Reaction Kinetics of Degradation and Epimerization of Epigallocatechin Gallate (EGCG) in Aqueous System over a Wide Temperature Range

Abstract

(-)-Epigallocatechin gallate (EGCG) is the most abundant catechin in green tea, which has been linked with many health benefits. To ensure the conceivable health benefits from thermally processed products, a kinetic study on the stability of (-)-EGCG in aqueous system was carried out using a HPLC-UV system and Matlab programming. Simultaneous degradation and epimerization of (-)-EGCG were characterized during isothermal reactions at low temperatures (25-100 degrees C) combined with previously conducted experimental results at high temperature (100-165 degrees C); the degradation and epimerization complied with first-order reaction and their rate constants followed Arrhenius equation. Mathematical models for the stability of (-)-EGCG were established and validated by the reactions at 70 degrees C and with varied concentrations from different catechin sources. Two specific temperature points in the reaction kinetics were identified, at 44 and 98 degrees C, respectively. Below 44 degrees C, the degradation was more profound. Above 44 degrees C, the epimerization from (-)-gallocatechin gallate (GCG) to (-)-EGCG was faster than degradation. When temperature increased to 98 degrees C and above, the epimerization from (-)-GCG to (-)-EGCG became prominent. Our results also indicated that the turning point of 82 degrees C reported in the literature for the reaction kinetics of catechins would need to be re-examined.

Effects of different brewing conditions on catechin content and sensory acceptance in Turkish green tea infusions

“…These observations are in correspondence with other results published in literature that indicate high extraction temperatures improve extraction efficiencies because the heat renders the cell walls more permeable to solvents and components and increases the solubility and diffusion coefficients of the tea components to be extracted (Vuong et al 2011). However, excessive extraction temperatures above 80°C can cause degradation of the catechins by promoting the change in epistructured catechins to non-epistructured catechins (Wang et al 2008). They indicated that the content of non-epistructured catechins (i.e.…”

“…Epimerization can occur at high temperatures. Wang et al (2008) reported that the concentration of catechins decreased while their isomers increased at increasing temperatures. Degradation of catechins was evident as there was a declining trend in total catechins with increasing temperature.…”

Purification and Characterization of a Novel Galloyltransferase Involved in Catechin Galloylation in the Tea Plant (Camellia sinensis)

“…In addition, the galloylated catechins EGCG and ECG (Fig. 3), but not (ϩ)-gallocatechin-3-gallate (GCG), were detected by the two-step enzyme assay via TLC and HPLC (data not shown), which indicated that the cis-catechins EGC and EC were appropriate substrates of a galloyltransferase instead of the trans-catechin GC or C. These data further confirmed that EGCG and ECG in the tea plant are biosynthesized via enzymatic galloylation of EGC and EC with ␤G, whereas GCG in green tea beverages is derived from isomerization of EGCG during green tea production (33).…”

Determinação de enantiômeros em extratos vegetais por cromatografia quiral e dicroísmo circular

“…Os menores valores encontrados para a epicatequina na infusão podem estar relacionados a possíveis processos de degradação (OSZMIANSKI et al, 1996;JIANG, 2008). Isso também foi observado em nossos ensaios (Seção 4.5).…”

“…Embora a epimerização das catequinas seja mais lenta em soluções ácidas, a temperaturas acima de 40 o C podem provocar degradação ou polimerização das mesmas JIANG, 2008). Além disso, metais podem catalizar a degradação de catequinas em meio aquoso (OSZMIANSKI et al, 1996).…”