Impact of Bran Addition on Water Properties and Gluten Secondary Structure in Wheat Flour Doughs Studied by Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy

Abstract

The aim of this work was to elucidate the underlying physical mechanism(s) by which bran influences whole grain dough properties by monitoring the state of water and gluten secondary structure in wheat flour and bran doughs containing 35–50% moisture and 0–10% added bran. The system was studied with attenuated total reflectance (ATR) FTIR spectroscopy. Comparison of the OH stretch band of water in flour dough with that in H2O‐D2O mixtures having the same water content revealed the formation of two distinct water populations in flour dough corresponding to IR absorption frequencies at 3,600 and 3,200 cm–1. The band intensity at 3,200 cm–1, which is related to water bound to the dough matrix, decreased and shifted to lower frequencies with increasing moisture content of the dough. Addition of bran to the dough caused redistribution of water in the flour and bran dough system, as evidenced by shifts in OH stretch frequency in the 3,200 cm–1 region to higher frequencies and a reduction in monomeric water (free water). This water redistribution affected the secondary structure of gluten in the dough, as evidenced by changes in the second‐derivative ATR‐FTIR difference spectra in the amide I region. Bran addition caused an increase in β‐sheet content and a decrease in β‐turn (β‐spiral) content. However, this bran‐induced transconformational change in gluten was more significant in the 2137 flour dough than in Overley flour dough. This study revealed that when bran is added to flour dough, water redistribution among dough components promotes partial dehydration of gluten and collapse of β‐spirals into β‐sheet structures. This transconformational change may be the physical basis for the poor quality of bread containing added bran.

The structural evolution of water and gluten in refined and whole grain breads: A study of soft and hard wheat breads from postmixing to final product

“…Vector‐normalized H 2 O–D 2 O reference spectra of the same water content were digitally subtracted along with a vector‐normalized bran spectrum when appropriate. The difference spectra were subsequently analyzed in the 3,000–3,800 cm −1 region to detect shifts in the state and/or structure of water due to processing and bran addition (Bock et al, ; Bock & Damodaran, ; Jain, Varshney, & Maitra, ; Sutander, Ahn, & Franses, ; Zelent & Vanderkooi, ).…”

“…While most existing studies have focused on the secondary structural features of refined systems, there have been a few studies that have evaluated secondary structure in whole grain systems. Bock and Damodaran () and Bock et al () found the presence of bran altered water state and structure in model gluten and bread dough systems, consequently leading to an increase in β‐sheet structures at the expense of β‐turns and/or aperiodic structures. This was hypothesized to be partially responsible for the detrimental impact of bran in whole wheat bread.…”

“…The second reason is that it is difficult to give absolute secondary structural distributions for wheat gluten due to its high degree of polymorphism. It can generally be stated that the major structures in flour and dough include β‐sheets/β‐strands, β‐turns, aperiodic structures, and α‐helices in order of decreasing amount based on existing reports (Bock, Connelly, & Damodaran, ; Bock & Damodaran, ; Cao, Falk, & Bock, ). However, Cao et al () benchmarked the secondary structure of more than 30 individual wheat varieties in flour, dough, batter, and bread samples and noted a significant amount of variation in the ranges for different structures depending on the particular variety of wheat, moisture content, and degree of processing (i.e., mixing and baking).…”

Wheat milling by-products and their impact on bread making

“…Also the competition for water between meal constituents might explain the detrimental effect of wheat bran on bread properties. More recently, Bock, Connelly, and Damodaran (2013) observed a redistribution of water among dough components when wheat bran is added, resulting into partial dehydration and structural changes of the gluten proteins. A third possible explanation of the impact of bran on bread properties is its steric hindrance during dough development, disturbing the formation of an optimal gluten network (Gan, Ellis, Vaughan, & Galliard, 1989).…”

Conformational changes of polymers in model batter systems

“…Moreover in combination with new methods of sample presentation such as Attenuated Total Reflectance (ATR) e which enables analysis of food matrix directly in the solid or liquid state without further preparation e FTIR allows the acquisition of high-quality spectra with high reproducibility from previously quite intractable materials ( Van de Voort, Sedman, Emo, & Ismail, 1992;Wilson, Goodfellow, & Belton, 1988). ATR-FTIR spectroscopy has been used to probe gluten secondary structure in dough under various conditions and formulations Bock, Connelly, & Damodaran, 2013;Jazaeri et al, 2015;Kaddour et al, 2008;Li, Dobraszczyk, Dias, & Gil, 2006;Meziani et al, 2011;Sivam et al, 2012;Wang et al, 2014;Wellner et al, 2005). More recently, the poor quality of bran-enriched bread was explained by the conversion of b-turn structure into b-sheet and random structures when bran is added to the gluten or to wheat .…”