Analytical Identification and Quantification of Catechin for Quality Control of Green Tea Samples Marketed in Brazil

To support the chemical quality control of green tea, this study aimed to develop and validate an integrated analytical workflow for the extraction, identification, and quantification of catechins applicable to routine industrial analysis. Green tea samples in sachet and bulk forms were extracted with water and partitioned with ethyl acetate. The phenolic and flavonoid profiles of the ethyl acetate fraction were characterized by mass spectrometry (MS) and nuclear magnetic resonance (NMR), confirming the presence of catechins and supporting sample authentication. Antioxidant activity was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays, while cytotoxicity was assessed in 3T3 fibroblasts by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Quantification of (+)-catechin was performed using a validated high-performance liquid chromatography (HPLC) method, showing strong linearity (R = 0.995), precision with relative standard deviation (RSD) values of 2.60% (repeatability) and 2.45% (intermediate precision), and high sensitivity with limits of detection and quantification of 0.0637 and 0.2123 mg L–1, respectively. The retention time of (+)-catechin under optimized conditions was 5.98 min, with a total run time of 15 min. For an extract concentration of 2 mg mL–1, the ethyl acetate fraction contained 0.420 mg mL–1 of catechin, corresponding to approximately 21% of the extract. The sachet tea extract exhibited higher flavonoid content and stronger antioxidant activity than the bulk tea, demonstrating the ability of the method to discriminate products based on chemical quality. Unlike most reported approaches based on aqueous or hydroalcoholic extracts, this study demonstrates that ethyl acetate fractionation significantly enhances catechin enrichment, enabling faster analysis and improved sensitivity using conventional HPLC-UV/DAD instrumentation. Compared to more complex analytical techniques, the proposed approach offers a rapid, cost-effective, and reliable alternative for routine quality control, although it is limited to targeted catechin quantification. This analytical strategy provides a robust tool for green tea authentication, batch standardization, and verification of antioxidant claims in food industry products.