Freeze-dried foods refer to dehydrated foods that have been freeze-dried. It is a new type of food that specializes in fresh foods to ensure freshness and shelf life. From the aspect of quality, it is superior to traditional hot air drying, spray drying, vacuum drying and other dehydrated foods; from the perspective of storage and transportation, it is far superior to quick-frozen foods and canned foods.
Freeze-dried food packaging characteristics 1. Freeze-dried food quality characteristics The most important characteristic of freeze-dried foods is through freeze-drying, including freeze-sublimation drying and vacuum freeze-drying, to maximize the moisture content of foods to discharge moisture. Its quality characteristics are as follows.
(1) The shrinkage rate of freeze-dried foods is much lower than that of other dried foods, which can maintain the form of fresh foods.
(2) Freeze-dried foods have no surface hardening phenomenon, but when rehydration, moisture can quickly penetrate into the interior of freeze-dried foods, thus having excellent rehydration performance.
(3) Freeze-dried foods avoid the destruction of heat-sensitive components and the oxidation of easily oxidized components in common food processing. Therefore, the freeze-dried foods have the highest retention of nutrients and physiologically active ingredients.
(4) Freeze-dried foods are processed at a low temperature. They do not suffer from discoloration caused by pigment decomposition, browning caused by enzymes and amino acids, and can be used as a raw material without adding pigments when reconstituted. .
(5) Freeze-dried foods have a low volatility during processing, and the concentration of aromatic components after drying is relatively increased and the aroma is more concentrated.
The above quality characteristics determine the packaging characteristics of the freeze-dried food.
2. Characteristics of freeze-dried food packaging (1) Freeze-dried foods are completely dehydrated without adding any preservatives, and they can be safely stored for a long time with proper packaging.
(2) Freeze-dried food structure is porous sponge-like. If it is improperly packaged, it will easily absorb moisture and deliquescence once it is exposed to air.
(3) The specific surface area of ​​freeze-dried foods is relatively large, and oxygen in the air is easily brought into contact with the interior of the food. Over time, the fatty acid will be rancid by oxidation, which needs to be controlled by packaging technology.
(4) The relative density of freeze-dried foods is relatively small and the volume occupied is relatively large. In addition, the porous vegetable structure is fragile and inconvenient for transportation (transportation after packaging treatment is required).
The quality characteristics and packaging characteristics mentioned above are exactly what we must consider when designing and choosing packaging methods and technologies.
Frozen food packaging techniques The main purpose of freeze-dried food packaging is to solve problems such as moisture absorption, moisture absorption and oxidative deterioration.
1. Moisture-proof packaging techniques Freeze-dried foods easily absorb moisture and become moist, which means that they can easily absorb moisture from the air inside the package during packaging or storage. Studies have shown that freeze-dried foods generally have the highest water absorption rate within 80 hours, and hygroscopicity is also related to the processing freeze rate and different items.
The hygroscopicity of freeze-dried foods is related to factors such as temperature, air pressure, and different food ingredients. In order to reduce the moisture absorption speed, high-barrier sealed packaging materials can be used. By vacuuming the packaging and filling the packaging with special gas (such as nitrogen), the moisture absorption speed can be reduced and the shelf life of fresh products can be extended.
2. Oxidation-proof packaging technology method Oxidation of freeze-dried foods during storage of the package mainly refers to the oxidation of fat in their components and oxidation of carotenoids in oil-soluble components, oxidation of chlorophyll, oxidation of ascorbic acid, and the like. Due to the presence of oxidation, it is difficult to avoid changes in product color and loss of vitamins.
The degree of oxidation of fat is rather serious when the moisture content is low, because the water molecules adsorbed on the oil are partially broken during drying, and it is easy for the surface of the fat to be oxidized by contact with the oxygen in the air. Therefore, it is difficult to resist oxidation only by the packaging technique that reduces moisture.
To sum up, the measures considered in the anti-oxidation packaging are to use packaging materials with oxygen absorption function, add antioxidants, and make the inner layer of the packaging have the function of water balance (the inner layer of the packaging is coated with a water-retaining agent) so as to maintain a certain moisture in the packaging. , Low temperature storage, and good light blocking materials can be used.
3. Packaging materials selection Freeze-dried food packaging materials should use materials with special functions. These materials should have the functions of sealing oxygen barrier, strong light blocking and buffering.
Preferred freeze-dried food packaging materials are: aluminum foil composite materials, such as aluminum foil and polyethylene composite; glass paper, polyethylene, aluminum foil, polyethylene four-layer composite; paper, polyethylene, aluminum foil, paper, polyethylene five-layer composite; aluminum foil, Polyethylene, polyvinylidene chloride three-layer composite and so on. There are also metal cans and glass bottles used for freeze-dried food packaging. The outer package or large package is mostly packaged in corrugated boxes for the purpose of cushioning and shatterproofing.
4. Other packaging measures (1) Put the temperature-absorbing agent and oxygen-absorbing agent in the sealed package. Hygroscopic agents are: lime, activated carbon, silica gel (natural or synthetic products). Oxygen absorbers are also known as deoxidizers. Deoxidizers are mainly iron-based deoxidizers and sodium-based deoxidizers.
(2) vacuum packaging method.
(3) Modified atmosphere packaging method. After the bag (container) is drawn out of the air, it is filled with nitrogen and other gases and sealed.
Summary 1. Freeze-dried foods are a new type of processed foods that are promising and marketable. Their packaging requirements are mainly moisture-proof and oxidation-proof.
2. The packaging technology of freeze-dried foods mainly adopts vacuum packaging technology and modified atmosphere packaging technology, or add moisture-proof agent (suck absorber) and deoxidizer in vacuum packaging, which is an ideal packaging technology.
3. It is particularly important to choose packaging materials, and use more composite packaging materials with better barrier properties.
4. In fact, microorganisms must also be considered in production and packaging, but they are not analyzed in the text. Because in the freeze-drying process, there is often a certain amount of microbes remaining, but it is only when the water is scarce that the spores are not revived. Once the water is increased, it will be revived. Therefore, measures should be taken during processing, packaging, storage and transportation to sterilize and ensure compliance with the standard sanitary conditions. (Yang Fuxin)
Freeze-dried foods have become a new type of processed food that has become popular all over the world. Before the food is freeze-dried, it can be processed or eaten by simply restoring the original color, smell, and taste of the food after it is sprayed. Freeze-dried foods can be easily reconstituted, and the color, aroma, and taste of fresh foods are retained as much as possible, and at the same time, the original nutrients and physiologically active ingredients of foods are also retained. Therefore, freeze-dried foods have now become high-quality instant foods, making many functional foods or high-grade food materials mostly freeze-dried food materials, and also make freeze-dried foods become high value-added food or raw materials. In some developed countries abroad, freeze-dried food has become an important staple food for athletes, field force soldiers, astronauts and other special professionals. It also occupies an important position in civilian foods. For example, 50% of Japan's fast and convenient foods are freeze-dried foods. In the international market, freeze-dried foods cost more than four times more than traditional dehydrated foods. China's freeze-dried food has just started, but it is predicted that the future freeze-dried food will become a rising star in China's food.