In today's commodity society, shelf life is a term widely used by everyone, especially in the food industry. This is an indicator that can play a key role, because it is the manufacturer's guarantee and commitment to the quality and efficacy of the commodity during the circulation.
The shelf life is mainly determined by four factors, namely, food composition, processing conditions, packaging and storage conditions. These influencing factors have been incorporated into the food safety and quality control system HACCP (Hazard Analysis Critical Control Point). Food is a rather cumbersome system, in which biological, physical, and chemical changes and reactions occur at the same time. These reactions will cause the nutritional value of the food to decline and produce by-products that affect the nature of the food, and even produce toxins. Similar reactions will continue to occur during the preservation process after processing, and the reaction rate at this time depends on the intrinsic properties of the food, packaging type, storage and transportation conditions, etc.
Causes of spoilage and deterioration of cold fresh meat
The main reasons affecting the spoilage of cold fresh meat can be divided into three points
① The proliferation of microorganisms on the surface of the flesh causes the corruption of the flesh.
The main microorganisms are mainly pseudomonas under aerobic conditions, and mainly anaerobic and facultative anaerobic lactic acid bacteria and enterobacteria under vacuum conditions. Most of the bacteria grow on the surface of the meat, and the bacteria on the surface of the meat can decompose protein and other nutrients, so that the surface of the meat becomes sticky, produces odor, and deteriorates in a short period of time.
② Myoglobin in the meat is oxidized and discolored, which affects the appearance and color of the meat.
The color change of meat is controlled by the chemical state of myoglobin and residual hemoglobin. In the process of cold storage, muscle tissue absorbs oxygen in the air, causing changes in the structure of the body's tissues. A few days before storage, myoglobin forms unstable oxygenated myoglobin that makes fresh meat bright red, and gradually forms stable methemoglobin that makes fresh meat dark red (brown).
③The meat quality is spoiled and deteriorated due to the action of enzymes.
High temperature significantly increases the activity of various enzymes in fresh meat and microorganisms, and significantly increases the activity of enzymes secreted by microorganisms around them, which can facilitate various enzymatic reactions and make meat spoilage.
Ways to extend shelf life
Vacuum packaging and modified atmosphere packaging
For fresh meat, vacuum packaging has the following advantages:
(1) Prevent drying out.
The packaging material shields the water vapor to prevent drying and keep the surface of the fresh meat soft.
(2) Prevent oxidation.
When vacuuming, oxygen and air are removed together, and the packaging material is shielded from the atmosphere, so that no oxygen enters the packaging bag and oxidation is completely prevented.
(3) Prevent the loss of meat flavor.
Packaging materials can effectively block the overflow of volatile aromatic substances, and at the same time prevent the transmission of flavors between different products.
(4) Avoid freezing loss.
The packaging material insulates the product from the outside world, so ice formation and air-drying during freezing can minimize losses.
Modified Atmosphere Packaging
Principle of Modified Atmosphere Preservation
The fresh-keeping mechanism of modified atmosphere packaging is to use packaging materials with good barrier properties to protect the food. It refers to filling the packaging with certain ideal gas components, improving the environmental composition in the packaging under certain temperature conditions, inhibiting the growth of microorganisms and preventing enzymes. The spoilage caused by the deterioration can achieve the purpose of preservation and anticorrosion, thereby prolonging the shelf life of the product. The gas used is usually carbon dioxide, oxygen and nitrogen or their various combinations, and each gas has different effects on fresh meat. Generally, the shelf life of fresh meat packaged in air can reach 10 to 14 days.
Advantages of modified atmosphere preservation
Modified atmosphere packaging is one of the most commonly used and effective methods to extend the shelf life of various foods (including chilled meat). Reasonable modified atmosphere packaging can not only ensure the hygienic quality of the meat, extend the shelf life, but also have a good impact on the sensory quality of the chilled meat. The most commonly used gas components for modified atmosphere packaging are mainly carbon dioxide + oxygen + nitrogen.
The use of this mixed gas is mainly considered from the perspective of controlling microbial growth and sensory quality (such as color). The fresh-keeping effect of this type of modified atmosphere packaging on fresh meat mainly depends on the initial bacterial count of the raw meat, the concentration of carbon dioxide, the presence or absence of oxygen in the packaging bag, the permeability of the packaging material, the storage temperature and the gas composition. It inhibits microorganisms by causing changes in the rate of bacterial synthetase and enzyme reactions, as well as affecting carboxylation and deamination reactions. The mixed gas is equipped with a certain proportion of oxygen to maintain the color of fresh meat and inhibit the growth of pathogenic bacteria.
The modified atmosphere packaging system is a closed system. In this system, there are two processes at the same time: one is the physiological serialization process of the product, that is, the respiration process of metabolism; the other is the air permeability of the packaging material that causes the product and the gas in the packaging bag. The exchange process, these two processes make the air conditioning system a dynamic system.
The principle of modified atmosphere packaging can be summarized into two points: ① destroy the environment where microorganisms depend on growth and reproduction; ② can maintain a certain activity of the internal cells of the food and maintain a certain degree of freshness.
There are two main factors influencing food storage, namely aerobic bacteria and oxidation reaction, both of which require oxygen. Therefore, to extend the shelf life, it is necessary to reduce the oxygen content of the environment. Modified atmosphere packaging technology can make up for the deficiencies of vacuum packaging to a certain extent, and further inhibit the corruption of microorganisms.
Precautions for modified atmosphere packaging
(1) The treatment of fresh meat before packaging.
If the pigs are slaughtered and cooled at 0°C-4°C for 24 hours, the acid excretion process will occur after the ATP stops its activity. The nutrition and taste of the chilled meat processed in this way is far better than that of quick-frozen meat and hot fresh meat. In addition, in order to ensure the fresh-keeping effect of modified atmosphere packaging, it is necessary to control the hygienic indicators of fresh meat before packaging to prevent microbial contamination.
(2) Selection of packaging materials.
Modified atmosphere packaging should use packaging materials with good barrier properties to prevent the gas from leaking out of the packaging and at the same time prevent the infiltration of oxygen in the atmosphere. Usually, composite packaging films with PET, PP, PA, PVDC, etc. as the base material are used. The gas barrier properties of plastic films are generally expressed in terms of air permeability coefficient: the smaller the air permeability coefficient, the better the barrier properties. In addition, all packaging materials must have sufficient mechanical strength to enable them to withstand pressure changes during vacuuming. At the same time, the material is required to have a certain degree of stiffness so that the packaging bag can automatically open and inflate.
(3) Control of product storage temperature.
The influence of temperature on the preservation effect comes from two aspects: one is that the temperature directly affects the activities of various microorganisms on the surface of the flesh; the other is that the barrier properties of packaging materials are closely related to temperature. The higher the temperature, the greater the barrier properties of packaging materials. low. Therefore, it is necessary to realize the temperature control in the whole process from product, storage, transportation to sales.
to sum up
The current vacuum packaging technology can inhibit the growth of microorganisms, prevent secondary pollution, slow the rate of fat oxidation, keep the meat clean and extend the shelf life of meat products. If the cold meat is vacuum-packed, it will have a certain effect on preservation, but its color will be purple-red, which is not perfect.
Only modified atmosphere packaging is an ideal way to extend the shelf life of meat products. Modified atmosphere packaging technology to inhibit the growth of microorganisms, thereby extending the shelf life of meat products. Modified atmosphere packaging can not only make the meat bright red, but also can significantly inhibit the growth and reproduction of spoilage microorganisms, ensure the hygienic quality of the meat, and maintain the good sensory quality of fresh meat products, and significantly extend the shelf life
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