, smoke roasting, and cold smoking.
  • Hot smoking: In this method, the meat will be hot smoked with mild addition of salt to inhibit bacterial growth. Hot smoking is done with temperatures ranges from 60°C to 93°C.
  • Smoke roasting: In this method, the meat with curing will hot smoked at the temperature of about 300°C. Many spices are added to meat for flavor enhancement and also to inhibit bacterial growth.
  • Cold smoking: In this method, the meat after partially or fully cured is usually hung or placed on racks and allowed to smoke for days at an optimum temperatures ranges of 23-48 °C.

C. Non-thermal method

1. Freezing method

• Freezing is the best method for preserving fresh meat as well as keeping the original characteristics of fresh meat by slowing down the enzymatic reactions and growth of microbes.
• A temperature of –55 °C is the ideal temperature for frozen meat to completely prevent quality changes and reduce microbial spoilage.
• The microbial growth will be arrested without killing microbes which slows the spoilage process.
• Uncooked meat such as steaks or chops could be frozen for 4-12 months and the cooked meat can be stored for 2-3 months.

2. Chilling

• This is the most widely used method of preservation for the short-term storage of meat.
• The fresh meat is stored at a refrigeration temperature of 0ºC to 8ºC 
• Generally, fresh meat remains in good condition for a period of 5-7 days if kept at a refrigerated temperature of 4 ± 1°C
• Chilling of meat inhibits the multiplication and metabolic activities of pathogenic bacteria, viruses, and toxins.
• Certain parasites such as Taenia cysts and all stages of Trichinella spiralis might be destroyed by storing infected meat at 18ºC for periods of 20 to 30 days.

3. Freeze-drying

• It is a technology which is using the physical principle called sublimation in which the meat is preserved at low temperatures from –10°C to –25°C.
• The meat will be frozen first and then sublimes to reduce the moisture content as low as 0.5%.
• During this method, the chemical reactions tend to be slow and microorganisms won’t survive at low temperatures.

D. Curing

• Curing of meat has been an old-age technique for the preservation of meat and also gives a desired flavor to the food.
• It preserves the meat by decreasing water activity and by increasing osmotic pressure that delays microbial growth.
• Sodium chloride, sodium nitrite, potassium nitrite, and sugar are the main curing ingredients.
• Curing also involves preserving food items by combinations of salt, nitrates, nitrites, or sugar.
• Salting can be done by rubbing salt on meat or is soaked in brine containing at least 18% salt.
• Sugars bind with moisture and reduce water activity in meat. 20–25% sugar concentration is generally used during curing.
• Dextrose, sucrose, brown sugar, corn syrup, lactose, honey, molasses, maltodextrins, and starches are generally used in meat to enhance flavor, reduce the harshness of salt, and lower water activity.
• Sodium nitrite and potassium nitrite are effective in controlling the growth of anaerobic bacteria, the color of meat, lipid oxidation, and odor.

E. Spices

• Different types of spices are used in meat to impart unique flavors and to extend its shelf-life.
• These include spices like pepper, black pepper cloves, allspice, cinnamon, garlic, onion, anise, etc.
• The spices act as antioxidants by reducing the rate of oxidative rancidity development.
• The spices are used during curing, smoking, cooking which helps to enhance the flavor.

F. Fermentation and pickling

• Fermentation is an ancient process that has been used in the meat industry as a method of preserving meat with enhancement in flavor.
• It is a simple and inexpensive method for the preservation of meat and meat products.
• Meat fermentation is a complex biological process in which desirable microorganisms are used with the addition of spices.
• Lactobacillus is usually used for meat fermentation.
• The acid production, H2O2 production, and antimicrobial agents produced by starter cultures are responsible for preventing the growth of food-borne pathogens and spoilage-causing microorganisms in meat.
• In pickling, meat products are immersed in brine in containers to store the meat.
• The high concentration of salt and spices in pickling acts as a barrier for pathogens and undesirable bacteria.

G. Use of preservatives agents

Preservatives are substances that are capable of inhibiting or retarding the growth of microorganisms. Such preservatives used in food can be divided into three types:

1. Natural preservatives
2. Bio preservatives
3. Chemical preservatives

Some preservatives used in meat and meat products and their effects are:

H. Irradiation

• Ultraviolet (UV) radiation is electromagnetic radiation having a wavelength of about 10-400 nm.
• UV radiations are mostly bactericidal and used for surface sterilization of meat.
• Gamma rays, X-rays, and accelerated electron beams are the sources of ionizing radiation used for the preservation of foods.
• Irradiation, also known as “cold sterilization “affects the microbes by damaging their DNA and ionization of water.

I. Hydrostatic pressure processing

• It is a non – thermal pasteurization process in which food is subjected to high pressure in the region of 3300 -600 Mpa for about 10 minutes.
• High pressure affects the cellular physiology of the microorganisms and it is used as an additional final step during the processing of meat.
• It inhibits the microorganism in meat by interfering with regular cellular functions and inactivate certain food enzymes.

J. Hydrodynamic pressure processing

• Hydrodynamics refers to the motion of fluids and the pressure acting on solid bodies immersed in these fluids.
• It is the concept of tenderizing meat using shock waves from underwater detonation that creates pressure on vacuum-packaged meat in the range of 70 MPa to 100 MPa and reduces the microbes which may be present on meat.

K. Packaging

• Packaging protects products from microbial spoilage and defects such as discoloration, off-flavor and off-odor development, nutrient loss, texture changes, pathogenicity caused by them.
• There are various types of packaging used for meat products for their preservation without deteriorating it’s nutritive and texture.
• Vacuum packaging (VP) is defined as “the packaging of a product in a high barrier package from which air is removed to prevent the growth of aerobic spoilage organisms, shrinkage, oxidation, and color deterioration. In VP, meats are placed in materials such as ethyl vinyl acetate, polyvinylidene chloride. Due to the lack of O2 in packages, the oxidative deteriorative reactions will decrease, and aerobic bacteria growth is reduced.
• Modified Atmosphere Packaging (MAP) for meat requires a barrier of either moisture or gas permeation through packaging materials. The major gases used are N2 (78%), O2 (20.99%), argon (0.94%) and CO2 (0.03%).
• Active packaging (AP) contains specific compounds into packaging systems that maintain or extend product quality and shelf life. It helps in moisture control, odor controllers, flavor enhancement. Antimicrobial packaging is an example of active food packaging in which bactericidal or bacteriostatic agents into the meat.

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