1. Packaging Purpose

Packaging is mainly to ensure the integrity of the product and avoid physical, chemical and microbiological pollution or damage during transportation and sales; increase the beauty of meat products, easy to carry, and easily arouse consumers’ desire to buy; extend the storage period of food, use packaging means to prevent chemical changes and microbial contamination of products.

2. Influence of Environmental Factors on the Quality of Meat Products

The quality of meat products includes the color, aroma, taste and nutritional value of meat products, the shape, weight and hygiene indicators that should be achieved. Meat products are one of the commodities most susceptible to spoilage due to environmental factors.

The entire circulation link of meat products from processing factory to consumption is complex and changeable. Deterioration due to biological, chemical and physical factors. The direct and indirect influence of these factors on the quality of meat products is an important basis for us to design protective packaging for food.

2.1. The effect of light on the quality of meat products

Light promotes the oxidation reaction of fats in meat products to cause oxidative rancidity, causing food discoloration, light-sensitive vitamin damage and protein denaturation. To reduce or avoid the impact of light on food quality. Directly block, absorb or reflect light through packaging to reduce or avoid direct light exposure to food. At the same time, it prevents some factors that are beneficial to the photocatalytic reaction, such as moisture and oxygen, from passing through the packaging material, thereby playing an indirect protective effect.

2.2. The effect of oxygen on the quality of meat products

Oxygen is closely related to the color change of meat products, which will oxidize the fat in meat products. This oxidation also occurs under low temperature conditions. The resulting peroxide not only makes food lose its edible value but also produces odor and toxic substances. Oxygen can also make vitamins and various amino acids in food lose their nutritional value.

2.3. The effect of humidity or moisture on the quality of meat products

Water can promote the reproduction of microorganisms, promote oil oxidation, promote browning and pigment oxidation. Its presence will cause some physical changes in some foods, such as moisture followed by crystallization, making the food dry and hardened or agglomerated. Some foods lose their brittleness and flavor due to moisture absorption. For dry meat products, controlling the environmental humidity is the key to ensure the quality of meat products.

2.4. The effect of temperature on the quality of meat products

The deterioration of food is mainly due to two factors, biological and abiotic, and temperature has a significant impact on these two factors. In order to effectively slow down the adverse effects of temperature on the quality of meat products, the modern food industry adopts food cold chain technology and low temperature protection technology in food circulation, which can prolong the shelf life of meat products.

3. Quality Variation of Packaged Meat Products and Its Control Package

The quality change of food is mainly the change of biological and chemical properties of food. Changes in chemical properties are mainly due to the oxidation of pigments, oils, vitamins and other substances or non-enzymatic browning caused by the participation of reducing sugar reductone, amino acids and proteins. The results of these chemical reactions will lead to changes in the color and flavor of food and the decline of nutritional value, and even produce toxic substances. In addition, the contamination of the packaged food by the odorous components of plastic packaging materials and the changes in the physical properties of the food itself will also lead to changes in food quality.

4. Packaging Technology

4.1. Moisture-proof Packaging

4.1.1. Moisture-proof packaging is used to prevent damage to the product by water vapor in the air.

Materials that are impermeable or impermeable to water vapor are called moisture barrier packaging materials. For moisture barrier packaging, the choice of packaging materials and sealing are two key factors. The moisture permeability of glass, metal and aluminum foil of a certain thickness in moisture barrier packaging materials can be considered as zero. Some composite materials, especially composite materials containing aluminum foil, waxed paper, and polymer composite materials such as HDPE, PP, PVDC, etc., are better moisture barrier packaging materials.

4.1.2. Hygroscopic Material—Desiccant

Commonly used desiccant Silica gel is a commonly used desiccant. The silica gel particles are hard, absorbent, non-toxic and tasteless, and can be used repeatedly. It can also show the moisture content through the color change. The silica gel is soaked in 40% CaCl2 solution and dried to make color-changing silica gel. The silica gel turns red when the moisture content is >40%, and turns blue when dry. In addition to silica gel, there are desiccants such as CaCl2, activated alumina, and molecular sieves.

How to use the desiccant: The desiccant should be fully dried before use, and must be used in conjunction with moisture barrier materials and airtight containers. The packaging of the desiccant should be moisture-permeable, and the use of the desiccant should be marked to prevent accidental ingestion.

4.2. Vacuum Packaging

Vacuum packaging is a typical oxygen removal method. Its basic principle is to make the product and the packaging bag close together and completely exclude air in the sealed chamber. But when it returns to normal atmospheric pressure, the volume of the product shrinks, so that the vacuum of the package becomes lower than the vacuum in the sealed chamber.

Vacuum packaging methods are batch and continuous. Vacuum packaging machine for bag making: It refers to a device that packs the product into a bag-shaped casing, and then evacuates the air in a vacuum chamber, and then heat seals it. The most widely used is the intermittent vacuum packaging machine, but there are also movable type with a conveyor belt in the lower part of the vacuum chamber and a rotary mobile continuous type vacuum packaging machine with two vacuum chambers.

Vacuum stretch packaging: The vacuum stretch packaging machine must use a forming mold, first heat the film, and then use the forming mold to punch into the shape of the container, and then perform vacuum packaging. The film used for stretch packaging is stretch film, which is divided into soft film and hard film. This film has the characteristics of excellent formability, high transparency, oxygen barrier, heat resistance, adhesion, smoothness, anti-fog, easy to open and so on. This film is equipped with a thermoforming packaging machine, which can not only pack solids, liquids, soft objects, fragile items, etc., but also vacuum soft film packaging, hard film inflatable packaging, blister packaging, etc. It is hygienic, efficient, labor-saving and low-cost in use. Products suitable for stretch packaging include block products, sliced ​​products, Frankfurt sausage products, Vienna sausages, etc. This kind of packaging has become the trend of food packaging in the future. At present, 0.25-0.5mm thick plastic sheets (PE, PP, PVC, PS) and a small amount of composite material sheets are mainly used. The cover material is made of PE, PP, KPVC or aluminum box, paper and PE compound, etc. Generally, the trademark and label are printed on the cover material first.

Vacuum body packaging: This type of packaging uses the product instead of the packaging mold, and the packaging shape is the actual shape of the product. This kind of packaging has a good vacuum degree, and can also suppress the juice precipitated from the product, and the preservation effect is better. This type of packaging is available in both continuous and intermittent types and is suitable for packaging ham, bacon, sausages, etc. When packaging irregularly shaped meat products, it can better reflect its advantages.

Advantages of vacuum packaging: Deoxidation has a protective effect on the product; sterilization after vacuum packaging is not easy to break. The disadvantage is that the appearance is not beautiful. Vacuum packaging requires the packaging to have excellent gas barrier properties and certain mechanical strength. Vacuum packaging can be used for braised meat, ham, grain foods, seasonings, etc., but it is unfavorable for foods with high elasticity and porous foods (there are air pockets in the holes). Under vacuum conditions, aerobic spores that are not completely killed during sterilization cannot grow. This type of packaging requires high air tightness and sometimes light protection, so composite materials are used. The most commonly used and effective composite material today is PVDC (polyvinylidene chloride). It has the characteristics of heat shrinkage, high air tightness, softness, and easy sealing. The products packaged with this material can be sterilized by high temperature, and the storage period of the product can be extended to 6-24 months. 4 ℃ can be stored for 4-8 months.

4.3. Modified Atmosphere Packaging

Modified Atmosphere Packaging can be defined as “the technology of regulating the gas environment of food in a material that prevents gas from entering and leaving”.

An important feature of modified atmosphere packaging is to adjust the gas composition within the packaging at the initial storage, inhibiting food spoilage and spoilage, in order to maintain the quality of the food or prolong its shelf life. For example, the air in the bag is drawn out and then filled with N2 or CO2 gas, the purpose of which is to inhibit the growth of anaerobic microorganisms. After vacuum packaging, the packaged items are subject to a certain pressure due to the unbalanced internal and external pressure, which is easy to stick to a block. Crispy and fragile foods such as fried potato chips are easy to be crushed, and irregularly shaped foods are vacuumed. The wrinkled surface is not beautiful, and the food with sharp corners is easy to pierce the packaging bag. The use of modified atmosphere packaging can solve these shortcomings of vacuum packaging, so that the internal and external pressures of the packaging tend to be balanced, thereby protecting the bagged food and the beauty of the packaging. Modified atmosphere packaging is suitable for the packaging of Vienna sausages and frankfurters.

• Nitrogen only plays the role of inert filling, and has no sterilization effect. Nitrogen does not chemically interact with food, nor is it absorbed by food. For foods that are highly susceptible to oxidative deterioration, N2 can replace O2 in them, which can effectively delay the oxidative deterioration of food and preserve food quality.
• The normal content of carbon dioxide CO2 in the air is 0.3%. CO2 can promote the reproduction of many microorganisms at low concentrations, but can hinder the reproduction of microorganisms at high concentrations. When the content of carbon dioxide in the package is 10%-40%, it has an inhibitory effect on microorganisms. When it is more than 40%, it has obvious sterilization effect. In addition, CO2 is easy to form weak acid, which is easy to change the flavor of food.
• Oxygen is generally not used alone as a filling gas, and is often mixed with CO2 and N2 to form an ideal gas for inflatable packaging of fresh food. Its function is to maintain the activity of the cells inside the fresh food, delay its life process, and maintain a certain degree of freshness. Appropriate packaging materials and packaging methods should be used.

4.4. The Use of Deoxidizer Packaging

In a short period of time, the use of organic or inorganic substances to chemically react with oxygen in the packaging ambient air to form irreversibly stable compounds, thereby removing oxygen in the container. Packaging is called packaging technology using deoxidizers. Generally, oxygen should be removed within 24-48h to maintain the oxygen in the bag below a certain limit concentration, prevent fading, oxidation, and inhibit bacterial growth. The advantages of using a deoxidizer for deoxygenation are as follows:

• No special equipment is required, easy to operate, flexible to use, and thoroughly deoxygenated.
• It can overcome the damage of vacuum packaging to food with poor strength, and there is no mechanical impact.
• For foods that are soft and cannot be vacuumed, it can effectively remove O2.
• Deoxidizers can slowly absorb O2 and permanently deoxidize.

At present, most of the deoxidizers on the market are packed in powder bags. There are pills or other forms abroad, made into paste or liquid. Or immerse a highly permeable material (such as a foam or paper) in a deoxidizer, and after losing moisture, the active material will remain on the material. When applying flake, granular or powder deoxidizers, it should be noted that the food packaging materials using deoxidizers must be high oxygen barrier materials (PVA, EVOH, PVDC), and the packaging space should be minimized to save deoxidizers. When using a deoxidizer, a certain temperature and humidity are required. In particular, the temperature conditions are strict and generally cannot be frozen. Freezing will deactivate the deoxidizer, and the deactivation caused by low temperature is irreversible. Therefore, it is generally not used in frozen foods.

Deoxidizers are generally divided into catalyst type, inorganic type, organic type and photosensitive type. Commonly used deoxidizers include hydrogenation catalyst type (platinum, palladium, rhodium), organic deoxidizers (such as glucose and ascorbic acid, etc.), iron-based deoxidizers and dithionite-based deoxidizers. In addition to the above deoxidizers, new deoxidizers, such as photosensitive deoxidizers, have been developed in recent years.

4.5. Heat Shrink Wrap

The method of wrapping a product or package with a heat-shrinkable plastic film, and then heating it to a certain temperature to make the film shrink and wrap around the product or package is called heat-shrinkable packaging. The main features of heat shrink packaging are as follows:

• It can adapt to the packaging of items of various sizes and shapes.
• It can achieve sealed, moisture-proof and fresh-keeping packaging for food, and has good product protection.
• Using the shrinkage of the film, collective packaging can be implemented. It is beneficial to self-selection and supermarket sales, and reduces collisions and avoids damage.
• In addition to the protective effect, the transparent packaging film also increases the appearance gloss, improves the appearance decoration effect and promotion function of the product.
• The packaging is compact, convenient for storage and transportation, the packaging material is light and less used, and the packaging cost is low.
• The packaging process and equipment are simple, and the versatility is strong, which facilitates the realization of mechanized packaging operations, and the packaging strength is low. Commonly used shrink film materials are Pvc.PE, PP, and pvpc, PS.EVA and foamed PE, PS.