| Extraction is the first process of tea drink processing. As a new processing technology, microwave technology has the advantages of fast, high efficiency and energy saving due to its radiation heating principle. This paper uses the oolong tea as material to study the feasibility of the application of microwave heating equipment in tea drink extraction, and the effect mechanism of the microwave extraction technology applied on precipitation precursor particles formation in tea drink. Three extraction methods were carried, belt type microwave pretreatment for enhancing water bath extraction method, belt type microwave direct extraction method and conventional water bath extraction method respectively. The conventional water bath extraction method was used as a control. Comparison their tea soup quality standards, such as water extract contents total amount, tea polyphones extraction rate and work efficiency to optimize the method of belt type microwave extraction of Oolong tea drink. Microwave extracted the tea soup and separated the tea precipitation precursor particles. The dynamic light scattering was carried to analyze the characteristics of colloidal particles. The concentration distributions of main chemical components of tea were detected by high performance liquid chromatography. We combined with the supernatant and precipitate two phases of oolong tea, and their progressive process in three-phase phase transition, to explore the mechanism of precursor particles importance and the formation of precipitation.(1) Extracted the oolong tea soup by the belt type microwave method, compared it with belt type microwave pretreatment and conventional water bath methods. Four single factors were used to research, rehydration ratio, microwave pretreatment power, microwave pretreatment time and water bath time respectively. Optimization by the response surface, the optimal experimental condition was rehydration ratio 1:5, microwave pretreatment power 3k W, microwave pretreatment time 3min. Extraction the tea soup in condition of boiling water bath 10 min and the ratio of tea to water 1:20, experimental results showed that the content of extraction was 11.74mg/m L, the tea polyphones was 4.12mg/m L. Compared to 30 min conventional boiling water bath method, the content of tea polyphones is almost the same, but the water extraction was higher obviously. Under this condition, the working efficiency of microwave pretreatment method was increased 56% to the conventional method. This was validated by repeated experiments double times.(2) Extracted the oolong tea soup by belt type microwave direct extraction method, optimization by single factor and response surface, the optimal condition was tea water ratio 1:15, microwave power 2k W, microwave time 10 min. Compared to conventional water bath method, the content of water extraction and tea polyphones was almost the same. Under this condition, the working efficiency of belt type microwave direct extraction method was 33% to the conventional method. The predicted value of the model was only 3% to the actual value, so the model was effective.(3) Compare crawler microwave direct extraction and pretreatment combined with two extraction methods of water bath, pretreatment method of short(3 min), high power(3kw), tea water extract content in water bath is significantly higher than control, production time is bath control increased by 56%; Low power(2 kw), direct formulation with length(10 min), extraction of effective components of the beverage effect compared with water bath, 30% of the time for the traditional water bath method. Comprehensive test parameters and the practical production operation, the caterpillar microwave equipment is more suitable for pretreatment combined with water bath extraction way to achieve efficient continuous production of tea drinks.(4) Microwave extraction time, power than three conditions of oolong tea, tea, precipitate the formation of the precursor particles(large particles) similar to the trend of the water bath extraction, oolong, physical and chemical composition according to the size of the molecular mass of dissolution, successively in large particle distribution proportion with the increase of extraction time, microwave power, water bath temperature increase, gradually increase with the decrease of the tea than, colloidal particle number increases, more concentrated distribution. Leaching time is divided into the slow rise(20~140s)(180~180s microwave), a rapid and saturated balance period(300~360s microwave) three stages, microwave extraction colloidal particle number for 300 s dissolution enhance the critical point of balance and stability, Water bath extraction 45℃, 65℃, 85℃, respectively is oolong tea precipitation formation and the formation of stable particles begin to form, a large number of critical temperature point; Microwave power during 80~80w, combined with each other, such as protein and catechins colloidal particle number increase sharply and stability; Low power(240w) than high power(720w) for the majority of catechins in precipitation distribution of precursor particles have a role in promoting, 720 w high power extraction of colloid particle size decreasing, the rise in the Numbers, electrostatic repulsion, reduced stability of tea liquor; In high concentrations of tea than system, oolong, physical and chemical components concentration is highest, the protein concentration distribution rate of the largest(67.7%), but high concentrations of tea soup of big particle colloidal stability, easy reunion, and under the condition of the water bath extraction of three kinds of catechin distribution rate for microwave twice; Low concentration(1:100) system of tea than large particles of light intensity decreases, and loose particles distribution, stability is enhanced.(5) The supernatant on the microwave extraction oolong tea liquid precipitation, precipitation precursor particle, three-phase and colloidal properties of physical and chemical concentration distribution correlation analysis, physical and chemical components of microwave extraction oolong tea precipitation tend to be stronger than the water bath. In oolong tea to precipitate precursor particles to the precipitation in the process of transformation, the distribution of protein rate minimum value difference and precipitation rate(3.72%), precipitation tendency is the largest, the tendency of soluble sugar(41.49%); the weak Catechins(ester type, pyro type) and the key role of proteins, promoting effect on other free small molecules. Oolong tea colloidal particles in the supernatant, precipitate precursor particles to the precipitation of phase change process, growing Numbers(631.52 kcps growth), the particle size increase(244.73 nm), system stability enhancement(Zeta potential absolute value increase 10.28 m V); Colloidal particles physicochemical properties presented free liquid molecules into a stable characteristic of solid particles. |
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