Longjing tea is one of China's famous historic teas. Its unique color, flavor and quality style are well known at home and abroad. Especially in recent years, Longjing Tea has been widely recognized by the market, and its production volume and sales volume have been increasing year by year. It has become the largest famous green tea in terms of production and sales volume. However, improper storage of Longjing tea during storage and transportation will directly affect its quality, leading to a significant decline in economic value and drinking value. Therefore, both producers and consumers attach great importance to the storage and preservation of Longjing tea. Longjing tea is finely produced, its processing technology is complex, and its economic value is high. However, the corresponding storage and packaging methods are relatively backward. Compared with the packaging of tea in Japan, China, Taiwan, and other domestic food packaging, Longjing tea packaging is relatively simple and has an effect of freshness preservation. difference. Judging from the storage and packaging methods of Longjing tea on the market, most small packages use iron cans, paper cans, or general plastic composite bags, which have poor barrier properties. At the same time, there are some problems in the large-scale storage of Longjing tea and storage in the household consumption process. Therefore, this article briefly introduces the quality change mechanism of Longjing tea during storage and its preservation methods in different occasions.
First, the mechanism of quality deterioration of Longjing tea and related preservation technology
The quality deterioration mechanism of Longjing tea is the same as ordinary green tea. Research at home and abroad shows that temperature, moisture, oxygen, and light are the four factors that affect the quality of stored green tea. The automatic oxidation of chemical constituents in tea leaves is the root cause of the deterioration of tea quality; moisture and temperature are the conditions for quality change, and they have the effect of accelerating or delaying the speed of oxidation reaction; light can change the quality of tea and promote the compound of pigments and lipids, etc. Oxidation has a certain decomposition effect on tea components. The most easily oxidized components of Longjing tea are: aroma components. Chlorophyll, vitamin C and polyphenolic compounds. Based on these findings, drying technology was used in tea storage. Low-temperature refrigeration technology. Vacuum deaeration and gas conditioning technology and other preservation techniques.
1. Drying technology
Drying technology is traditional tea storage technology, generally using lime. Charcoal, silica gel, etc. are stored together with tea leaves and have a certain effect. In theory, moisture has a great influence on the quality of tea. The dry tea moisture content should be as low as possible, and the general requirement is less than 6%. The relative humidity of the environment has a great influence on the moisture content of the dry strips. Generally, the relative humidity of the storage environment should be less than 60%. Drying technology is to extend the shelf life of tea. Preservation period and application of other preservation techniques.
2. Low-temperature refrigeration technology
The reaction rate of chemical constituents in tea leaves is closely related to temperature. Lowering the temperature can slow down most chemical changes, thereby suppressing various changes in the contents of green tea and maintaining its color, aroma, and other sensory qualities. A large number of research results at home and abroad have shown that in the existing tea preservation technology, the low-temperature refrigeration technology is the most advanced and has the best effect. Considering both the preservation effect and the cost saving, it is better to control the low-temperature refrigeration temperature of Longjing tea at 0-10°C.
3. Deoxygenation and pumping nitrogen filling technology
The relevant research results at home and abroad show that the vast majority of changes in the biochemical components of tea during storage require the participation of oxygen. Therefore, the process of tea aging can be inhibited under anaerobic and hypoxic conditions. Based on this research, oxygen scavenging agent degassing and nitrogen purging and nitrogen filling packaging technologies were used. It is generally believed that the effect of green tea using oxygen scavenger oxygen scavenging and nitrogen purging and packing technology is significant, which can reduce the degree of change in the sensory quality of green tea, enhance the storage performance of green tea, and prolong the effective storage period.
4. Other technologies
In recent years, some new preservation techniques have emerged. For example, the method of adding preservatives before or during the processing of green tea has a certain effect. Biological preservation technology is also a development direction of tea storage and preservation.
Second, Longjing tea post-natal packaging tea storage and preservation technology
1, using a dry, odorless warehouse storage
This method is simple, easy to use, low cost, have a certain effect, suitable for manufacturers with relatively poor economic conditions or storage of low-grade tea. Five times of drying are generally used, and dehumidifiers can also be used conditionally. The large amount of storage is generally stored at the bottom of the layer of lime, the upper layer of tea placed in large packages; storage can be used when the number of small packaging methods such as packaging, bags, etc., will soon be kraft paper packaged with Longjing tea into lime Store it in boxes or bags. The amount of lime should be determined based on the moisture content of the tea. The ratio of tea to quicklime is generally 4-5:1. This method should be observed in the use of the process, need to exchange lime regularly, at least 3-4 times a year.
2. Tea special cold storage
Considering the existing preservation technology, using low-temperature refrigeration is the most effective way to solve the large-scale storage of Longjing tea. Low-temperature refrigeration can make tea under low temperature conditions, and avoid light and dehumidify, which can greatly extend the shelf life of tea. The only disadvantage is that the equipment investment is large and the use cost is high. Formally, there are mainly combined cold storage and fixed-type civil cold storage for tea refrigerating. The combined cold storage capacity is relatively small (l-100m2), removable and assembleable, flexible installation, good heat preservation, safe and convenient, but the price is relatively high, and it is suitable for small-scale tea enterprises and retail departments to store high-end Longjing tea. The volume of civil cold storage is relatively large and can only be used in a fixed manner. However, the investment is relatively small, and there is a large selection of refrigeration equipment, which is suitable for large-scale storage of Longjing tea. The cooling capacity of the cold storage should be determined according to the size of the warehouse and the amount of tea stored. Generally, it should be equipped with automatic temperature control system to make the cooling system and cooling system work synchronously. It has the function of automatic temperature control and dehumidification. From the comprehensive consideration of the shelf life effect and economic benefits of cold storage operation, under the condition of relative humidity controlled to 65%, it is appropriate to control the tea storage temperature at 0-8°C.
Longjing tea in the cold storage process, due to a large difference in temperature inside and outside the library, storage and storage should have a transitional processing. Before entering the warehouse, the tea is placed in the pre-cooling room and then pre-cooled before being sent to the cold storage room. When leaving the storage room, the tea leaves the storage room for a few days after being stored in a relatively high temperature transition room.
Before the tea is stored, especially when the new cold storage is used for the first time, or when the relative humidity in the used storage tank exceeds 65%, ventilation and dehumidification should be performed in time. After a long-term use of cold storage, smells will appear inside the warehouse, which is detrimental to the quality of tea, and should be changed in time. Generally, it requires a thorough cleaning of the warehouse for 2-3 years to keep the warehouse clean and air fresh.
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