The frozen food industry is one of the fastest growing industries in the world today. According to statistics from the commercial sector, the annual production and sales volume of fast-frozen foods in China is increasing at an annual rate of 25%, becoming an emerging food category closely related to people's lives. China's quick-frozen fruits and vegetables are mainly frozen vegetables, accounting for more than 80% of the total.
In the early 1980s, due to the needs of foreign trade, China's quick-frozen vegetables began to develop and developed rapidly, mainly in Shandong, Jiangsu, Zhejiang, Guangdong, Fujian and other southeast coastal areas, and the products were sold to 28 countries and regions. Japan is China's main fast-frozen vegetable exporter, accounting for 65.7% of total exports; the United States ranks second, accounting for 19%. The varieties with an export volume of over 2,000 tons are 7 kinds of taro, spinach, edamame, green beans, peas, asparagus and broad beans. However, China's quick-frozen vegetables account for a very small share of the international market, only about 1/30, and have great development potential.
With the reduction of production and sales costs, frozen vegetables are gradually favored by consumers in the domestic market. At present, domestic sales are mainly based on taro, sweet corn, cucumber, green pepper, kidney bean and eggplant. However, the corresponding quick-frozen equipment industry has benefited in recent years. The main products are spiral quick-freezer, fluidized quick-freezing machine and so on. In developed countries, the quick freezing method represented by single quick freezing is widely used in the processing of quick-frozen vegetables.
■How big is the gap between us and foreign countries?
Due to the strict requirements on the freshness of processed raw materials, the construction of raw material bases has the saying that “quick-frozen foods are fresher than fresh foods in the market”. Compared with other fruit and vegetable processing, quick-frozen vegetables require the establishment of high-quality green vegetables bases that are convenient for transportation and for processing. However, China's quick-frozen enterprises are still mainly based on acquisitions, and the level of mechanized harvesting and packaging in raw materials is still used. Very low. For the international market, the raw material planting structure needs to be adjusted. In addition to the clams, the fast-frozen vegetables produced in China have a small production volume of large varieties such as peas, sweet corn and potatoes, which have a large market share. There is a lack of research and intervention in the fast-frozen fruit market and the quick-frozen concentrated juice market, which have considerable trading volume on the international market.
Due to the large export demand for quick-frozen vegetables in recent years, some places have rushed to the blind production, and there have been many factories in one place, with investment of tens of millions of yuan. These new plants generally have prominent problems with good equipment but weak quality management, which leads to unstable product quality. In the overall consideration, there is a general lack of stable and excellent varieties of agricultural and sideline products production bases. Due to the above reasons, the production of quick-frozen raw foods is still the main export, the technical content and benefits are low, and it also provides conditions for foreign buyers to purchase.
Research on processing mechanism and technology China's fruit and vegetable quick-freezing industry is not enough in the research of processing mechanism and technology. Due to the increasing quality requirements for quick-frozen foods in foreign countries, the changes in fruit and vegetable foods during quick freezing and subsequent refrigeration have been paid more attention, and the research is also very deep. It is particularly noteworthy that foreign countries have conducted in-depth research on the influence of deep temperature and quick freezing on materials. The research on the “glassy” temperature of some typical materials has been transferred to the practical stage by establishing a database.
Production quality management Due to the complexity of food quick-frozen, the national standard gb8863-88 "quick frozen food technical regulations" currently only requires "as soon as possible" for the freezing rate, but it is generally believed that the quick freezing time and freezing speed of frozen food should be qualitative and Quantify two aspects to control. At present, some small and medium-sized enterprises in China do not have the equipment and technology needed for quick freezing, blindly launching, making quick freezing into slow freezing, and the quality of products can be imagined.
Developed countries are producing according to strict standards, and the quick-freezing process has also developed a trend toward the specialization of various fruit and vegetable foods. Thus, special quick-freezing workshops and special cold storages have emerged.
Development and development of quick-freezing equipment, cold source and low-temperature cold storage In the late 1980s, with the development and development of small-scale continuous quick-freezing machines by domestic scientific research and production departments, paving the way for the localization of quick-freezing equipment, the traditional quick-freezing room was compact. Replaced by various quick freezing equipment. However, the domestic quick-freezing equipment still uses the traditional compression chiller as the cold source. Although it has the advantages of safety, reliability and low cost, its refrigeration efficiency is very limited, and it is difficult to achieve deep cooling. In order to improve refrigeration efficiency and quick-freezing quality, foreign developed countries have adopted a large number of new refrigeration methods and new refrigeration devices. Refrigerators that are directly sprayed with liquid nitrogen, liquid Freon, and liquid carbon dioxide have been used in quick-freezer since the 1980s. These refrigeration units can lower the temperature to a much lower degree of cryogenic than ammonia compressors. It is precisely because of the emergence of these new refrigeration devices that it is possible to freeze the food at an ultra-low temperature, thereby greatly improving the quality of the food and causing reform of the freezing process.
In terms of the technology of freezing and storage of fruits and vegetables, there are eight major development trends in developed countries in recent years. Namely: cold storage single layering, prefabrication and assembly; cold storage tends to be low temperature and large; cold storage heat insulation tends to foam plasticization; cold storage handling mechanization; Freon for cold storage; piston and screw compressors are continuously optimized; air cooler Replace the cooling pipe; automatic control technology is applied to the cold storage.
At present, the domestic production capacity of continuous frozen vegetable production line of 2 to 5 tons/hour and low-temperature storage and transportation equipment for quick-frozen vegetables is still very low. The large-scale continuous quick-freezing machine for exporting quick-frozen vegetables is still mainly imported.
Thawing technology thawing method for quick-frozen vegetables
Quality has an important impact, and there are few studies in China. In developed countries, as some new technologies are gradually applied to the thawing of frozen foods, mechanism research and technology development such as microwave thawing, ohmic thawing, and far-infrared thawing are popular. .
In the face of the growing production and consumption of frozen food, the formation of cold chain in China appears to be lagging behind, and the storage capacity of cold storage is seriously insufficient, which causes seasonal fluctuations in the production and sales of products, which has a great impact on the quality of frozen vegetables. In developed countries, the ratio of quick-freezing capacity to refrigerated storage capacity is about 2:1, while in China it is about 8:1. From a macro perspective, the final formation of the cold chain requires the input of state funds, forming a one-stop operation of production, processing, circulation and consumption to ensure the supply of raw materials and the quality of frozen products, so that the frozen food industry can be connected with the international market as soon as possible.
■What technical problems urgently need to be solved
The construction of raw material bases should establish a research institute for quick-frozen fruit and vegetable varieties that combines science, industry, agriculture and trade, introduce internationally popular hot-fresh new varieties, and use bioengineering techniques to improve existing varieties, and develop and cultivate large varieties suitable for quick-freezing. In particular, it is necessary to cultivate a variety of "glassy" temperatures that are of interest to the frozen world as soon as possible, so that high-quality quick-frozen products can be realized on ordinary quick-freezing machines. In addition, a stable green vegetable raw material base should be established. Since vegetable quick freezing requires a very short time interval from harvesting to processing (within 24 hours), mechanized harvesting and packaging should be promoted at the raw material base.
Research on processing mechanism and technology The main changes in quick-frozen fruits and vegetables are vitamin loss, protein denaturation, color change and texture (such as tenderness, umami and water content). The observation, comparison and analysis of the superfibrous structure of the frozen fruit and vegetable varieties should be carried out by using advanced testing techniques such as electron microscopy to determine the variation of various materials in different temperatures, different freezing and refrigerating time, and determine the materials accordingly. The best process at each quick freezing stage.
Although -18 ° C is a recognized temperature standard for the frozen food industry, for some special vegetable varieties, lower temperatures favor the maintenance of its quality. The effects of various process parameters on the quality of these fruits and vegetables should be further studied in depth, and the experimental study on the "glassy" temperature of quick-frozen fruits and vegetables should be carried out to establish the "glassy" temperature of large varieties of fruits and vegetables in China. The database has made our country's high-grade frozen vegetables quality grade a step.
Strengthening the core technology in the production of quick-frozen concentrated juice--the research of ultra-precision filtration technology and reverse osmosis analysis technology makes China occupy a place in the production of quick-frozen concentrated juice.
Production quality management is jointly established by universities, commodity inspection and health inspection departments to regularly train the quality inspection personnel of export quick-frozen vegetable enterprises to help enterprises carry out intensive management and management, and gradually establish good operating procedures, so-called Gmp (goodmanuf-acturepractice), from primary processing to deep processing.
Development and development of quick-freezing equipment and cold source With the development of China's steel-making industry, the demand for oxygen has doubled, and the price of liquid nitrogen, which is a by-product of the oxygen-making industry, has rapidly declined, so the application of liquid nitrogen refrigeration equipment The outlook is optimistic. The current focus is to accelerate the development of high-speed (5 tons / hour or more) continuous spiral type quick-freezer, ultra-low temperature liquid nitrogen and carbon dioxide spray type quick-freezer and supporting fruit and vegetable pre-cooler.
Thawing technology and cold chain construction research on various new methods of rapid thawing, focusing on the microwave thawing, far-infrared thawing and ohmic thawing techniques widely used in foreign countries, and on this basis, the development of large-scale thawing machines of more than 2 tons / hour Meet the needs of the food ingredients industry. The storage capacity of refrigerated storage should be vigorously developed to increase its proportion in the cold chain. In 2005, efforts should be made to achieve a 4:1 ratio of quick-freezing capacity to refrigerated storage capacity.
