Effect Of Ultrasound-assisted Extraction On The Quality Of Green Tea Extract

Extraction is one of the important steps for further processing of tea leaves.The extracting effects have a relatively huge impact on subsequent production and processing.This paper treated green tea as raw material,and conducted comparative experiments between ultrasonic assisted water extraction and traditional hot water extraction.It also checked the content of aqueous extract,tea polyphenols,theanine,caffeine,catechin and so on from extracted liquid,determined liquor color of extracted liquid,evaluated extracted liquid by sense,observed the surface morphology of tea leaves by scanning electron microscope,and discussed the advantages of ultrasonic-assisted extraction and the influences to the quality of green tea extract.Details and main research results are as follows:This paper extracts green tea by water with ultrasonic wave as the auxiliary,designs the single factor experiment of the extraction yield of green tea water extractum and tea polyphenols influenced by ultrasonic time,ultrasonic power and ultrasonic temperature,designs the experiment of extraction parameters optimization using the response surface method on the basis of the result of the single factor experiment,and obtains the relatively good extraction parameters: 24.7 min ultrasonic time,496.18 W ultrasonic power and64.95℃ ultrasonic temperature.Under this condition,the extraction yield of tea polyphenols is 19.54%;in the verification testing,the extracting parameters are amended,i.e.,ultrasound time 24.7 min,ultrasound power 500 W,ultrasound temperature 65℃.Three repeated tests’ result is that the extracting rate of tea polyphenols is 19.47%,with a low deviation of 3.6% to the theoretical value.It shows that the optimum parameters gained from the experiment are reliable and have practical value.Comparative experiments among the ultrasonic-assisted water extraction at 65℃,the water extraction at 65℃ and the water extraction at 90℃ are designed,the results of which show that: With the extension of time,the water extract rate by the ultrasonic-assisted extraction method and the main chemical components of the tea are both higher than that by the water extraction method at 65℃ and 90℃,which illustrates that the ultrasonic assisted water extraction method can accelerate the leaching of effective components of tea.There is relatively great difference among the colors of extracting solution extracted from three extraction tests.The extracting solution extracted under the help of ultrasonic presents green yellow,the extracting solution extracted in the water of 90℃ presents red brown and the extracting solution extracted in the water of 65℃ presents yellow green;thebrightness of the extracting solution which is extracted from the water at 65 degrees centigrade is better;the brightness of the extracting solution which is extracted with the support of ultrasonic waves comes second,and the soup brightness of the extracting solution which is extracted from the water at 90 degrees centigrade is inferior;the extract from the 65℃ ultrasonic auxiliary water gets the highest score of sensory evaluation,and its taste and fragrance are strong;the extract from the 90℃ water gets the lowest score of sensory evaluation,and its bitter taste is strong with a stuffy smell;the extract from the65℃ water gets a medium score of sensory evaluation,and its taste and fragrance are of average level.It indicates that the ultrasonic-assisted extraction can help obtain the extracting solution of a better sensory quality from green tea.The leaf shapes of the tea residues got from the three experiments are observed by the scanning electron microscope.The result shows that the leaf surfaces of the tea residues are with such serious damage after the ultrasound-assisted extraction that the exposed cell tissues can also be seen;However,after extraction in 90°C water,the surface of the tea leaves presents destroy only on wax layer,not seriously damaged;and after extraction in65°C water,the surface of the tea leaves is intact without damage.The result illustrates that with the ultrasonic-assisted extraction,and thus the ultrasonic has a physical effect on the tea to extract more tea components,which endows the extract with dark color,strong taste and high aroma.