Among the natural foods available to humans, most foods are composed of their unique intrinsic substances and water. Water is a decisive factor in the growth and enzymatic action of various microorganisms, and fresh foods quickly deteriorate due to the presence of moisture. In order to prolong the storage time of food, people used immersed natural conditions such as sunlight and wind to remove water from its interior more than 3,000 years ago. With the advancement of human society and the development of science and technology, people have created a variety of dehydration technologies, such as hot air drying, cold air drying, spray drying, vacuum freeze drying, etc. These dehydration technologies have their own different characteristics. Vacuum freeze-drying technology is the most valuable value for food preservation and quality assurance, because only freeze-drying technology can maintain its color, taste, shape and nutrients for the longest and longest time. Food vacuum freeze-drying is hailed as the main symbol of technological progress in the food industry in the 20th century.
1. Advantages of food vacuum freeze-drying technology
Vacuum freeze-drying is a process in which the hydrated material is frozen, kept in a frozen state, heated in a vacuum environment, and the ice is sublimed into steam and discharged, thereby removing moisture from the material to obtain a lyophilized product. Since the process is carried out under low temperature and low pressure, and the moisture does not directly sublimate through the liquid, the freeze-dried product can maintain its natural color and odor substantially unchanged, the appearance shape is basically unchanged, and various nutrients such as protein and vitamin are basically unchanged and inherent. Substantially no loss of material, vacuum freeze-drying technology has unparalleled advantages of other drying techniques. (1) Drying is carried out under high vacuum, oxygen is scarce, oxidizable substances are protected, and sterilized by oxygen deficiency or inhibits the viability of certain bacteria. (2) Drying is carried out under low pressure, and the dried material is not oxidized and deteriorated. (3) Drying is carried out at a low temperature, and the heat-sensitive component which is easy to exert in the material is not denatured or loses vitality. (4) The material that is dried when frozen can form a “skeletonâ€, which remains in its original shape after drying, does not shrink, and has a loose porous sponge structure inside. (5) Dehydration is thorough. When drying, it can remove about 90% to 95% of water. After drying, it can be stored at room temperature for a long time, and it is easy to transport because of its light weight. (6) The rehydration product is excellent, and the freeze-dried product can be quickly recovered by water absorption, and its color and quality are basically the same as those of fresh products.
2. Application status of food freeze-drying technology
2.1 Foreign application status
Food vacuum freeze drying technology originated in the 1930s. In 1930, Flosdorf in Denmark began a freeze-drying experiment. In 1940, Fikidd in the United Kingdom proposed a technique for food processing by freeze-drying. In 1961, the British Food Department began research on food freeze-drying technology at the Aberdeen experimental plant. The research results show that freeze-drying technology is a method for obtaining high-quality food for food processing. According to relevant information, there were 11 freeze-dried food factories in the United States in 1963, and 25 European countries such as the Netherlands, Denmark, and former West Germany. In 1965, the number of global freeze-dried food plants has grown to more than 50. By 1972, there were 41 freeze-dried food factories in the United States, 13 in Japan, and 49 in Europe. The production of freeze-dried foods has also increased rapidly, only from the United States. In 1963, the output of freeze-dried foods was nearly 5,000 tons, 1970.
The output was 157,000 tons, and the output in 1972 was 175,000 tons. In the early 1980s, a large-scale freeze-dried food production line was built in Slutsk, Belarus, with an annual output of only 150 tons of freeze-dried cheese. In 1985, there were 25 freeze-dried food factories in Japan and nearly 100 in Europe. In 1989, Sofia, Bulgaria established the Institute of Cryobiology and Lyophilization in Sofia to study aerospace foods, children's foods, convenience foods, health foods and nutritious foods. At that time, the comprehensive strength of the institute ranked among the best in the world. From the mid-1980s to the end of the 1990s, it was the rapid development stage of global freeze-drying technology, and the yield of freeze-dried food in the United States and Japan increased the most. By 2005, there were more than 100 freeze-dried food factories in the United States and 35 freeze-dried food factories in Japan. Nearly half of the convenience foods in the United States and Japan were produced by freeze-drying technology. Freeze-dried food has been widely accepted in Europe, the United States, Japan and other countries.
The world's first food vacuum freeze-drying equipment was introduced in Denmark in 1943. After more than half a century of development, industrial developed countries now have the ability to independently develop food freeze dryers. The food freeze-drying machine is divided into different types according to the use. There are experimental freeze dryers and production freeze dryers; according to the size of the dry shelf area, there are four types: small, medium, large and extra large (the freeze-dry area is below 50m2). It is small, 50-100m2 is medium-sized, and 100-500m2 is large.
500m2 or more is extra large); according to the freezing method, there are freeze-dry combination and freeze-dry separation; divided into batch, semi-continuous and continuous according to the operation mode; divided by dry shape, square and round And tunnel type; according to the degree of automation, there are manual, semi-automatic and fully automatic. Atlas of Denmark and Concord Vacuum Co., Ltd. are the most influential food freeze-drying equipment manufacturers in the world. Denmark is the country with the largest export volume of freeze-drying equipment, and the United States is the country with the largest number of freeze-drying equipment. Atlas Company produces a complete range of food freeze dryers, of which freeze-dry separation and continuous food freeze-drying equipment are reasonable in structure, high in automation and low in energy consumption, and the main technical indicators are in the leading position in the world. The former can be semi-continuously produced by bulk loading, lyophilization and transportation of the loading vehicle; the latter is suitable for the production of large-scale freeze-dried food. The food freeze-drying equipment developed by Gonghe Vacuum Co., Ltd. is generally intermittent. This type of machine works periodically, and the materials are dried in batches.
2.2 Domestic application status
The development of vacuum freeze-drying technology in China has only been more than 50 years old. Vacuum freeze-drying technology was introduced from the former Soviet Union in the mid-1950s, when it was mainly used for the production of biological products and pharmaceuticals. In the 1960s, the country established a freeze-dried food base in Beijing, Shanghai, and Tianjin for strategic needs, and produced special foods for military, marine, and other field operations. Since then, food vacuum freeze drying technology has begun to be applied in China. In the mid-1970s, Shanghai and Guangdong built a freeze-dried food production line, mainly producing food industry raw materials and seasoning foods. Due to the backward freeze-drying process, high production cost and lack of market competitiveness, no one has been able to maintain operations until 1985. In the past two decades, with the rapid development of China's economic construction and international freeze-drying technology, China's food freeze-drying technology has made great progress. Qingdao No. 2 Food Factory took the lead in introducing freeze-drying equipment from Japan Gonghe Vacuum Co., Ltd., then Hunan Kangbao Food Company introduced the freeze-drying equipment from Atlas Company of Denmark, and Xiamen Jiayu Food Company introduced Taiwan equipment to make the application of freeze-drying technology in China continue. expand. At present, more than 20 freeze-dried food production enterprises have been established in Shanghai, Guangdong, Shandong, Fujian and other places; the universities that carry out research on food freeze-drying technology include Tsinghua University, Hefei University of Technology, Shanghai Jiaotong University, Northeastern University, Northeast Agricultural University. More than ten, in the development of garlic powder, soup, mushrooms, ginseng, yam and some fruits, vegetables and other freeze-dried foods, have achieved certain results.
The development of food freeze-drying equipment in China began in the mid-1980s, and it started late and developed rapidly. The early freeze-drying equipment mainly used foreign products in the 1970s, and its freeze-drying area usually did not exceed 20m2. The operation modes were intermittent, high energy consumption and low automation. In the past ten years, through the joint efforts of universities, research institutes and manufacturers, China has explored a road of combining digestion and absorption with innovation, gradually forming the capacity of independent design and independent production, and in the localization of food freeze-drying devices. Significant progress has been made, filling gaps in large-scale development, and developing freeze-drying equipment close to the international advanced level in the 1990s. For example: TH-FD50 freeze-drying machine of Tsinghua University Nuclear Energy Technology Design and Research Institute, DG series freeze-drying machine of Lanzhou Institute of Physics, Chinese Academy of Sciences, LG series freeze-drying machine of Northeastern University Mechanical Engineering College, food preservation project development of Guangdong Refrigeration Society Center FD series large freeze dryer. By the beginning of the 21st century, more than 20 manufacturers including Shenyang Xinyang Space Freezing Equipment Company, Guangzhou Great Wall Refrigeration Equipment Company, Lanzhou Kejin Vacuum Freeze Technology Company and Nantong Refrigeration Equipment Company have the ability to manufacture food freeze-drying equipment.
2.3 Types of freeze-dried food
According to statistics in the United States, by 2005, there were more than 100 kinds of foods produced by freeze-drying technology in the world, which can be divided into the following categories. (1) Cooking ingredients: meat, eggs, fish, shrimp, shellfish, sea cucumbers, vegetables. (2) Seasoning foods: onions, ginger, garlic, spices, pigments, soups. (3) Fruits: apples, bananas, pineapples, strawberries, pears, peaches, etc. (4) Drinks: coffee, tea, juice, vegetable juice. (5) Health foods: ginseng, yam, honey, turtle, and Cordyceps sinensis. (6) Native products: mushrooms, day lily, camphor, etc. (7) Food industry raw materials: egg material, bean material, dried fruit powder, plant egg ***, etc. (8) Special foods: food for field operations such as aerospace, navigation, military, mountaineering, and expedition.
3. Development trend of food freeze-drying technology
After entering the 21st century, with the increasing awareness of environmental protection and health, the pace of life is accelerating, people have a higher understanding of scientifically processed foods and put forward more requirements, which will greatly promote food vacuum freezing. Further development of drying technology. In this regard, according to the current situation of foreign new food development, from the international market for the analysis of the trend of demand for freeze-dried foods.
3.1 Freeze-dried foods being or are being developed abroad
(1) New convenience foods. In Japan, new convenience foods are supplemented with vitamins, whole egg powder or egg yolk powder, soy flour or peanut powder produced by freeze-drying technology to ensure their nutritional content. In most countries in Europe, the convenient foods made by mixing the daily consumption of germ corn flour with coconut oil, sugar, vitamins and minerals are the first generation of convenience foods; the second generation of convenience foods is lyophilized kelp powder. , natural fruit powder, seaweed gum, maltodextrin plus appropriate amount of citric acid and corn germ, oat germ, fish meal, meat-free powder, beef powder and so on. There is also a nutritious, sweet and delicious fruit-type convenience food in Europe and the United States. It is made from a mixture of lyophilized strawberry powder, grape powder, orange orange powder, pineapple powder, banana powder and kiwi powder. The Czech Republic is studying the lyophilization process for thin-layer materials used to process new convenience foods. Italy is studying the physicochemical properties of freeze-dried apple, lemon and sugar homogenized mixture and dehydration after milk. Spain is studying lyophilization. Dried lactic acid, Japan is studying freeze-dried gelatinous fish meal. Dr. J. H. MacNeil of the University of Pennsylvania predicts that eggs of this century will be concentrated by freeze-drying techniques into eggs with a solids content of 18% to 25% or 30% to 40%.
(2) Granular vegetables. Vegetables are a great treasure trove of human life. Japan Toyo FD Food Co., Ltd. found an unusual method of eating in the 1990s. The method comprises mixing eight kinds of vegetables such as rape, spinach, celery, radish leaves, peas, carrots, pumpkins, and snow red, and lyophilizing them to form granule vegetables. This vegetable rich in natural nutrients such as chlorophyll, carotene, vitamins and minerals is not only nutritious and delicious, but also suitable for infants at the beginning of weaning, children who do not like vegetables, and elderly people with bad mouths. Special populations such as patients who eat liquid or semi-liquid food and athletes with limited food intake. Now, granular vegetables have become the daily consumer goods of the Japanese public.
(3) Powder vegetables. In the European, American and Japanese markets, a new vegetable processing method has become increasingly popular, that is, lyophilized technology is used to process many kinds of powdered vegetables such as onion, cabbage, spinach, carrot, and pumpkin. Adding powdered vegetables to flour or sugar to make vegetable noodles, biscuits, cakes and confections, beverages, etc., can maintain the nutrients, fiber quality, color and flavor of vegetables.
3.2 International market demand for freeze-dried foods
In recent years, the demand for freeze-dried food in Europe, the United States and Japan has increased rapidly. In Europe, freeze-dried foods account for 50% to 70% of all dehydrated foods; among the nation's convenience foods, freeze-dried foods account for more than 50%; in the dehydrated foods on the Japanese market, freeze-dried foods are close to 60%. Despite this, the UK, Germany, the United States, Japan and other countries need to import a large number of freeze-dried foods each year, the varieties are round onions, asparagus, cabbage, carrots, mushrooms, potatoes, as well as beef, eggs and fish and shrimp. Imports of freeze-dried vegetables and freeze-dried fruits in the Nordic countries such as Sweden, Norway and Denmark are still increasing year by year. The price of freeze-dried food on the international market is 4-6 times that of hot-air dried food, and it is gradually becoming a staple food of international trade. According to the statistics of the State General Administration of Customs, since the mid-1990s, the annual export volume of dehydrated vegetables in China has increased by an average of 30%; the export volume of dehydrated vegetables in mainland China exceeds 1/2 of the total global output, plus exports from Taiwan. The volume accounts for about two-thirds of the world's total production.
China is a large agricultural country, rich in vegetables (including native products), meat and aquatic resources, using freeze-drying technology (the price of domestic freeze-drying equipment is only 1/3 to 1/2 of imported equipment), and developing freeze-dried vegetables, Large-scale foods such as freeze-dried beef and freeze-dried fresh eggs are sold to the international market and are an export-oriented foreign exchange project with promising prospects, high profits and low risks. At present, the freeze-dried food produced in China is basically external demand type, mainly including cooking raw materials, food industry raw materials, seasoning foods and health foods, with an annual output of less than 20,000 tons. According to industry insiders, in the next decade, China's external demand and domestic demand freeze-dried foods will enter a period of substantial growth; by 2015, only one instant noodle supplement, about 50,000 to 60,000 tons of freeze-dried food, plus fast food ingredients, Soups, drinks, etc., the consumption of freeze-dried food will exceed 150,000 tons. The huge demand for freeze-dried foods at home and abroad provides a great opportunity for the development of China's food freeze-drying technology and freeze-dried food industry.
4 Conclusion
Food vacuum freeze-drying technology is an interdisciplinary comprehensive technology involving multiple disciplines and fields. Advances in food freeze-drying technology depend on the development of interdisciplinary subjects. From the development status of food freeze-drying technology, industrial developed countries have become mature and perfect, and the popularity of freeze-dried food has reached a fairly high level; China is in the stage of combining, digesting and absorbing and independent innovation, and today's international advanced level. Compared with a certain gap, freeze-dried food has not been widely accepted by people and is not competitive in the domestic market.
As the saying goes: People eat for food. The food industry is closely related to the national economy and the people's livelihood. Only the more development and progress, the more scientific and scientific. Functional foods, nutritious foods, health foods, convenience foods, and children's foods are all indispensable for the development of new foods that meet the growing needs of people's material needs. Therefore, food vacuum freeze-drying technology will become an important application technology in the 21st century.