Preservation of meat and meat products from microbial spoilage

Asepsis is the state of being free from disease-causing microorganisms. Maintaining aseptic conditions during slaughtering and handling of meat is essential to avoid microbial contamination and spoilage of meat products. Aseptic processing is a technique that involves placing a sterilized product into a sterilized package that is then sealed under sterile conditions . Some of the methods to achieve asepsis in meat processing are:

• Spraying water on animals before slaughter to remove gross dirt and reduce the microbial load on the skin.
• Using sterile knives, utensils, clothes, gloves, and other equipment to avoid introducing microbes from the environment or the handlers.
• Cleaning and sanitizing the equipment and surfaces that come in contact with meat frequently and thoroughly.
• Separating raw and cooked meat to prevent cross-contamination.
• Using high-temperature–short-time (HTST) method to heat the meat at a high temperature for a short period of time to kill spoilage-causing microbes. The time and temperature conditions depend on several factors, such as size, shape, and type of meat.
• Using heat exchangers, such as tubular, plate, or scraped-surface types, to transfer heat efficiently and uniformly to the meat product.
• Using ohmic heating, which involves passing electric current through the meat product to generate heat internally and uniformly.
• Using packaging materials and equipment that are sterilized with various medium or combination of mediums, such as saturated steam, superheated steam, hydrogen peroxide and heat, or other treatments .
• Sealing the packages under sterile conditions to prevent recontamination of the product .
• Storing and transporting the packages at appropriate temperatures to maintain the quality and safety of the product .

Aseptic processing and packaging can extend the shelf life of meat products for several months or years without refrigeration. It can also preserve the nutritional and sensory characteristics of meat products better than conventional methods. However, it requires strict quality control and monitoring to ensure that all the steps are performed correctly and effectively. Any deviation from the scheduled process can compromise the sterility of the product and pose a risk of foodborne illness. Therefore, aseptic processing and packaging should be done by trained personnel following standard operating procedures and good manufacturing practices.

Using heat processing, dehydration, canning, and smoking to preserve meat.

Heat processing

Heat processing is a method of preserving meat by heating it at temperatures above 100°C, which kills spoilage-causing microbes and inactivates enzymes. The heat processing can be done by sterilization or pasteurization.

• Sterilization refers to heating the meat at temperatures above 121°C for a specified time, which destroys all microorganisms and spores. Sterilized meat products can be stored for a long time at ambient temperature without refrigeration. However, sterilization may cause undesirable changes in the color, flavor, texture, and nutritional value of the meat.
• Pasteurization refers to heating the meat at temperatures below 100°C for a short time, which reduces the number of pathogenic and spoilage microorganisms but does not eliminate them completely. Pasteurized meat products have a longer shelf life than fresh meat but still require refrigeration. Pasteurization preserves most of the sensory and nutritional qualities of the meat.

Dehydration

Dehydration is a method of preserving meat by reducing its water content, which lowers the water activity and prevents the growth of microorganisms. The dehydration can be done by sun drying or mechanical drying.

• Sun drying is an ancient method of preserving meat by exposing it to direct sunlight, which evaporates the moisture and also provides some antimicrobial effects from UV radiation. Sun drying is a simple and inexpensive method but depends on climatic conditions and may result in uneven drying, contamination, and insect infestation.
• Mechanical drying is a modern method of preserving meat by passing hot air with controlled humidity over the meat, which removes the moisture uniformly and rapidly. Mechanical drying is more efficient and hygienic than sun drying but requires energy and equipment. Mechanical drying can be done by hot air oven drying, spray drying, drum drying, or freeze drying.

Canning

Canning is a method of preserving meat by sealing it in hermetically closed containers and subjecting it to thermal processing, which makes it sterile and shelf-stable. The canning process involves several steps:

• Preparation of meat: The meat is cleaned, trimmed, cut, seasoned, and precooked as required.
• Filling: The meat is filled into suitable containers such as cans, glass jars, pouches, or trays.
• Exhausting: The air is removed from the containers by vacuum or steam to prevent oxidation and swelling during thermal processing.
• Seaming: The containers are sealed with lids or closures to make them airtight.
• Thermal processing: The containers are heated in water or steam at a specified temperature and time combination to achieve sterilization or pasteurization.
• Cooling: The containers are cooled rapidly in water or air to stop the cooking process and prevent overcooking.
• Storage: The containers are labeled, coded, inspected, and stored under proper conditions.

Smoking

Smoking is an ancient method of preserving meat by exposing it to smoke from burning wood or other plant materials, which enhances the sensory and nutritional characteristics of the meat products. Smoking preserves the meat by dehydrating the surface, lowering the pH, and providing antioxidant and antimicrobial effects from smoke constituents. Smoking can be done by hot smoking, smoke roasting, or cold smoking.

• Hot smoking: In this method, the meat is cured with salt or brine and then smoked at temperatures ranging from 60°C to 93°C for a few hours. Hot smoking cooks the meat and gives it a smoky flavor and color. Hot smoked meat products have a short shelf life and require refrigeration.
• Smoke roasting: In this method, the meat is cured with salt or brine and spices and then smoked at temperatures above 100°C for several hours. Smoke roasting cooks the meat thoroughly and gives it a roasted flavor and color. Smoke roasted meat products have a longer shelf life than hot smoked products but still require refrigeration.
• Cold smoking: In this method, the meat is fully cured with salt or brine and spices and then smoked at temperatures below 30°C for several days. Cold smoking does not cook the meat but gives it a mild smoky flavor and color. Cold smoked meat products have a long shelf life and can be stored without refrigeration.

Non-thermal methods are food preservation techniques that do not involve the application of heat to the food products. They are preferred over thermal methods because they can retain the fresh-like quality, nutritional value, and sensory attributes of food products, while ensuring food safety and extending shelf life. Some of the non-thermal methods used for meat preservation are:

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.

1. Chilling method

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.

1. Freeze-drying method

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. Freeze-dried meat products have a long shelf life, light weight, and high rehydration capacity.

Other non-thermal methods that are not commonly used for meat preservation but have potential applications are:

• High pressure processing (HPP): 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.
• Pulsed electric field (PEF): It is a technique that uses short pulses of high voltage electric fields to induce pores in the cell membranes of microorganisms, leading to their inactivation. PEF can be applied to liquid or semi-solid foods, such as marinated meats, sausages, or minced meats.
• Ultraviolet (UV) light: It is electromagnetic radiation having a wavelength of about 10-400 nm. UV radiations are mostly bactericidal and used for surface sterilization of meat. UV light can also be used to generate ozone, which is a strong oxidizing agent that can kill microorganisms and degrade organic pollutants.
• Irradiation: It is a technique that uses gamma rays, X-rays, or accelerated electron beams to induce ionization of water and other molecules in food, resulting in DNA damage and cell death of microorganisms. Irradiation can also reduce lipid oxidation, improve color stability, and increase shelf life of meat products.
• Ultrasound: It is a technique that uses sound waves with frequencies above 20 kHz to generate cavitation, shock waves, and shear forces that can disrupt cell membranes and kill microorganisms. Ultrasound can also enhance mass transfer, tenderization, emulsification, and extraction processes in meat products.

Curing of meat is an ancient technique of preserving meat by reducing its water activity and increasing its osmotic pressure, which inhibits the growth of spoilage-causing microorganisms . Curing also enhances the flavor, color, and texture of meat products . Curing can be done by using salt, sugar, nitrates, nitrites, spices, acidity, or smoke .

There are different methods of curing meat, such as:

• Dry curing: This method involves rubbing salt and other curing ingredients on the surface of the meat and letting it rest for a period of time, usually in a cool and dry place . The salt draws out moisture from the meat and creates a hostile environment for bacteria . Some examples of dry-cured meats are prosciutto, pancetta, bresaola, and salami .
• Equilibrium curing: This method involves weighing the meat and calculating the exact amount of salt and other curing ingredients needed to achieve a desired salt concentration in the final product. The curing mixture is then applied to the meat and vacuum-sealed in a plastic bag. The meat is refrigerated for a period of time until the salt and other ingredients are evenly distributed throughout the meat. This method allows for more precise control over the saltiness and moisture content of the cured meat.
• Brine curing: This method involves submerging the meat in a liquid solution of salt, water, and other curing ingredients . The brine penetrates the meat by diffusion and osmosis and preserves it by lowering its water activity and pH . Brine curing can also be done by injecting the brine into the meat using a syringe or a pump . Some examples of brine-cured meats are ham, bacon, corned beef, and pastrami .
• Combination curing: This method involves injecting the meat with a brine solution and then applying a dry rub of salt and other curing ingredients on the surface of the meat . The combination of brine injection and dry rub ensures that the curing agents reach both the interior and exterior of the meat . This method can speed up the curing process and prevent spoilage .

Some common curing ingredients are:

• Salt: Salt is the most essential ingredient in curing as it preserves the meat by dehydrating it, lowering its pH, inhibiting bacterial growth, and enhancing flavor. Salt can be either sea salt or kosher salt. Table salt is not recommended as it may contain additives that can affect the quality of the cured meat.
• Sugar: Sugar is often added to curing mixtures to balance the saltiness, add sweetness, improve browning, and lower water activity. Sugar can be in various forms such as sucrose, dextrose, lactose, honey, molasses, or corn syrup.
• Nitrates and nitrites: Nitrates and nitrites are compounds that prevent the growth of Clostridium botulinum, a bacterium that can cause botulism, a deadly form of food poisoning. Nitrates and nitrites also help to develop the characteristic pink color and cured flavor of some meats by reacting with myoglobin, a protein that carries oxygen in muscle tissue. Nitrates and nitrites can be either natural (from celery juice or powder) or synthetic (from sodium nitrate or sodium nitrite). Synthetic nitrates and nitrites are often sold as "curing salt", "pink salt", or "Prague powder" and should be used with caution as they can be toxic in high doses.
• Spices: Spices are added to curing mixtures to impart unique flavors and aromas to the cured meat. Spices can also have antimicrobial and antioxidant properties that can enhance the shelf life and quality of the cured meat. Some common spices used in curing are black pepper, garlic, onion, paprika, bay leaf, thyme, rosemary, juniper, coriander, fennel, and cumin.
• Acidity: Acidity is another factor that can affect the preservation and flavor of cured meat. Acidity can be introduced by adding vinegar, lemon juice, wine, or cultured bacteria to the curing mixture. Acidity can lower the pH of the meat, inhibit bacterial growth, enhance color development, and create a tangy taste.
• Smoke: Smoke is not a necessary ingredient for curing, but it can add another layer of flavor and protection to the cured meat. Smoke can be generated by burning wood or other plant materials and exposing the meat to the smoke for a period of time. Smoke can dehydrate the meat surface, lower the surface pH, and provide antioxidant and antimicrobial compounds that can prevent spoilage and rancidity. Some examples of smoked meats are smoked ham, smoked bacon, smoked salmon, and smoked turkey.

Curing meat is a rewarding and satisfying way to preserve and enjoy meat. By following the proper methods and ingredients, you can create your own delicious cured meats at home.

Spices are aromatic or pungent plant substances that are used to flavor or preserve food. Spices have been used for centuries as natural food preservatives, especially for meat and meat products. Spices can inhibit or retard the growth of microorganisms in meat by various mechanisms, such as:

• Reducing the water activity and increasing the osmotic pressure of the meat, which prevents the microbial growth and metabolism.
• Acting as antioxidants, which prevent the oxidative rancidity and deterioration of meat quality.
• Producing antimicrobial compounds, such as essential oils, phenolic compounds, allicin, etc., which interfere with the cell membrane, enzyme activity, or DNA of the microorganisms.

Some of the common spices that are used for meat preservation are:

• Salt: Salt is one of the oldest and most widely used spices for preserving meat. Salt draws out the moisture from the meat, creating an unfavorable environment for microbial growth. Salt also enhances the flavor and texture of the meat. Salt can be applied to meat by rubbing, soaking in brine, or injecting into the muscle tissue. Salt-cured meat can last for several months without refrigeration .
• Black pepper: Black pepper is a spice that has antimicrobial, antifungal, and prebiotic properties. Black pepper contains an active compound called piperine, which inhibits the growth of bacteria, fungi, and molds. Black pepper also stimulates the production of digestive enzymes and beneficial bacteria in the gut, which improve the digestion and immunity of the consumer. Black pepper can be added to meat during curing, smoking, cooking, or marinating .
• Cumin: Cumin is a spice that has antibacterial, antifungal, antioxidant, and anti-inflammatory properties. Cumin contains an essential oil that has a strong inhibitory effect on various pathogens, such as Staphylococcus aureus, Escherichia coli, Salmonella typhimurium, etc. Cumin also scavenges free radicals and reduces lipid peroxidation in meat. Cumin can be used to season meat during curing, cooking, or fermenting .
• Mustard seeds: Mustard seeds are spices that have antimicrobial, antifungal, antioxidant, and anti-carcinogenic properties. Mustard seeds contain glucosinolates, which are converted into isothiocyanates by an enzyme called myrosinase when crushed or chewed. Isothiocyanates are potent antimicrobial agents that disrupt the cell membrane and enzyme activity of microorganisms. Mustard seeds also contain phenolic compounds that act as antioxidants and prevent oxidative damage to meat. Mustard seeds can be used to make mustard paste or powder, which can be applied to meat during curing, smoking, cooking, or pickling .
• Ginger: Ginger is a spice that has antibacterial, antifungal, antioxidant, anti-inflammatory, and anti-nausea properties. Ginger contains gingerols and shogaols, which are phenolic compounds that have a broad-spectrum antimicrobial activity against bacteria, fungi, and viruses. Ginger also contains zingerone and paradol, which are antioxidants that prevent lipid oxidation and rancidity in meat. Ginger can be used to make ginger paste or powder, which can be added to meat during curing, cooking, or marinating .

Other spices that can be used for meat preservation include garlic, onion, clove, cinnamon, allspice, anise, turmeric, coriander, cardamom, nutmeg, etc. Spices not only preserve meat but also impart unique flavors and aromas to it. Spices can also enhance the nutritional value and health benefits of meat by providing phytochemicals, vitamins, minerals, and dietary fiber.

Fermentation and pickling are two methods of preserving meat with enhancement in flavor. They are often confused, but they have some key differences.

Fermentation is a process in which desirable microorganisms are used to convert the sugars and carbohydrates in meat into acids, alcohols, gases, and other compounds. The most common type of fermentation for meat is lactic acid fermentation, in which lactobacillus bacteria produce lactic acid that lowers the pH and inhibits the growth of spoilage-causing and pathogenic microorganisms. Fermentation also produces probiotics, enzymes, vitamins, and other beneficial substances that improve the nutritional and health value of meat.

Fermentation does not require an added acidic liquid or heat, and can be accomplished with as little as a container, salt, water, and spices. The meat is submerged in a brine solution that varies from one fermented product to another, depending on the type of meat, the desired flavor, and the local traditions. The fermentation process typically takes longer than pickling and ultimately alters the meat`s color, flavor, texture, and aroma.

Some examples of fermented meat products are:

• Salami: A type of dry-cured sausage that is fermented by lactic acid bacteria and mold cultures. Salami has a distinctive tangy flavor and a firm texture.
• Kimchi: A traditional Korean dish made from various vegetables and seasonings that are fermented with lactic acid bacteria. Kimchi can also include meat, such as pork or seafood, to add protein and flavor.
• Sauerkraut: A German dish made from shredded cabbage that is fermented with lactic acid bacteria. Sauerkraut can be eaten as a side dish or used as a topping for sausages, sandwiches, or salads.
• Corned beef: A type of salt-cured beef that is fermented with lactic acid bacteria and spices. Corned beef is usually cooked by boiling or steaming and served with cabbage, potatoes, or bread.

Pickling is a process of preserving meat by immersing it in an acidic solution, usually vinegar, or in salt solution (brine). In the latter case, the acid that does the preservative action (lactic acid mainly) is produced by fermentation. The process of pickling is also known as brining and the resulting meats as pickles.

Pickling involves the use of heat, which serves to destroy and inhibit the growth of any microorganisms. The acidic solution also changes both the taste and texture of the meat. Pickling usually requires less time than fermentation and preserves the meat`s original color more than fermentation does.

Some examples of pickled meat products are:

• Pickled herring: A type of preserved fish that is cured with salt and then soaked in vinegar or brine with spices and sugar. Pickled herring has a sour and sweet flavor and a soft texture.
• Pickled eggs: A type of preserved egg that is boiled, peeled, and then soaked in vinegar or brine with spices and herbs. Pickled eggs have a tangy flavor and a firm texture.
• Pickled pork: A type of preserved pork that is cooked in vinegar or brine with spices and sugar. Pickled pork has a sour and sweet flavor and a tender texture.
• Pickled tongue: A type of preserved beef tongue that is cooked in vinegar or brine with spices and sugar. Pickled tongue has a sour and sweet flavor and a soft texture.

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

• Natural preservatives
• Bio preservatives
• Chemical preservatives

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

• Salt: Salt is one of the oldest and most widely used preservatives for meat. It lowers the water activity and creates an osmotic pressure that prevents the growth of most bacteria. Salt also enhances the flavor and texture of meat. However, excessive salt intake can cause health problems such as hypertension and cardiovascular diseases.
• Sugar: Sugar is another common preservative that reduces the water activity and inhibits microbial growth. Sugar also improves the palatability and color of meat products. However, too much sugar can increase the risk of obesity and diabetes.
• Vinegar: Vinegar is a natural acidulant that lowers the pH and inhibits the growth of spoilage and pathogenic bacteria. Vinegar also adds a sour taste and aroma to meat products. Vinegar can be used alone or in combination with salt, sugar, and spices for pickling meat.
• Spices: Spices are plant-derived substances that have antimicrobial, antioxidant, and flavoring properties. Spices such as pepper, cloves, cinnamon, garlic, onion, etc. can inhibit or delay the growth of bacteria, fungi, and molds in meat. Spices also scavenge free radicals and prevent lipid oxidation in meat products.
• Lactic acid bacteria: Lactic acid bacteria are bio preservatives that produce lactic acid and other antimicrobial compounds such as bacteriocins, hydrogen peroxide, and diacetyl. Lactic acid bacteria can ferment sugars and lower the pH of meat products, which inhibits the growth of spoilage and pathogenic microorganisms. Lactic acid bacteria also improve the flavor, texture, and safety of fermented meat products such as salami, ham, sausage, etc.
• Nitrates and nitrites: Nitrates and nitrites are chemical preservatives that are added to cured meat products to prevent the growth of Clostridium botulinum, which causes botulism. Nitrates and nitrites also stabilize the color of meat by forming nitrosomyoglobin, which gives a pink hue to cured meat. However, nitrates and nitrites can react with amines in meat to form nitrosamines, which are carcinogenic compounds.
• Sorbic acid and sorbates: Sorbic acid and sorbates are chemical preservatives that inhibit the growth of yeasts and molds in meat products. Sorbic acid and sorbates are effective at low pH and have a minimal effect on the flavor and color of meat products. However, some people may be allergic or sensitive to sorbic acid and sorbates.
• Benzoic acid and benzoates: Benzoic acid and benzoates are chemical preservatives that inhibit the growth of yeasts, molds, and some bacteria in meat products. Benzoic acid and benzoates are effective at low pH and have a slight acidic taste. However, some people may be allergic or sensitive to benzoic acid and benzoates.
• Propionic acid and propionates: Propionic acid and propionates are chemical preservatives that inhibit the growth of molds and some bacteria in meat products. Propionic acid and propionates are effective at low pH and have a slight sour taste. However, some people may be allergic or sensitive to propionic acid and propionates.

The use of preservative agents in meat products can extend their shelf life and prevent microbial spoilage. However, some preservative agents may have adverse effects on human health or cause allergic reactions in some individuals. Therefore, it is important to use them at appropriate levels and follow the regulations for their use in food products.

Irradiation is a food safety process that uses radiation to kill germs that can cause food poisoning (foodborne illness) in meat and meat products. It also extends the shelf life and quality of products by delaying spoilage and reducing the growth of microorganisms .

Irradiation works by exposing food products to ionizing radiation, such as gamma rays, X-rays, or electron beams. The radiation penetrates the food and damages the DNA of the microorganisms, preventing them from multiplying or surviving. The irradiation process happens after a food is produced and packaged, and does not make the food radioactive.

The Food and Drug Administration (FDA) has approved irradiation for use on various foods, including fresh and frozen red meat, poultry, eggs, spices, fruits, and vegetables. The FDA determines the safe and effective doses of radiation for each type of food. For meat and poultry, the approved doses range from 1.5 to 7 kilograys (kGy), depending on the product and the intended effect.

Irradiation has several benefits for meat preservation, such as:

• Prevention of foodborne illness: Irradiation can effectively eliminate organisms that cause foodborne illness, such as Salmonella, Escherichia coli (E. coli), Campylobacter, and Listeria monocytogenes .
• Preservation: Irradiation can destroy or inactivate organisms that cause spoilage and decomposition and extend the shelf life of foods. For example, irradiation can increase the shelf life of refrigerated beef from 2-3 weeks to 4-6 weeks.
• Control of insects: Irradiation can destroy insects in or on meat products imported into the United States. Irradiation also decreases the need for other pest-control practices that may harm the product.
• Sterilization: Irradiation can be used to sterilize foods, which can then be stored for years without refrigeration. Sterilized foods are useful in hospitals for patients with severely impaired immune systems, such as patients with AIDS or undergoing chemotherapy. Foods that are sterilized by irradiation are exposed to substantially higher levels of treatment than those approved for general use.

Irradiation does not affect the sensory characteristics of meats, including color, taste, and texture, as long as the appropriate dose is used. However, its influence on the chemical and nutritional aspects of meat is complex as it can alter amino acids, fatty acids, and vitamins as well as generate free radicals that cause lipid oxidation. These changes are usually minor and comparable to those caused by other preservation methods such as cooking, freezing, canning, and smoking .

Irradiated foods are safe to eat and do not pose any health risks to consumers. The FDA has evaluated the safety of irradiated food for more than 30 years and has found the process to be safe. The safety and efficacy of irradiation have also been endorsed by various federal agencies and intergovernmental organizations such as the U.S. Department of Agriculture (USDA), the Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO), and the Food and Agriculture Organization (FAO) of the United Nations.

Consumers can identify irradiated foods by looking for two symbols: the Radura logo and a statement that indicates that the product has been treated with irradiation. The Radura logo is a green circle with a stylized plant inside surrounded by broken lines representing radiation. The statement may say "treated with radiation" or "treated by irradiation" or use an alternative wording approved by the FDA. These symbols are required on packaged foods that have been irradiated as well as on bulk containers of irradiated foods sold to retailers or food service establishments. However, these symbols are not required on individual servings of irradiated foods sold in restaurants or other prepared food outlets.

Irradiation is one of the many preservation technologies available for meat and meat products. It is not a substitute for good sanitation and process control in meat plants. It is an added layer of safety that can help prevent foodborne disease and enhance food quality.

Hydrostatic pressure processing (HPP) is a non-thermal pasteurization method that uses high pressure to inactivate microorganisms and enzymes in food products. HPP can be applied to meat and meat products to extend their shelf life, improve their safety, and modify their texture and color.

HPP involves placing the food product in a flexible package or container and subjecting it to high pressure (usually between 300 and 600 MPa) for a few minutes in a water-filled chamber. The pressure is applied uniformly and instantaneously, without affecting the shape or volume of the food. The temperature increase during HPP is minimal (about 3°C per 100 MPa), so the nutritional and sensory qualities of the food are preserved.

HPP affects the cellular physiology of microorganisms by disrupting their membranes, cell walls, ribosomes, and DNA. It also inactivates some enzymes that are involved in spoilage or quality deterioration, such as proteases, lipases, and oxidases. HPP can reduce or eliminate pathogens such as Listeria monocytogenes, Salmonella spp., Escherichia coli O157:H7, Campylobacter jejuni, and Clostridium botulinum in meat products . HPP can also extend the shelf life of meat products by inhibiting the growth of spoilage bacteria, such as Pseudomonas spp., Brochothrix thermosphacta, Lactobacillus spp., and Enterobacteriaceae .

HPP also affects the structure and function of meat proteins, especially myofibrillar proteins, which are responsible for the texture and water-holding capacity of meat. HPP can induce protein denaturation, aggregation, gelation, and solubilization depending on the pressure level, temperature, time, pH, salt concentration, and muscle type . These changes can result in different effects on the texture and color of meat products.

HPP can be used to tenderize meat by disrupting the myofibrillar structure and weakening the connective tissue. This can improve the juiciness, tenderness, and chewiness of meat products . HPP can also be used to form gels or emulsions from meat proteins by enhancing their solubility and functionality . This can improve the firmness, cohesiveness, elasticity, and stability of processed meat products such as sausages, ham, or pâté .

HPP can affect the color of meat products by altering the oxidation state and stability of myoglobin, the main pigment in meat. HPP can cause a shift from red oxymyoglobin to brown metmyoglobin or pink nitrosomyoglobin depending on the presence of oxygen or nitrite in the package . HPP can also affect the color stability of meat products during storage by influencing lipid oxidation and microbial growth .

HPP is a promising technology for meat preservation and processing that can offer several advantages over conventional thermal methods. However, there are some challenges and limitations that need to be overcome for its wider application in the meat industry. These include:

• The high cost of equipment and maintenance
• The limited availability of suitable packaging materials
• The possible loss of some volatile compounds or nutrients
• The possible formation of off-flavors or undesirable compounds
• The possible variation in quality depending on the raw material characteristics
• The possible need for additional treatments or additives to ensure safety or quality
• The possible consumer perception or acceptance issues

Therefore, further research and development are needed to optimize the process parameters, evaluate the effects on different types of meat products, identify the optimal packaging materials and conditions, assess the sensory and nutritional impacts, ensure the regulatory compliance, and educate the consumers about the benefits of HPP .

Hydrodynamic pressure processing (HDP) is a novel technique for tenderizing meat using shock waves from underwater detonation of explosives. The shock waves create high pressure on vacuum-packaged meat in the range of 70 MPa to 100 MPa and reduce the microbes that may be present on meat .

HDP has been shown to improve cooked meat tenderness by 25% compared to non-treated control samples. HDP also enhances the water-holding capacity, color stability, and sensory attributes of meat. HDP can be applied to beef, pork, and lamb without affecting their appearance or texture .

HDP can also improve the marination and cooking properties of meat by increasing the penetration and retention of marinade ingredients. HDP-treated meat absorbs more marinade and loses less weight during cooking than non-treated meat. HDP can also reduce the cooking time and energy consumption by 10% to 15%.

HDP is a non-thermal process that does not affect the nutritional value or flavor of meat. HDP can also reduce the microbial load of meat by inactivating some food-borne pathogens such as Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes . However, HDP alone may not be sufficient to ensure the safety of meat products, and it may need to be combined with other antimicrobial interventions such as irradiation, high-pressure processing, or natural preservatives .

HDP is a promising technology for meat preservation and quality improvement, but it also faces some challenges and limitations. HDP requires specialized equipment and trained personnel to handle explosives safely. HDP may also generate environmental concerns due to the noise and water pollution caused by underwater detonation. HDP may also affect the shelf life of meat products by increasing lipid oxidation and microbial spoilage during storage .

Therefore, more research is needed to optimize the HDP parameters, evaluate the effects of HDP on different types of meat products, and develop strategies to overcome the drawbacks of HDP. HDP has the potential to become a viable alternative or supplement to conventional methods of meat preservation and tenderization.

Packaging is an essential step in the preservation of meat and meat products, as it protects them from microbial spoilage and other quality defects such as discoloration, off-flavor, off-odor, nutrient loss, and texture changes. Packaging also provides information to consumers about the product characteristics, ingredients, shelf life, storage conditions, and safety aspects.

There are various types of packaging materials and methods used for meat products, depending on their physical, chemical, and microbiological properties. Some of the common packaging methods are:

• Vacuum packaging (VP): This method involves the removal of air from the package before sealing it with a high barrier material such as ethyl vinyl acetate or polyvinylidene chloride. VP reduces the oxygen availability and prevents the growth of aerobic spoilage organisms, shrinkage, oxidation, and color deterioration. VP can extend the shelf life of fresh meat up to 4 weeks at refrigeration temperature (4 ± 1°C) and up to 12 months at freezing temperature (-18°C).
• Modified atmosphere packaging (MAP): This method involves the replacement of air in the package with a gas mixture that is optimal for the preservation of meat quality and safety. The major gases used are nitrogen (N2), oxygen (O2), carbon dioxide (CO2), and argon (Ar). The gas composition depends on the type of meat product, as different meats have different oxygen requirements and sensitivities to CO2. MAP can inhibit the growth of aerobic and anaerobic bacteria, delay oxidative rancidity, and maintain color stability. MAP can extend the shelf life of fresh meat up to 6 weeks at refrigeration temperature and up to 18 months at freezing temperature.

• Active packaging (AP): This method involves the incorporation of specific compounds or agents into the packaging system that can interact with the product or the environment to maintain or extend its quality and shelf life. Some examples of AP are:

  • Antimicrobial packaging: This packaging contains bactericidal or bacteriostatic agents that can inhibit or retard the growth of microorganisms in meat. The agents can be incorporated into the packaging material or coated on its surface. Some examples of antimicrobial agents are organic acids, enzymes, bacteriocins, essential oils, silver nanoparticles, etc.
  • Oxygen scavenging packaging: This packaging contains substances that can remove oxygen from the package headspace or from the product itself. This can prevent oxidative deterioration and microbial spoilage of meat. Some examples of oxygen scavengers are iron-based compounds, ascorbic acid, enzymes, etc.
  • Moisture control packaging: This packaging contains substances that can absorb or release moisture to maintain a desirable water activity in meat. This can prevent dehydration or microbial growth due to excess moisture. Some examples of moisture control agents are silica gel, calcium chloride, starches, etc.

• Irradiation: This method involves the exposure of meat products to ionizing radiation such as gamma rays, X-rays, or electron beams. Irradiation can destroy microorganisms and parasites in meat by damaging their DNA and cell membranes. It can also delay enzymatic reactions and lipid oxidation in meat. Irradiation can extend the shelf life of fresh meat up to 3 weeks at refrigeration temperature and up to 3 years at freezing temperature.

The choice of packaging method for meat products depends on several factors such as product characteristics, consumer preferences, cost-effectiveness, environmental impact, and regulatory requirements. Packaging plays a vital role in ensuring the quality and safety of meat products throughout their shelf life.

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