Catechin stability in commercial teas during their shelf-life

Tea, second only to water, is the most widely consumed beverage in the world and is obtained from the leaves of Camellia sinensis L. (family Theaceae). Tea leaves, in particular those of the non-fermented green tea, are very rich in catechins (representing up to 30% of dry weight) and other polyphenols, which show significant antioxidant activities in vitro. More recently, some in vivo scientific studies have been performed in scientific papers, where some convincing evidences supporting healthy properties of green tea are described. These benefits include: improving blood pressure, serum cholesterol reduction, prevention of low density lipoprotein oxidation and, as a consequence, decreased risk for cardiovascular disease and cancer (De Mejia et al., 2009). The healthy effects are mainly associated with catechins, whose activity strongly depends from the amount intaken and bioavailability. Numerous studies have been published on catechin bioavailability, but results are widely variable. Several factors could affect the amount of catechins reaching the target tissues/organs after consumption; among others: medium pH, temperature, oxygen availability, the presence of metal ions, concentration of other active ingredients and storage condition. The aim of this study was to investigate the main catechin (epicatechin, epigallocatechin gallate and epicatechin gallate) relative abundance and total polyphenol content in different tea samples commercially available in Italy (green and black, including tea-based beverages). The second objective was the assessment of catechin stability during the shelf-life. The stability of catechins is important to guarantee the potential healthy effects of tea for the whole period of commercialization. Catechins during tea shelf-life were analysed by RP-HPLC (Phase A: water: formic acid 99.5:0.5 v/v); phase B acetonitrile: formic acid 99.5: 0.5 v/v). Profile of total polyphenol content and antioxidant activity were also assayed by using Folin-Ciocalteu’s colorimetric method and DPPH (2,2-diphenyl-1-picryl-hydrazyl) assay, respectively, using gallic acid as a standard (Chan et al., 2007). In green tea, the average content of total catechins decreased significantly by 2.44% to 40.72% in the first nine months. The correlation between catechin content and tea expiration period will be considered and discussed.