Application of FT-IR and Raman spectroscopy for the study of biopolymers in breads fortified with fibre and polyphenols A.S. Sivam a,b , D. Sun-Waterhouse a , C.O. Perera b , G.I.N. Waterhouse c, ⁎ a The New Zealand Institute for Plant & Food Research Limited, Food Innovation, Mt Albert Research Centre, Private Bag 92169, Auckland 1020, New Zealand b Food Science, Department of Chemistry, The University of Auckland, Auckland, New Zealand c Department of Chemistry, The University of Auckland, Auckland, New Zealand abstract article info Article history: Received 14 December 2010 Received in revised form 15 March 2011 Accepted 16 March 2011 Available online xxxx Keywords: Bread component interactions FT-IR spectroscopy Loop and Train model Pectins Polyphenols Raman spectroscopy Secondary protein conformation Adding dietary fibres (DFs) and polyphenols (PPs) to bread is a convenient way to deliver the health benefits of DFs and PPs to consumers. In this study, we investigate the interactions among added pectin polysaccharides, PPs and bread components such as wheat proteins in different bread formulations. Two sets of breads with a 20% difference in the water content were prepared in the absence (Control), or presence of pectin and/or fruit PP extracts (Treated). Results show that adding pectin and PPs caused changes in the molecular conformations and polymer structure of wheat gluten and starch in the finished breads, especially in the secondary protein conformation (Amides I and II, as revealed by FTIR Spectroscopy). An increase of water content during dough formulation also affected secondary protein conformation. The Treated breads gained β-sheets in the protein's secondary conformation at the expense of β-turns, and contained more un- ordered conformations especially in the presence of berry PPs. These results were confirmed by complementary Raman spectroscopic measurements. Both hydrophobic and H bonding interactions occurred among bread components and the added PPs and pectin, which affected PP stability during breadmaking and the total extractable PP content of finished breads. Schematic Loop and Train models for breads enhanced with PPs and pectin are proposed that illustrate the possible conformational changes in wheat protein structure due to the presence of added PPs and pectin. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Consumer demands for healthy diets and convenient foods create huge market potential for functional foods. Knowledge of the health benefits associated with increased consumption of polyphenols (PPs) and dietary fibre (DF) (Arts & Hollman, 2005; Schulze et al., 2004) has led to the inclusion of these active ingredients into popular consumer foods like bread (Brennan & Cleary, 2007; Sivam, Sun-Waterhouse, Perera, Quek, & Waterhouse, 2010; Sivam, Sun-Waterhouse, Waterhouse, Quek, & Perera, in press; Sun-Waterhouse, Chen, et al., 2009; Tiwari et al., 2011). Breadmaking is a complex process consisting of mixing, fermenta- tion, proofing and baking. During dough mixing, the mechanical energy imparted induces conformational changes in wheat proteins, such as breakage and formation of both covalent and non-covalent bonds e.g. hydrophobic and H bonds (Aït Kaddour, Barron, Robert, & Cuq, 2008). Baking involves heat and mass transfer, causing simultaneous physical, chemical and structural changes of bread components (Mondal & Datta, 2008; Tiwari et al., 2011). Baking also involves water evaporation, volume expansion, starch gelatinization, protein denaturation and crust formation (Manu & Prasad Rao, 2008). Water moves from hydrated gluten to starch granules resulting in the formation of H bonds via the three hydroxyl groups of the glycosyl residue of wheat starch (Ritota, Gianferri, Bucci, & Brosio, 2008). Wheat proteins undergo structural changes because of their heat susceptibility (Belton et al., 1995; Hayta & Schofield, 2004). Baking causes thermally induced protein denaturation (Falcão-Rodrigues, Moldão-Martins, & Beirão-da-Costa, 2005), and increased cross-linking and polymerization of gluten polymers due to increased sulfhydryl (SH) and disulphide (SS) interchange reactions (Lagrain, Brijs, Veraverbeke, & Delcour, 2005). FTIR and Raman spectroscopy are complementary vibrational spectroscopic techniques that allow the study of the chemical composition and molecular structure of heterogeneous foods and biological materials (Holse, Larsen, Hansen, & Engelsen, 2011; Yuen, Choi, Phillips, & Ma, 2009). These methods require very small amounts of sample (i.e. mg), are nondestructive and can be applied to study both dry and wet samples (Mauricio-Iglesais, Guillard, Gontard, & Peyron, 2009; Pereira, Amado, Critchley, van de Velde, & Ribeiro-Claro, 2009). IR and Raman spectroscopy are based on the changes in the electrical dipole moment and polarisability of chemical bonds, respectively (Pistorius, 1995), and thus yield different vibrational spectroscopic Food Research International xxx (2011) xxx–xxx ⁎ Corresponding author at: Department of Chemistry, The University of Auckland, 23 Symonds Street, Science Centre Building 301, Private Bag 92019, Auckland 1142, New Zealand. Tel.: + 64 9 3737599 87212. E-mail address: g.waterhouse@auckland.ac.nz (G.I.N. Waterhouse). FRIN-03628; No of Pages 12 0963-9969/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2011.03.039 Contents lists available at ScienceDirect Food Research International journal homepage: www.elsevier.com/locate/foodres Please cite this article as: Sivam, A. S., et al., Application of FT-IR and Raman spectroscopy for the study of biopolymers in breads fortified with fibre and polyphenols, Food Research International (2011), doi:10.1016/j.foodres.2011.03.039