Review Interaction of tea polyphenols with serum albumins: A fluorescence spectroscopic analysis Adity Bose n Department of Chemistry, Presidency University, 86/1 College Street, Kolkata 700073, India article info Article history: Received 2 May 2015 Received in revised form 30 August 2015 Accepted 8 September 2015 Available online 25 September 2015 Keywords: Tea polyphenols Serum proteins Fluorescence Binding constant Static quenching abstract Interactions of some tea polyphenols, namely ( ) Catechin (C), ( )-epicatechin (EC), (–) epicatechin-3- gallate (ECG), ( )-epigallocatechin (EGC) and ( )-epigallocatechin-3-gallate (EGCG) are outlined with the serum albumin proteins. These interactions had all resulted in binding with the proteins with a concomitant static quenching of the protein fluorescence. A fluorescence technique has been considered as the tool to comprehend the polyphenol–protein interactions mainly and simultaneously other spec- troscopic techniques used to verify the results have been discussed. In this mini review the different types of equations usually employed to calculate the binding constant values have been outlined, namely, modified Stern Volmer plot, Scatchard plot and Lineweaver Burk equation, with their corresponding results. The n values (number of binding sites) had always been close to unity suggesting a 1:1 com- plexation with the polyphenols and the protein. A structural change in the polyphenols has been found to alter the binding constant value and the galloyl moiety attached to the C ring of the polyphenols have been found to play a crucial role in this regard. It has been found that an increase in galloyl moiety increases binding of the catechins with proteins. & 2015 Published by Elsevier B.V. Contents 1. Introduction ........................................................................................................ 220 2. Methods ........................................................................................................... 221 2.1. Fluorescence quenching ........................................................................................ 221 2.2. Binding constants ............................................................................................. 222 2.3. Circular dichroism (CD) ......................................................................................... 222 2.4. Isothermal titration calorimetry .................................................................................. 222 2.5. FT-IR ........................................................................................................ 222 3. Results and discussions ............................................................................................... 222 4. Conclusion ......................................................................................................... 225 Acknowledgments ....................................................................................................... 226 References ............................................................................................................. 226 1. Introduction The history of tea began over 5000 years ago in ancient China. Currently, tea is a very popular beverage consumed by two-thirds of the world's population. Green tea, black tea, and Oolong tea are all derived from the leaves of Camellia sinensis plant and contain an assortment of compounds, the most significant components of which are catechins or polyphenols. Tea polyphenols, known as catechins, account for 30–42% of the dry weight of the solids in brewed green tea [1]. Catechins contain a benzopyran skeleton with a phenyl group substituted at the 2-position and a hydroxyl (or ester) function at the 3-position. Variations to the catechin structure include the stereochemistry of the 2,3-substituents and the number of hydroxyl groups in the B and D rings. Belonging to the flavan-3-ol class of flavonoids, major catechins found in tea Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence http://dx.doi.org/10.1016/j.jlumin.2015.09.018 0022-2313/& 2015 Published by Elsevier B.V. Abbreviations: C, Catechin; EC, Epicatechin; EGC, Epigallocatechin; ECG, Epicatechin-3-gallate; EGCG, Epigallocatechin-3-gallate; BSA, Bovine serum albu- min; HSA, Human serum albumin; αHSA, Human salivary alpha amylase; CD, Cir- cular dichroism; ITC, Isothermal titration calorimetry n Tel./fax: þ91 33 2241 3893. E-mail addresses: adityc17j@gmail.com, adity.chem@presiuniv.ac.in Journal of Luminescence 169 (2016) 220–226