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First, the application of microwave in tea greening production of green tea, oolong tea, all need to heat the treatment to passivate the activity of polyphenol oxidase, evaporate part of the water, volatile grass odor, soften the tissue. At present, the production method is often used to carry out the greening method, and in a few places, the steaming method is adopted. The test results showed that the quality of the tea processed by microwave sterilization and fried green was good, and there was no significant difference, but the short time of microwave sterilization (1/8 of the time of fried green) could be continuously carried out. Because of the high moisture content of steam, the outer layer of raw materials is affected by high temperature. Therefore, the tea leaves after greening have almost no weight loss, some chlorophyll is damaged, and the nutrients contained in the raw materials are partially lost with the condensed water, and the quality is not ideal. The application of microwave in tea killing is mainly the thermal effect it produces. When the magnetron generates microwaves and shines on the tea leaves, the polar molecules inside the tea leaves are affected by the periodic changes of the microwaves, and periodically move with the microwaves. Due to the high frequency of the microwave, the high-speed collision of the molecules inside the tea leaves generates a large amount of frictional heat to rapidly increase the temperature of the material, thereby achieving a rapid heating effect.
Second, the application of microwave in tea drying In the general hot air drying process, the external heat of the material, the surface is dry, the heat is transferred inward, and its direction is opposite to the direction of water diffusion, which affects the outward evaporation of water. The microwave is internally heated, and the part with a high water content heats up quickly. Therefore, in the microwave drying process, the migration speed of moisture from the inner layer to the outer layer is fast, and the drying speed is significantly faster than hot air drying.
The application of microwave drying in tea drying has the following advantages: (1) fast drying speed; (2) good product quality; less chlorophyll change due to less high surface temperature of tea leaves, green color and resistance to hiding, less aroma loss, and even drying At the same time, due to the rapid evaporation of water, it is easy to form porosity, and the rehydration of the product is good, and the contents are easily dissolved when the tea is brewed.
Third, the application of microwave in tea insecticide and anti-mildew tea in the process of storage and transportation is prone to insects, insect pollution in the process of black tea piles often occur. In the past, insecticides were commonly used for fumigation of drugs, but there were problems with drug residues. Microwave treatment can achieve good insecticidal effect, and the insecticidal effect of insects in tea is closely related to the dielectric properties of tea and insects. When the water content of tea is less than 12%, it is beneficial to enhance the insecticidal effect. Tea leaves are highly susceptible to moisture and mildew during processing and storage, reducing quality. The experiment proves that microwave technology has excellent killing effect on tea mold.
Fourth, the application of microwave in tea juice extraction Tea soft drinks (plus tea drinks, tea granules) processing is inseparable from the extraction process. At present, the conventional method of tea extraction is hot water extraction, and microwave extraction technology has developed rapidly in foreign countries. By 1995, foreign companies have authorized the application of industrial scale microwave extraction technology to two Chinese companies. Microwave extraction of the active ingredients in tea leaves has the characteristics of fast extraction speed, short time (one-third shorter than conventional methods) and high extraction yield. The general extraction step is: placing a certain amount of tea leaves in a microwave extractor, adding an appropriate amount of water, then controlling the apparatus at the required temperature and time, starting the heating extraction, and filtering to obtain the tea juice.
V. Application of Microwave in Sterilization of Tea Beverage Microwave sterilization is the result of the combined effects of thermal and biological effects of microwaves. The thermal effect of microwave on microorganisms is to denature proteins and cause microbial death. The biological effects of microwaves on microorganisms change the electric field distribution of cell membrane sections, affecting the concentration of electrons and ions around the cell membrane, thus changing the permeability of cell membranes. The performance causes the growth and development of microorganisms to be inhibited and die. In addition, a sufficiently strong microwave electric field can cause hydrogen bond relaxation, fragmentation and recombination in the DNA, RNA of the living organism. Thereby inducing genetic mutations. Since microwave sterilization utilizes the thermal and non-thermal effects on the destruction of organisms, the sterilization temperature is lower than that of the conventional method, which is beneficial to the maintenance of the aroma of the tea beverage.
VI. Application prospects of microwave technology At present, China's microwave technology and equipment are relatively mature, and microwave equipment for continuous, high-power and different purposes has been basically finalized. However, microwave dried tea also has some shortcomings, such as large investment and high power consumption. In fact, microwave dry operation combined with hot air drying is better.
Introduction to the application of microwave dryer in tea processing technology
Tea processing is a traditional industry in China. In order to improve the processing quality and industrial modernization of tea, it is necessary to apply new science and technology in tea primary processing industry and deep processing industry, and advanced microwave technology has a good application prospect in tea. Microwave refers to the ultra-high electromagnetic wave between the radio and the light wave at 3OMHz-300000MHz. Currently, microwave devices used in the food industry have a center wavelength of 0.328 m (frequency 915 MHz) or 0.1225 m (frequency 2450 MHz).