Epimerisation and hydrolysis of catechins under ultrasonic treatment.

Summary: This study investigated the influence of ultrasonic treatments on the chemical conversions of catechins. Ultrasound treatments significantly enhanced the epimerisation and the hydrolysis of catechins in both the catechins solution and the tea extract solution. Catechins are more stable in the tea extract solution compared to the catechins solution. The conversion of catechins induced by ultrasound can be controlled by temperature and pH. Regard to the pyrogallol‐type catechins, both the epimerisation and the hydrolysis were enhanced at the higher temperatures (60 and 70 °C) and the acidic condition (pH 6). The epimerisation and the hydrolysis of (‐)‐epigallocatechin gallate (EGCG) improved by 47% and 18%, respectively, when the temperature rose from 50 to 70 °C. Compared to pH 8, the epimerisation and the hydrolysis of EGCG at pH 6 improved by 27% and 39%, respectively. This study can be utilised to develop appropriate ultrasound‐assisted method to produce particular catechin monomers. [ABSTRACT FROM AUTHOR]