Discussion on food vacuum packaging technology

Generally, after the food is vacuum-dried in the market, the material is completely frozen, and the vacuum food ice crystals are sublimated under absolute vacuum to achieve the purpose of low temperature dehydration. Since vacuum dried products have the advantage that many other drying methods cannot be surpassed, the advantages in applying food processing are:

1. The vacuum-frozen food is convenient to eat. Because the food has been washed, cut, sealed and packaged during the packaging process, it can be eaten directly by using only one bubble when eating.

Second, from the aspect of food nutrition preservation, because it uses vacuum packaging to quickly freeze, and then sublimate and dry in a vacuum environment, the material structure of the food can be kept unchanged, such as the most vulnerable in fruits and vegetables. Vitamin C can maintain more than 90%;

Third, the fruits and vegetables after freezing and quick-drying are beautiful and beautiful, one does not dry, the other does not shrink, and the original shape and color of the food are maintained;

4. The food after freezing is light in weight, the eggs and various meats can be reduced by 50~60%, and the fruits and vegetables can be reduced by 70~90%;

5. Freeze-dried foods can be stored for a long time without deterioration. Generally, refrigerated and modified atmospheres can be stored for several months, up to a maximum of one year, while freeze-dried foods can be stored in closed iron cans for more than 5 years.

Since the food after vacuum freezing and quick drying consumes huge energy in the production process and the cost is high, since industrial production in the 1960s, more than half of the products are supplied to military needs, navigation, aerospace, polar exploration, geological prospecting, People who work in special occasions such as the frontiers bring great convenience to their work and life, and most of the rest are used as baby food or high-end convenience food. With the development of China's economy, in recent years, some high-end convenience foods have used freeze-dried shallots, parsley, shrimp, beef, etc. as seasonings or additives.

After rapid vacuum freezing of the food, the frozen material is placed in a vacuum packaging device, using an edible, water-incompatible, water-comparable heat-compressing material (now Only edible oils and fats, in the future it is possible to use alternatives to edible fats or oils or heat transfer media developed in accordance with the above requirements, which accumulate a large amount of heat at a certain temperature, through direct contact with frozen A method of dehydration in which the ice crystals absorb a large amount of heat energy in a very short period of time, directly vaporized or directly liquefied, and is essentially a sublimation in a special state, in order to be conventionally freeze-dried (hereinafter referred to as conventional freezing). The sublimation of dry) differs according to the characteristics of sublimation in this special state, so it is named as fast vacuum freeze drying (hereinafter referred to as rapid freeze drying).

Generally, in this special case of sublimation, there is no similar report on the literature that I can see. The author believes that there are reasons for this to be sublimated:

1. Comparing the time-pressure curve with the time-pressure curve of conventional freeze-drying, the shape and direction of the two are very similar, which is equivalent to changing the time unit of the conventional freeze-drying curve from hour to minute.

Second, the fast freeze-dried products are very close to the conventional freeze-dried products in terms of dehydration ratio, rehydration performance, rehydration rate, brittleness, appearance shape, color and so on.

Third, the conventional dehydration theory was used to analyze the dehydration process, which was consistent with the experimental results.

Certainly some people will think that this is actually a vacuum low-temperature frying technology. In fact, there is an essential difference between the two: vacuum low-temperature frying technology is to fry unfrozen materials in a vacuum container, at the beginning In an instant, sublimation occurs under the above special circumstances, but since the hot oil and the ice crystal are separated by a layer of hot steam that has just been sublimated, the heat transfer efficiency is greatly reduced, and the heat energy cannot be transmitted under the special circumstances. Sublimation, and turned into ice (solid) - → water (liquid) - → steam (gas) process, because the phase change of the two is different, the processed products are very different, fast freeze-dried The products are not achievable in the products of vacuum low-temperature frying technology in terms of brittleness, oil content, preservation rate of nutrient active substances, and rehydration performance.

Vacuum foods have advantages and disadvantages compared with fast freeze-dried foods. Conventional freeze-dried foods have higher nutrient activity preservation rate, oil-free products, and are suitable for long storage periods;

Rapid freeze-dried products are higher in the preservation rate of nutrient active substances than other drying methods, second only to conventional freeze-drying. Due to the residual of edible oils (heat transfer medium), the storage period is only about one year, but the oil content is not High, dry goods are about 5-8% (15-20% for vacuum deep-fried products), about 0.5-1% after rehydration, similar to daily diet. As a food processing, this feature is Acceptable, and fast-freeze-dried products have a high-temperature ripening and sterilization process during processing, and their rehydration performance, preservation rate of nutrient active substances, etc. are close to conventional freeze-dried products, and therefore, in many occasions It can replace conventional freeze-dried products and can also be eaten directly.

In terms of the range of processing types, rapid freeze-drying almost completely covers the scope of conventional freeze-drying. Since the production cost of rapid freeze-drying is only 20%-50% of the cost of conventional freeze-drying, many conventional freeze-drying methods have almost no market. After switching to rapid lyophilization, the products have become extremely competitive in the market. For example, instant noodles in food products, the products of quick freeze-dried products are superior to the currently available microwave drying instant noodles in appearance and internal quality; The convenient processing of rice noodles and instant rice, which is technically processed, truly becomes a convenient “rice”; in nut products, the products that are quickly freeze-dried are more crispy, fragrant and crispy than the products processed by traditional methods of frying, baking and roasting. And there will be no scorch; etc.; the fruit and vegetable products processed by the rapid freeze-drying technology are similar in texture to the puffed food, have the brittleness and oil content comparable to the biscuits, and do not add any chemicals during the processing. Is an excellent, high-quality health food suitable for people of all ages. The prospect of this type of product is very broad; in addition, fast Dried kelp, seaweed, livestock and poultry products, also has a broad market. To sum up, there are as many as 100 types of foods that can be quickly lyophilized: food, fruits and vegetables, livestock and poultry, seafood, and aquatic products. It can be said that there is no such food processing technology. A wide range of practical applications.

China is a big country with abundant agricultural and sideline products. There are many raw materials suitable for rapid freeze-drying technology processing all over the country. Many of them are also local special resources. Due to reasons of preservation, storage and transportation, some parts are greatly wasted every year. If the rapid freeze-drying vacuum technology is used to carry out in-situ deep processing, the economic and social benefits resulting from this will be incalculable.