Scientific Reports volume 13, Article number: 10507 (2023 ) Cite this article
In present work, the degradation behavior of tea catechins on various commercial glazes was elucidated for the first time. Four kinds of Japanese typical commercial glaze powders (Oribe /Namako/Irabo /Toumei) based on Fe/Co /Cu /Ti oxides were utilized and deposited on ceramic tiles. Tea solution extracted from green tea leaves at 80 °C and then utilized for the examination of degradation behavior with glazes to meet a nearly identical condition in human daily tea drinking with ceramicwares. It was found that the degradation of tea catechins significantly dependent on the chemical structure of glazes, that is: Fe/Cu/Co oxides contained glazes can promote the degradation of epigallocatechin, epicatechin, epigallocatechin gallate and epicatechin gallate, while Ti oxide contained glaze stimulated the degradation of epigallocatechin gallate selectively. Coloring pigments were produced in degraded tea solutions, whose color shows glaze dependent property. We presume that these color pigments can be assigned as oxytheotannin, especially theaflavin and its oxides as well as thearubigins, that produced through the polymerization of intermediate free radical catechin and/or the ortho-quinone generated by catalytic effect of glaze oxides worked as Lewis’s acids. The specific function of glazes on degradation of catechins discovered here not only provides principal information for design and development of functional materials but also bring new impacts on daily tea drinking and long-term human health-related issues.
Tea, with a long history date back to around 2700 B.C. has become one of the most popular drinks in human’s daily life due to the existence of natural flavonoids such as catechins which have been reported as protective agents against cardiovascular disease and cancer1,2,3,4,5. The degradation of different tea catechins has been studied with respects to the effects of pH and temperature in lab level. Konatsu et. al. reported that reaction of epicatechin (EC) was accelerated when pH is higher than 6.0 while inhibited under pH lower than 5.0 with isomerization reaction occurred in acidic media6. The reaction of tea catechins including epicatechin (EC), epicatechin gallate (ECg), epigallocatechin (EGC) and epigallocatechin gallate (EGCg) fitted an apparent first order reaction kinetics at temperature below 95 °C. Chen’s group studied the degradation of variable green tea catechins under higher temperatures up to 98 ℃and 120 °C and they suggested that epimerization of EGCg to gallocatechin gallate (GCg) was observed7. In addition, Liang’s group reported the degradation of catechins in alkaline solutions under various lights and it was demonstrated that free radical species can be generated followed with polymerization via a photoreaction8.