Table of Contents
Sterile packaging refers to a packaging technique that sterilizes the packaged food and packaging material containers separately, and completes filling and sealing under sterile environmental conditions.
The aseptic packaging technology was invented in the 1940s. Since the 1960s, thanks to the rapid development of packaging plastics, the market share of aseptic packaging has rapidly increased. Currently, aseptic packaging has been widely used in the packaging of liquid foods such as milk and dairy products, juice, and tomato sauce.
Food that has undergone aseptic packaging has minimal loss of color, aroma, taste, and nutrients (such as 95% retention of vitamins), and product quality remains consistent regardless of packaging size.
Sterile packaged food can be stored for 12-18 months at room temperature, and its flavor can be maintained for 6-8 months without the need for refrigerated storage, refrigerated truck transportation, or refrigerated cabinet sales. It is particularly suitable for packaging heat-sensitive foods.
The most significant feature of aseptic packaging technology is that the packaged food and packaging container materials are sterilized separately, which are independent of each other and effectively solve the shortcomings of traditional canned sterilization methods.
The loss of color, aroma, taste, and nutritional value of food is small, with low energy consumption. It can also achieve continuous sterilization, canning, and sealing, with high production efficiency. Regardless of the packaging size, the quality can be guaranteed, such as the preservation rate of vitamin C reaching 95%.
Sterile packaging is particularly suitable for liquid or semi liquid flowing foods, characterized by good fluidity and the ability to undergo ultra-high temperature instantaneous sterilization (UHT) or high-temperature short-term sterilization (HTST). The above sterilization methods are of great significance for maintaining flavor quality in heat sensitive foods such as milk, fruit and vegetable juices, etc.
The aseptic packaging process of food includes: sterilization treatment of packaging machinery and operating environment, sterilization of packaged food, prefabrication and sterilization treatment of packaging containers, quantitative filling, sealing, boxing, packaging, transportation, etc. All process steps must ensure the sterile conditions of food packaging operation.
If any stage of processing, packaging, filling, and sealing is not thoroughly sterilized, it will have an irreparable impact on the quality of the product.
Sterile food packaging materials, [email protected]
Basic concepts and principles of sterile packaging
Food aseptic packaging is basically composed of the following three parts: first, pre sterilization of food materials; The second is the sterilization of packaging containers; The third is the aseptic filling and sealing environment. These are the three main elements of sterile food packaging.
As the key to aseptic packaging technology is to ensure sterility, its basic principle is to kill microorganisms in a certain way and prevent microbial contamination. There are three main mechanisms of microbial death.
Mechanical failure mechanism
It assumes that microorganisms have a so-called “control center” that determines their survival. Destroying this control center can cause microbial death. This can be explained by the target theory of mortality and the logarithmic lethal law.
Chemical action mechanism
Emphasize the changes in the amount of important substances produced by anti metabolic effects. It requires quantitative chemical analysis data to illustrate.
Principle of Vitality
Using local interference in metabolic processes as the basis for bactericidal mechanisms. It requires qualitative biochemical analysis data to illustrate.
To establish aseptic packaging technology, it is necessary to comprehensively and flexibly apply existing sterilization and sterilization technologies to ensure that food, containers, and operating environments meet the prescribed sterilization levels.
Aseptic packaging conditions and sterilization methods
Aseptic packaging requires that while sterilizing the contents of the food, the microorganisms adhering to the surface of the containers or packaging materials used for packaging the food must also be thoroughly killed. The aseptic packaging process should meet the following requirements.
- Modern high-speed packaging machines must complete the sterilization of the surface of packaging materials (containers) in a short period of time.
- There is good wettability between the fungicide and packaging materials or containers.
- Fungicides should be easily removed from the packaging material or container surface.
- The sterilization method used is harmless to the operator and also harmless to consumers
- Residual fungicides should not affect product quality or consumer health.
- The sterilization method should ensure that the packaging materials used are non corrosive.
- Has environmental adaptability.
- The operating method is reliable and economical.
The sterilization of packaging materials and containers can be divided into three categories based on their mechanisms: physical methods, chemical methods, chemical methods, and the combination of physical methods.
a) Heating sterilization method
Different sterilization methods are suitable for different packaging materials and containers. Thermal methods are generally not suitable for sterilization of paper and plastic containers, while metal cans and glass containers can be fully sterilized by heating, such as using saturated steam, superheated steam, or hot air treatment.
Although superheated steam has excellent sterilization effects, due to its high pressure, it is only suitable for sterilization of pressure vessels, such as metal cans.
The use of microwave for sterilization is actually a thermal lethal sterilization method. This method can quickly heat up packaging materials with moderate moisture content.
Especially on the inner surface of packaging materials, heat can be quickly generated without rapid conduction and diffusion, resulting in the most easily contaminated and thoroughly sterilized parts of the packaging being sterilized and disinfected.
Due to the characteristics of short heating time, easy adjustment of thermal energy intensity, high heating efficiency, flexible operation, and convenient control, microwave radiation is an effective new technology in the food packaging industry.
Plastic packaging materials may have pinholes after being heated by microwave, and the strength of the material is weakened due to temperature and tensile force. Aluminum foil material is not suitable for microwave sterilization due to its reflective function against electromagnetic radiation.
b) UV sterilization
For containers made of paper, plastic film, and their composite materials, heating method is not suitable for sterilization.
For the sterilization of the surface of such materials, it is necessary to first consider cold sterilization, that is, using chemical or radiation methods to obtain composite plates through co extrusion technology. The maintenance of the sterile surface is achieved by a thin film (peel layer) called a protective layer covered on the surface.
By using radiation sterilization, packaging materials and containers can be sterilized through efficient ultraviolet radiation.
c) Ionic radiation method for sterilization
The use of ion radiation to treat packaging materials can also control the growth of microorganisms.
Many research results have shown that radiation sterilization is feasible for most food packaging materials, and when the radiation dose is 10kGy or lower, the mechanical and chemical properties of the packaging materials change very little.
When the radiation dose is high, the inherent properties of the packaging material undergo significant changes, especially when plastic undergoes polymer cross-linking reactions or main chain breakage, unsaturated bond activation, hydrogen gas or other gases release, or oxidation reactions occur, forming peroxides (when radiation is carried out in the air).
Halogen-containing plastics are highly sensitive to radiation dose and emit hydrogen halide gas.
After being irradiated, cellulose molecules will break, undergo decomposition, and lose its tensile strength.
- Hydrogen peroxide water sterilization
Hydrogen peroxide is a highly bactericidal agent with low toxicity and no corrosive effect on metals. It can decompose into “new ecological” oxygen at high temperatures.
This decomposed “new ecology” of oxygen is extremely active and has strong bactericidal ability, while water can immediately vaporize at high temperatures, resulting in minimal residue of hydrogen peroxide on packaging materials.
At present, sterile packaging machines that use hydrogen peroxide alone for sterilization use hydrogen peroxide with a concentration of 30% to 35%. By heating the surface of packaging materials with sterile hot air to around 120 ℃, hydrogen peroxide can be decomposed into water and oxygen, achieving good sterilization effects.
The US Food and Drug Administration allows sterile packaging to use hydrogen peroxide as a disinfectant for food packaging materials, with a maximum residue limit of 0.01mg/kg.
- Ethylene oxide sterilization
Ethylene oxide is a gas at room temperature, with a boiling point of 10.4 ℃. It has a wide range of bactericidal effects on cells. Its characteristic is that it can be sterilized at low temperatures and can also sterilize non barrier packaging materials.
The disadvantages are long sterilization time, flammability, certain toxicity, and long escape time. Therefore, in aseptic packaged food, ethylene oxide is generally mixed with gases such as carbon dioxide and used as a fungicide for prefabricated paper boxes or plastic cups.
- Sterilization with sodium hypochlorite
Chlorine ions are commonly used for disinfection of drinking water, and commonly used chlorine disinfectants include chlorine gas, sodium hypochlorite, chlorine dioxide, calcium hypochlorite, calcium chloride, etc.
Chlorine ions generally have a strong bactericidal effect on vegetative cells, but a weaker bactericidal effect on bacterial buds.
The biggest drawback of using chlorine fungicides is that residual chlorine is difficult to eliminate and has an impact on the flavor of food.
Method of combining chemistry and physics
- Combination of hydrogen peroxide and ultraviolet radiation for sterilization
The combination of hydrogen peroxide and ultraviolet radiation will produce astonishing bactericidal effects. Low concentration hydrogen peroxide solution (<1%) combined with high-strength ultraviolet radiation will immediately produce strong bactericidal effects at room temperature, which is 100 times stronger than using both alone.
Even when combined with hydrogen peroxide solution with a concentration as low as 0.1%, ultraviolet radiation has a significant bactericidal effect.
At this concentration, only 0.1mL of hydrogen peroxide is used as packaging material for a 1L capacity paper box. This is an economical and efficient sterilization method, and no measures are required to meet the maximum residue limit requirement of hydrogen peroxide.
- UV combined with citric acid or ethanol for sterilization
70% ethanol or citric acid alone has no bactericidal effect, but when combined with ultraviolet light, it can meet the bactericidal requirements within 3-5 seconds.
FFS plastic film bags are not injection molded, they are blow molded. Continuously producing “Form Fill Seal” (FFS) blow molded film products for bags is a heavy packaging film technology developed in China in recent years, mainly used in automatic packaging lines for large synthetic resin products such as polyethylene and polypropylene. The tube film method (i.e. blowing film process) has become the best production method for FFS bag film products in China.
Japan Printing Corporation has combined UV-C ultraviolet lamps with citric acid for the sterilization of packaging materials in FFS’s thermosetting plastic box aseptic packaging machine.
The bottom film and cover film of the plastic box are pulled from the film roll to the citric acid solution tank for soaking, then irradiated with ultraviolet light for sterilization. The bottom film is then thermally formed into a plastic box, filled with sterile materials and sealed with a film heat seal.
Sterile food packaging materials, [email protected]