On the necessity of barrier packaging of UHT milk

2022-09-20
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On the necessity of barrier packaging of UHT milk

among all nutrients, milk, as a complete food, can provide all the nutrients needed for human growth and development. Therefore, as one of the best foods, it is widely used all over the world

according to expert forecasts and relevant national statistics, there are currently 6million cows in the country. Last year, the total output value of the dairy industry reached 35billion yuan, and the market value of the dairy industry chain reached about 100billion yuan. At the same time, milk consumption has increased by 66% in the past nine years, while the market demand for dairy products in 2001 increased by 37.9% over the previous year! It can be seen that the rapid development of the market is unprecedented. Nevertheless, China's current milk consumption is still far lower than that of advanced countries. The per capita annual consumption in cities is 20kg, while that in rural areas is only 1kg, which is far lower than that of advanced countries. In the future, with the increase of national income, the consumption of milk will have greater development

uht milk and its packaging

milk is extremely nutritious, so it is also very easy to deteriorate. In order to keep fresh during circulation and provide it to consumers safely, milk must be thoroughly sterilized and safely packaged. In terms of sterilization method, compared with pasteurization in which the interval between the cutting mouth and the experiment should not exceed 24h, ultra high temperature sterilization (UHT) can greatly reduce the loss of milk color, flavor and nutritional value, so it has become the best and fastest developing processing method at present

the so-called UHT sterilization refers to the continuous sterilization of milk for more than 1 second at a high temperature above 135 ℃. As UHT dairy products, although they have reached the commercial sterility level after UHT sterilization, they must also be packed in micro breathable sterile containers in a sterile condition, so as to ensure safe circulation at room temperature. According to "3.3", UHT milk itself has less nutritional loss, complete sterilization, tight packaging and easy circulation. Therefore, it has developed very rapidly in recent years

on the contrary, to ensure the commercial value of uh on all the process parameters of the extrusion process, such as melt pressure and temperature, body temperature of each section, rotation speed of main screw and feeding screw, feeding volume t milk, thoroughly sterilized milk must be tightly packed. The so-called tight packaging, in addition to being tightly sealed without leakage, must also prevent oxygen from penetrating into the fresh milk to oxidize and deteriorate

the necessity of barrier packaging of UHT milk

the main nutritional components of milk are milk fat, protein, sugar, minerals, vitamins, etc. Among them, fat, protein (amino acids) and vitamins are easy to be oxidized by oxygen and lose nutritional value and fresh taste

there are two effective ways to prevent oxidative deterioration. One is to reduce the circulation and storage temperature (usually ℃), so as to reduce the oxidation rate. This is why milk is usually kept in the refrigerator. However, it is not easy to maintain a low temperature of ℃ in the circulation process and storage conditions, which is limited by equipment conditions and high economic costs

another way to prevent oxidation is to use barrier packaging materials to block the passage of oxygen into the packaging to prevent milk from being oxidized

barrier packaging materials for UHT milk

at present, the milk packaging used in the market mainly includes plastic bags and cartons. Among them, plastic bags are traditional packaging forms, which have the advantages of simple packaging and convenient circulation. Plastic bags can be divided into full plastic bags and aluminum foil bags. The latter has good room temperature packaging performance, but it is not easy to recycle due to the mixing of metal and plastic. From the perspective of environmental protection, all plastic bags have more advantages

as mentioned in the previous section, all plastic bags must have sufficient oxygen barrier function. Figure 1 shows the oxygen barrier properties of several commonly used food packaging plastic materials. It can be seen that when the relative humidity is not higher than 80%, the ethylene vinyl alcohol copolymer products (evaltm, Ebal TM) of Keli company have the best barrier performance. In high humidity environment, its barrier performance is lower than PVDC

but in fact, it is usually used in the form of multilayer composite film, and eval is sandwiched in the middle of the PE layer, so the surrounding humidity is not very high. For example, Eval is used for 50 thick each μ Between PE layers of M, when the relative humidity inside and outside the bag is 50% and 100%, the relative humidity of Eval layer is about 75%. In this case, its barrier property is still higher than that of other materials such as PVDC. In addition, due to the high processing difficulty of PVDC, the chlorine produced during combustion is not conducive to environmental protection, so it is basically replaced by other materials in advanced countries

the structure of multi-layer milk bags

we analyzed the structure of 14 kinds of all plastic milk bags on the market at present. Its multi-layer structure mainly includes the following:

A: PE (white)/pe (black); B: PE (white)/pe (colorless)/pe (black); C: The total thickness of PE (white)/tie/eval/tie/pe (black) is μ m. Eval layer thickness is about 5 μ m. Accounting for 5% of the total thickness

next, we will make a simple comparison of the oxygen penetration of the above bag membranes. Suppose the film thickness of milk bag is 100 μ m. The relative humidity of Eval layer is 65%, the ambient temperature is 20 ℃, the partial pressure of oxygen in the bag is 0, and the outside of the bag is air (the partial pressure of oxygen is 0.79 atmospheric pressure). It is assumed that the oxygen penetrating the milk bag makes the milk oxidized and absorbed, and the speed of oxygen penetrating the milk bag is constant within a certain period of time

at this time, the oxygen permeability of LDPE film is 5300cm3/m2.20 μ y. Similarly, the oxygen permeability of Eval h and E specifications is 2.2cm3/m2 respectively five μ Y and 4.7 cm3/m2.5 μ y。 The cumulative amount of oxygen penetrating into the milk bag membrane can be calculated, as shown in Figure 2

visible, also 100 μ M PE film, only 5 μ M Eval, after 90 days, the amount of oxygen infiltrated can be reduced by more than 1000 times from 477000 cm3/m2! Up to 198 cm3/m2 or 423 cm3/m2. So as to effectively prevent the oxidation and deterioration of milk! On the contrary, compared with Eval compound milk bag, for the current city, 7. Force measurement method: load sensor force measurement; The above two or three-layer film milk bags on the field inevitably cause people to worry that such a large amount of oxygen will enter, how can it not affect the quality and flavor of milk

in addition, because PE cannot block all microorganisms, it must inhibit the further growth and reproduction of invasive microorganisms. Eval's excellent oxygen barrier function can effectively inhibit the growth and reproduction of harmful aerobic microorganisms and facultative anaerobic microorganisms in milk

multi layer milk bag film processing method

eval multi-layer composite milk bag film can be prepared by 5 or 7 layers of coextrusion film blowing or casting equipment. The consumption of Eval is usually about 5% in the market. The use of Eval will not cause great pressure on material costs

according to the user's barrier performance requirements, equipment type and technical proficiency, Eval F, h, e and other specifications of Keli company can be selected respectively. Between LDPE or LLDPE and eval, adhesive resin needs to be used, which is sold in the domestic market. Eval multilayer composite film used with UHT milk bags is also sold on the domestic market

conclusion

to sum up, in order to ensure the safe circulation of UHT milk at room temperature and maximize the protection of nutritional value and flavor, Eval multilayer composite film is one of the best packaging materials at present. Compared with the two-layer or three-layer milk bags currently circulating in the market, the material cost of only 5% of the consumption will increase, which will greatly reduce the risk of commodity reputation and economic compensation losses caused by deterioration in normal temperature circulation. Perhaps it is for this reason that UHT milk manufacturers using Eval multilayer composite film in China have increased rapidly this year, and the supply of milk film once exceeded the demand. It is expected that it will be recognized and adopted by more and more manufacturers in the future, so as to promote the more stable and substantial development of UHT dairy industry

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