Improved quantification of catechin and epicatechin in red rice (Oryza sativa L.) using stable isotope dilution liquid chromatography-mass spectrometry

Epimerization can change the catechin content and composition of samples during extraction and analytical analyses. To control the effect of epimerization, we developed a novel and stable isotope dilution liquid chromatography-mass spectrometry (LC-MS) method using catechin-2,3,4-C-13(3) and epicatechin-2,3,4-C-13(3) as stable-isotope-labeled internal standards (SIL-ISs). When the SIL-ISs were used, the catechin and epicatechin contents were stable (104-109% and 100-109% of the initial concentration, respectively) despite long storage times. In contrast, when L-2-chlorophenylalanine was used as an internal standard, catechin and epicatechin concentrations of 88-97% and 164-277% of the initial concentration, respectively, were obtained after long storage times. Furthermore, the least significant epimerization effect and highest extractability were observed when extraction was performed at 70 ?for 30 min. The recoveries for red rice using the developed isotope dilution LC-MS method at two different concentrations were between 100.72 and 118.67%, with relative standard deviations less than 3.67%.

Automated summary

Epimerization can be controlled using stable-isotope-labeled internal standards to maintain stable catechin content. The least significant epimerization effect and highest extractability were observed when extraction was performed at 70℃ for 30 min.