| Black tea is loved by all kinds of food culture consumers all over the world because of its mellow flavor,pleasant taste,rich in various nutrients and functional edible value.Due to the limitations of the characteristics of tea,the consumption form of black tea is still mainly based on soaking.However,the fine tea culture does not satisfy the modern fast-paced lifestyle.Therefore,instant black tea can be produced and promoted,which retains the original eating habits of black tea and combines the advantages of convenient,quick and nutritious solid beverages.However,at present,the instant black tea products generally have such problems as low taste,sensory reduction,light aroma,loss of nutrients,and poor color.Food microcapsule technology is to wrap solid,liquid or gas food raw materials in microcapsules to improve food stability,mask taste,increase solubility and other functions.Therefore,in this study,the combination of the rapid dissolution of black tea and the microencapsulation technology is used by prepare the microencapsulated instant black tea.It could obtain a highly reductive tea soup by improving the quality and process loss of the instant black tea.The main research contents are as follows:1.The microwave-assisted selection of auxiliary aids and ultrasonic extraction process and conditions were explored in black tea.the extraction rates of polyphenols extracted by ultrasonic extraction and microwave extraction were 21.92% and 23.60%,respectively,and the contents of extracts were 28.15% and 28.71%,respectively.The comparison showed that the microwave-assisted leaching effect was better than the ultrasonic leaching with short time.Furthermore,the response surface optimization of microwave extraction conditions was carried out,and the optimal conditions for microwave-assisted extraction were determined: tea ratio 1:13.11,initial water temperature 62°C,microwave time 130 s,tea polyphenol extraction rate under this condition It was 23.52% and the leachate content was 28.95%.2.Four groups of wall materials were prepared by spray drying method.The optimum spray drying parameters were studied: the inlet air temperature was 180℃,Flow Injection was 52 mL,and the fan speed was 53 rpm.The physical properties of tea powder were analyzed.The results showed that microencapsulation could reduce the moisture content and hygroscopicity of tea powder,increase the fluidity and the gap between the powder particles,and improve the quality of instant black tea.XRD analysis showed that microencapsulation changed the crystal state of wall materials and tea powder.The combination of wall material and core material has a new phase,not a simple mechanical mixing.Comparing the particle size distribution,particle size and dispersibility index of the reconstituted solution and the extraction,the tea powder M4 reconstituted solution was closest to the original extract in terms of particle size distribution,particle size and dispersibility.Scanning electron microscopy was used to observe the microscopic morphology of microencapsulated tea powder.It was found that the four microcapsule tea powders were nearly spherical in shape surrounded by the outer membrane and unruptured,which proved the successful preparation of the tea powder microcapsules.The microencapsulation made the tea powder micro-structure non-adhesive and dispersible.Among them,tea powder M3 and M4 had better shape and quality.3.The embedding effect of microencapsulation was determined by aroma components,nutrients and color.The 63 volatile components were identified by SPME-GC-MS qualitatively.The results showed that the aroma types,relative contents and types of the four microencapsulated instant black teas were more than those of the non-microencapsulated tea powder,indicating that microencapsulation could reduce the loss of aroma in industrial processes.Among them,tea powder M3 had the most aroma components,which was more 16 types than non-microencapsulated tea powder.The protective effect of microencapsulation on the nutrient content of black tea was analyzed by the retention rate of tea polyphenols and caffeine in the original extract.The results showed that the microencapsulation of different wall materials increased the retention rate of the two nutrients,which verified the successful embedding of the components in the tea.Among them,the protective effect of tea powder M4 was the most significant,which showed by the polyphenols and caffeine retention rate of the non-microencapsulated tea powder of 21.31% and 19.50% higher;The the change of color was compared by the Hunter Lab colorimetric system.The results showed that the clarity of tea powder M2 was better,the color difference between tea powder M4 and the original extract was the smallest,and the degree of reduction was high.4.The thermal stability and moisture adsorption properties of the microencapsulated tea powder were separately explored to predict the stability during storage.The results of TGA and DSC showed that microencapsulation could delay the thermal decomposition temperature of tea powder and improve the thermal stability.The isothermal adsorption curve of tea powder showed that the water adsorption capacity of microencapsulated tea powder was lower than that of non-microencapsulated tea powder under the same temperature and humidity environment.It reduces the possibility of moisture,dissolution and deterioration due to water absorption during storage.The mathematical model was used to simulate the water adsorption law of tea powder. |
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