Application of FT-IR and Raman spectroscopy for the study of biopolymers in breads fortified with fibre and polyphenols

Abstract

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.