Investigation of the interaction between soluble antioxidants in green tea and insoluble dietary fiber bound antioxidants Ecem Evrim Çelik, Vural Gökmen ⁎ Food Engineering Department, Hacettepe University, 06800 Beytepe, Ankara, Turkey abstract article info Article history: Received 11 January 2014 Received in revised form 18 February 2014 Accepted 22 February 2014 Available online xxxx Keywords: Green tea catechins Bound antioxidants Insoluble wheat bran Interaction of antioxidants This work investigates the possibility of interaction between insoluble dietary fiber bound antioxidants, specifi- cally of wheat bran, and soluble antioxidants like those provide by aqueous infusions of green tea. Solutions of pure catechins were also assayed for comparison with those naturally found in tea. To accomplish this, the aque- ous and alcohol soluble fractions as well as the lipid components of wheat bran were firstly removed and the freeze-dried insoluble residue was then treated with different concentrations of green tea infusions or aqueous solutions of epicatechin (EC) and epigallocatechin-3-gallate (EGCG) for certain time. Treatment with EC (0–200 μM) had no significant effect on the antioxidant capacity of insoluble bran fraction. However, treatment with EGCG significantly (p b 0.05) increased linearly the antioxidant capacity as a function of concentration (0–100 μM). Treatment with great tea infusions (1–3 g/100 ml) also increased the resulting antioxidant capacity of insoluble bran fraction, but the effect was lesser at higher infusion concentrations. Liquid chromatography cou- ple to mass spectrometry (LC–MS) analyses of aqueous phases after treatment indicated comparable levels of de- crease in the concentrations of catechins confirming their reaction with the radical forms of antioxidants bound to insoluble bran matrix. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Tea (Camellia sinensis L.) is the second most consumed beverage worldwide after water (Yang, Wang, Lu, & Picinich, 2009). Three differ- ent types of tea (green, oolong and black) differ in terms of their produc- tion techniques, leading to the presence of different compounds. Green tea (minimally processed) is characterized by its high content of flavan- 3-ols, namely catechins, whereas oolong tea (partially fermented) and black tea (completely fermented) by the presence of theaflavins and thearubigins (Rein et al., 2012). Several epidemiological studies have suggested an inverse relation- ship between heart disease, diabetes, neurodegenerative disease and even cancer with especially green tea consumption among other tea va- rieties (Grove & Lambert, 2010; Higdon & Frei, 2003; Siddiqui, Afaq, Adhami, Ahmad, & Mukhtar, 2004; Williamson, Dionisi, & Renouf, 2011). The proposed beneficial effects of green tea have been attributed to its catechin content (Anesini, Ferraro, & Filip, 2008). The major cate- chins found in green tea are (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin-3-gallate (ECG) and (-)-epigallocatechin-3- gallate (EGCG). Among them, EGCG is also the most abundant catechin present in green tea (Bhardwaj & Khanna, 2013; Lambert & Elias, 2010). Green tea catechins have proved to act as antioxidants by scavenging free radicals, inducing antioxidant enzymes or inhibiting pro-oxidant enzymes (Hou et al., 2005). Once a cup of green tea is consumed, the polyphenolic antioxidants are absorbed and enter the systemic circula- tion rapidly which causes a significant increase in plasma antioxidant capacity (Rein et al., 2012; Skrzydlewska, Ostrowska, Farbiszewski, & Michalak, 2002). But before absorption into the plasma, free or bound green tea catechins may show activity in the extracellular medium. Im- mediately after ingestion, green tea catechins may start to interact with dietary fiber bound antioxidant moieties like ferulic acid in any part of the body from mouth to colon. Ferulic acid, the major polyphenol found in cereals; especially in wheat bran, is placed in the cell walls of grains esterified with arabinoxylan units (Manach, Williamson, Morand, Scalbert, & Remesy, 2005). It may undergo a dimerization reaction itself in situ and may also be found as its dimer form, diferulic acid, which fortifies the insol- uble cell wall structure (Bunzel, Ralph, Marita, Hatfeld, & Steinhart, 2001; Wakabayashi, 2007). This kind of interaction may also take place between fiber bound ferulic acid and free soluble antioxidants in fluid phase. It was evidenced in our previous study that antioxidants bound to insoluble fiber matrix could be effectively regenerated in the presence of other hydrogen donating substances in liquid phase (Çelik, Gökmen, & Fogliano, 2013). This regeneration process might occur either through dimer formation or hydrogen atom transfer from soluble antioxidants to bound polyphenolic radicals. This study aimed to investigate the interaction between soluble an- tioxidants in green tea and insoluble dietary fiber bound antioxidants. Different concentrations of green tea catechins (infusions and pure Food Research International xxx (2014) xxx–xxx ⁎ Corresponding author. Tel.: +90 312 2977108. E-mail address: vgokmen@hacettepe.edu.tr (V. Gökmen). FRIN-05094; No of Pages 5 http://dx.doi.org/10.1016/j.foodres.2014.02.026 0963-9969/© 2014 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Food Research International journal homepage: www.elsevier.com/locate/foodres Please cite this article as: Çelik, E.E., & Gökmen, V., Investigation of the interaction between soluble antioxidants in green tea and insoluble dietary fiber bound antioxidants, Food Research International (2014), http://dx.doi.org/10.1016/j.foodres.2014.02.026