How to guarantee the shelf life of soft liquid milk

With the development of the liquid milk business in the domestic market, people have higher and higher requirements for the packaging quality of liquid milk. According to analysis by industry insiders, people are increasingly demanding higher quality milk packaging because: First, consumer demand for high-quality milk products; Second, consumer demand for convenience, long-acting milk (UHT) is welcomed by consumers. Third, the need for the expansion of the dairy business market. High-quality packaging is an inevitable choice for companies to achieve local market penetration and expansion of foreign markets.

Plastic bag packaging occupies 70% of the entire liquid milk market with its economical advantages, and its shelf life issue has become the focus of consumers and milk producers.

The important factors affecting the shelf life of liquid fresh milk are as follows:

1. The oxygen permeability of the packaging material is good or bad. The pros and cons of oxygen barrier properties of packaging materials are the direct cause of the shelf life of milk. When packaged articles are exposed to the air, the oxygen molecules of the air penetrate through the molecular gap of the packaging material and penetrate the inside of the package in direct contact with the milk. When the oxygen that passes through reaches a certain amount, the milk will degenerate. With the development of the times, the milk packaging is packaged from the initial single-layer polyethylene plastic film bags to multilayer composite films. These multilayer composite materials incorporate aluminum foil or special coatings during the production process, which greatly improves the barrier properties of packaging materials to oxygen. The barrier properties (specifically referred to here as air permeability) are affected by the production process, coating thickness, and material composition. Impact. At present, the national standard on the testing method of material permeability is GB 1038. The test principle is the international common pressure difference method principle. Permeability test: The volume of gas that per unit area per unit time passes through a sample at a constant temperature and unit pressure differential. The standard temperature and pressure value in terms of volume, unit: cm3/m2 · d · Pa; gas permeability coefficient test: at a constant temperature and unit pressure difference, in the stable through time, through the sample per unit time Unit thickness, volume of gas per unit area. It is expressed as a volume value at standard temperature and pressure. The unit is: cm3·cm/cm2·s·Pa. Take the BTY-B1 breathability tester produced by the Jinan Languang Electromechanical Technology Development Center as an example. The experimental procedure is: place the sample on a high-speed quantitative filter paper (diameter 85mm), seal it in a permeable chamber, open the air source, and start the test. After the end, the system pops up a test report. Note: The physical properties of the tested diaphragm can be destroyed, such as flat, no scratches, no perforation, no other attachments on the surface, no elastic or inelastic stretching; ensure the laboratory temperature stability, "test temperature" Is one of the parameters in the calculation formula, its stability affects the reflection of data accuracy; before the test, the membrane should be strictly dried to avoid adhesion of moisture on the membrane to participate in the test; the coating film and the composite film should be tested separately.

2, the package sealing process is good or bad. Liquid milk soft packaging is mostly three-sided packaging, such as seal sealing quality problems, it will directly cause the invasion of oxygen, thereby accelerating the deterioration of milk. Package sealing is affected by two factors: First, the manufacturer's packaging process, one is the material itself heat sealing performance. The detailed specification of the test method for sealing performance is GB/T 15171. The principle is: In a certain degree of vacuum, the sample is placed in a vacuum chamber to observe whether or not gas escapes within a set period of time. The test method is: put the sample into the vacuum chamber, cover the vacuum chamber sealing cap, close the inlet valve. Open the vacuum valve to vacuum the vacuum chamber, adjust the vacuum to 30-60s to one of the following values: 20, 30, 50, 90 kPa, etc. When a certain degree of vacuum is reached, vacuum is stopped and the vacuum is maintained for one of the following times: 3, 5, 8, and 10 min. The adjusted vacuum value and vacuum holding time are determined according to the characteristics of the sample (such as the packaging materials used, the sealing conditions, etc.) or related product standards. However, the sample must not be ruptured or cracked at the seal due to excessive pressure difference between the inside and outside of the sample. Take the MFY-01A sealer manufactured by Jinan Languang Electromechanical Technology Development Center as an example. The experimental procedure is: place the sample into the vacuum chamber and inject proper amount of water into the vacuum chamber, set the test vacuum degree and test holding time, start the test and observe Whether there is bubble escape. If there is an escape from the air bubble, the test is terminated and the product's sealing performance does not meet the test requirements. Otherwise, the product is sealed.

There are three important indicators of material sealing performance: heat sealing temperature, heat sealing time, heat sealing pressure. The test method is: the sample is made under certain parameters, and a width of 15 0. lmm, and a length of 100±1mm is cut on the package in accordance with the requirements of the ZBY 28004 specification. The state-adjusted test specimens shall be expanded 180° with the heat-sealing part as the centerline. The two ends of the specimen shall be clamped on the two fixtures of the tester. The longitudinal axis of the specimen shall be connected with the center of the upper and lower fixtures. Coincide with each other, and be flexible enough to prevent the sample from slipping and breaking in the fixture. The distance between the clamps is 50mm, the test speed is 300±20mm/min, and the maximum load at which the sample is broken is read. If the sample is broken in the fixture, the sample is used as a waste, and the sample is taken to make up. The test environment temperature and relative humidity are the same as the state adjustment environment. Take the HST-H heat seal tester and XLW(L) produced by Jinan Languang Electromechanical Technology Development Center as an example. The test procedure is: set the test parameters such as preset temperature, time and pressure for the heat seal tester. After the parameters are stable, the test will be performed. Place the sample in both heads and press the test button. After the end of the test, the sample shall be taken as required by ZBY 28004 after the sample is cooled to room temperature. The two ends of the specimen are clamped on the XLW and the lower chuck respectively, and the specimen is adjusted so that its longitudinal axis coincides with the center line of the upper and lower jigs, and the elasticity is suitable. Select test speed, test, dynamic curve liquid crystal display test, print test report. Matters needing attention: to ensure the width of the sample, ensure that the longitudinal axis of the sample coincides with the center line, and ensure the tightness of the sample when clamping the sample.

The above are several important factors and test methods that affect the shelf life of liquid fresh milk. It is hoped that the majority of liquid milk producers and packaging material suppliers can find quality control and solutions for packaging materials.