Attention has been paid to the pharmacological actions of natural elements since hazardous properties of artificial synthetic things contained in foods and medicines have come to be indicated. Lots of catechins, polyphenols, are contained in green tea. It is known that the catechins have many actions such as antioxidation and antibacteria. Effective use of catechins in green tea is expected. For extracting the green tea catechins, the hot water extraction method and the organic solvents method are used. Although the hot water extraction is safe, the heat causes changes in quality and loss of catechins. Extraction at low temperatures is desirable to avoid these changes, while efficiency of the extraction is low. Authors have made studies to raise the efficiency by using ultrasound and have found that ultrasonic irradiation is effective. In this study, the effect of ultrasonic frequency on the promotion of extraction was mainly examined. Ultrasonic frequencies used were 25, 45, 100 and 130 kHz. Catechins extracted versus irradiation time were measured. It was found that the extraction was promoted by ultrasonic irradiation in all frequencies. The degree of promotion increased with frequency in the examined frequencies.
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