Application of Microwave in Tea Bleaching and Drying

- May 07, 2019 -

China is a big tea producer, and tea-making industry is a traditional industry in China. After years of groping and research, the application of microwave in the field of tea green-killing and drying has made significant breakthroughs. In the application of microwave in tea green-killing, microwave heating was used to passivate the activity of polyphenol oxidase, evaporate part of water, volatilize the odor of green grass and soften the tissue. At present, the method of stir-frying is commonly used in production, and steam is used in a few places. The results showed that the quality of tea processed by microwave and stir-fried methods was good, and there was no significant difference, but the time of microwave could be continuously shortened. Because of the high moisture content of steam and the influence of high temperature on the outer layer of raw materials, the weight of tea leaves has hardly been reduced, some chlorophyll has been destroyed, and the nutrients in raw materials are partly lost with the condensation water, so the quality of raw materials is not ideal. The application of microwave in tea green-killing is mainly due to its thermal effect. When the magnetron produces microwave, the polar molecules in the tea are affected by the periodic change of microwave, and they move periodically with the microwave. Because of the high frequency of microwave, a large amount of friction heat generated by the collision of tea molecules can rapidly increase the temperature of the material, so as to achieve the effect of rapid heating. Application of

Microwave Tea Drying In the process of general hot air drying, the material is heated outside, the surface is dried, and the heat is transferred inward. The direction of heat transfer is opposite to that of water diffusion, which affects the outward evaporation of water. Microwave heating is internal heating, and the part with high moisture content warms up faster. Therefore, in the process of microwave drying, moisture migration from inner layer to outer layer is faster, and drying speed is obviously faster than hot air drying. The application of microwave drying in tea drying has the following advantages: fast drying speed; good product quality; because the surface temperature of tea is not too high, the chlorophyll changes little, the color is green and green, the storage is durable, the fragrance loss is less, and the drying is even; at the same time, because of the rapid evaporation of water, it is easy to form porous, the product has good rehydration, and the content is easy to dissolve when making tea. On the basis of traditional technology, tea quality can be improved by one or two grades by microwave sterilization. At present, the tea drying equipment successfully developed by our company includes honeysuckle drying equipment and chrysanthemum drying equipment.

Microwave tea insecticidal and mildew-proof application in tea storage and transportation is prone to insects, and insect contamination often occurs in the process of black tea stacking. In the past, the insecticidal methods of medicinal incense were commonly used, but there was a problem of drug residue. Good insecticidal effect can be achieved by microwave treatment. The insecticidal effect of insects in tea is closely related to the dielectric properties of tea and insects. When the moisture content of tea is less than 12%, it is beneficial to enhance the insecticidal effect. Tea is very susceptible to dampness and mildew during processing and storage, thus reducing its quality. Microwave technology has excellent bactericidal effect on tea mould. The application of microwave extraction equipment in the extraction of tea leaves can not be separated from the extraction process in the processing of tea soft drinks. At present, the conventional method of tea extraction is hot water extraction. Microwave extraction of active ingredients in tea has the characteristics of fast extraction speed, short extraction time and high extraction yield. The general extraction steps are: putting a certain amount of tea in the microwave extractor, adding appropriate amount of water, then controlling the equipment at the required temperature and time, starting to heat the extraction, and finally filtering the tea. Microwave sterilization has a good effect in

P>sterilization. Microwave sterilization is the result of the combined action of microwave thermal effect and biological effect. The thermal effect of microwave on organisms is to denaturate proteins and cause microwave biological death, while the biological effect of microwave on microorganisms makes the microwave electric field change the diameter distribution of cell membrane cross section, affect the concentration of electrons and ions around cell membrane, thus change the permeability of cell membrane, and inhibit the growth and development of microorganisms and death. In addition, strong microwave electric field can lead to hydrogen bond relaxation, breakage and recombination in DNA and RNA of organisms, thus inducing genetic mutation. Because microwave sterilization utilizes the destructive effects of thermal and non-thermal effects on organisms, its sterilization temperature is lower than that of conventional methods, which is conducive to maintaining the aroma of tea drinks.

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