Identification of native catechin fatty acid esters in green tea (Camellia sinensis)

Catechins are potent antioxidants and make up the primary class of polyphenols present in tea (Camellia sinensis). They are especially abundant in the less-fermented green teas that have been employed in various foods to enhance shelf life stability (Senanayake, N. J. Funct. Foods 2013, in press. Gramza, A.; Korczak, J. Trends Food Sci. 2005, 16, 351-358). The antioxidative activity of native (polar) catechins has proven to be useful in foods of relatively high polarity, while mixed results have been achieved in high-fat foods. However, the polarity of catechins can be attenuated by esterification with fatty acids, producing adducts that effectively partition into lipids and protect against rancidity even in high-fat foods (Cutler, S.; Fuller, E.; Rotberg, I.; Wray, C.; Troung, M.; Poss, M. International Patent WO 2013/036934 A1, March 14, 2013. Zhong, Y.; Shahidi, F. J. Agric. Food Chem. 2011, 59, 6526-6533). In this work, a search for the presence of naturally occurring lipid-conjugated catechins was undertaken in various green tea varieties. Rather than the traditional aqueous infusion, dried tea leaves were extracted with organic solvents followed by analysis for catechin adducts with both lower polarities and increased molecular weights as monitored by liquid chromatography and tandem mass spectrometry. Native catechin palmitates were identified and indirectly confirmed by synthesis and nuclear magnetic resonance as natural components of several Chinese green teas. Evidence of other fatty catechin esters was also observed.