Properties of bread dough and finished bread with added fibre polysaccharides and phenolic antioxidants

Abstract

Interests in incorporating bioactive ingredients such as dietary fibre (DF) and phenolic antioxidants into popular foods like bread have grown rapidly due to the increased consumer health awareness. The purpose of this study is to investigate the properties of breads enhanced with phenolic antioxidants and pectin fibres. To date, six papers have been published. Two sets of breads with a 20% difference in the water content were prepared in the absence (control bread), or presence of high methoxyl pectin (HM) and an apple, kiwifruit or blackcurrant polyphenol (PP) extract (APE, KPE or BPE treated bread). Breads were subjected to quality, chemical and rheological examinations. Fourier transform infra-red (FTIR) and Raman spectroscopy were used to explore the conformational changes in wheat proteins and polysaccharides in breads. Environmental Scanning Electron Microscopy (ESEM) and Cross Polarization/ Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance (CP/MAS 13C NMR) spectroscopy were used to examine the structural characteristics of bread polysaccharides, especially wheat starch in different bread formulations. A range of model breads containing flour, yeast, sugar, salt, oil and water, with or without added pectin and blackcurrant PP extract were examined to find out the extractability of PPs-protein complexes and their influence on the conformational structure of wheat proteins. The results revealed that added pectin and fruit phenolic extracts would lead to changes in bread appearance, quantity and composition of phenolic antioxidants in bread, and the rheological characteristics of bread dough and finished breads. Total extractable phenolic content (TEPC), antioxidant activity (AA), and HPLC results suggest that the ingredients used in bread formulation can induce various changes in secondary structure of wheat protein. HPLC- Mass (MS) spectrometry PP profiling revealed that baking caused oxidation of some added PPs such as quercetin and myricetin. SE-HPLC analysis showed that the free thiol groups in finished breads decreased with an elevated percentage of the Unextractable High Molecular Weight (UHMW) proteins. As per FTIR and Raman spectroscopy results adding pectin and PPs caused changes in conformations and polymer structure of wheat gluten and wheat starch. Analyses of the model formulations revealed that adding PPs increased the TEPC and AA of the baked breads. The formation of HMW aggregated gluten proteins occurred in the absence of added PPs and pectin. The addition of PPs and pectin decreased the proportion of UHMW proteins suggesting the occurrence of protein solubilisation. Replacing flour with starch and gluten caused a reduction in the TEPC, AA, the amounts of BPE’s anthocyanins especially delphinidin-3-o-glucoside and delphinidin-3- o-rutinoside, and lowered the intensity of the Amide I band, and led to the disappearance of the Amide II band. CP/MAS 13C NMR studies revealed differences in amylopectin-related crystalline domains and the amylose-related amorphous domains among the breads. All breads showed V-type or amorphous starch structures; however the control bread contained some of A-type starch. Breads formulated with 20% extra water showed a greater degree of starch gelatinisation, a smoother crumb microstructure and a lower amorphous starch content. The differences in the microstructure of starch/protein matrix in the finished breads revealed by ESEM and optical microscopy supported the NMR findings. In conclusion, the added pectin, PPs and possibly the oxidation products of PPs affected the interactions between water and bread components. Wheat proteins and starch during dough development and bread baking caused differences in cross-linked microstructures. These interactions ultimately affected the extractability and/or stability of added PPs. Both the composition of a recipe and the order of ingredient addition influenced the properties of the model bread systems