Jana van Rooyen

Background and Objectives: Dry thermal treatment of wheat modifies the properties of wheat and of flour prepared from it. The objective of this study was to investigate the effect of wheat roasting on microstructural properties of wheat grains using confocal laser scanning, X‐ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. The impact of roasting on the damaged starch contents, the solvent retention capacity profiles, and the pasting properties of the resulting flour prepared from roasted wheat were also studied. Findings: Response surface models predicted wheat roasting at 115°C and 65 Hz (165 s) to enhance flour viscosifying properties. Roasting before milling resulted in grain puffing, slight damage to the starch granule surface, and destruction of the protein matrix, as observed using SEM. XRD analysis revealed that amylose–lipid complexation had occurred. As a result of roasting, the peak, hot paste, and final viscosities of flour from roasted wheat were significantly ( p ≤ .05) higher than those of flour produced from control wheat. Conclusions: Roasting induces structural changes in wheat. Flour produced from roasted wheat can be used to produce gel structures with increased viscosities. Significance and Novelty: Dry thermal treatment improves the viscosifying properties of flour milled from roasted wheat.

Background and Objectives: In the accompanying paper (Part 1), it was reported that forced convection roasting of wheat before milling can be directed to tailor the viscosifying properties of flour. The objective of the present work was to examine the effect of prior wheat roasting on flour proteins. Findings: Effective control of wheat roasting conditions proved to be essential to avoid the irreversible loss of flour functionality as deduced from the flour ethanol and lactic acid solvent retention capacity and mixography data. Response surface models predicted roasting at 108°C and 80 Hz (135 s) to maintain protein integrity. The microstructure of flour and isolated starch as well as X‐ray diffraction patterns revealed starch to be relatively unaffected by this heat treatment. Conclusions: Flour produced from roasted wheat can still be used for products that require the formation of a gluten network. Significance and Novelty: Protein is more sensitive to roasting conditions than starch.

Bread dough and bread are dispersed systems consisting of starch polymers that interact with other flour components and added ingredients during processing. In addition to gluten proteins, starch impacts the quality characteristics of the final baked product. Wheat starch consists of amylose and amylopectin organized into alternating semicrystalline and amorphous layers in granules that vary in size and are embedded in the endosperm protein matrix. Investigation of the molecular movement of protons in the dough system provides a comprehensive insight into granular swelling and amylose leaching. Starch interacts with water, proteins, amylase, lipids, yeast, and salt during various stages of breadmaking. As a result, the starch polymers within the produced crumb and crust, together with the rate of retrogradation and staling due to structural reorganization, moisture migration, storage temperature, and relative humidity determines the final product's textural perception. This review aims to provide insight into wheat starch composition and functionality and critically review recently published research results with reference to starch structure–function relationship and factors affecting it during dough formation, fermentation, baking, cooling, and storage of bread.

Heat treatment is used as a pre-processing step to beneficially change the starch properties of wheat flour to enhance its utilisation in the food industry. Heat-treated wheat flour may provide improved eating qualities in final wheat-based products since flour properties predominantly determine the texture and mouthfeel. Dry heat treatment of wheat kernels or milled wheat products involves heat transfer through means of air, a fluidising medium, or radiation—often resulting in moisture loss. Heat treatment leads to changes in the chemical, structural and functional properties of starch in wheat flour by inducing starch damage, altering its molecular order (which influences its crystallinity), pasting properties as well as its retrogradation and staling behaviour. Heat treatment also induces changes in gluten proteins, which may alter the rheological properties of wheat flour. Understanding the relationship between heat transfer, the thermal properties of wheat and the functionality of the resultant flour is of critical importance to obtain the desired extent of alteration of wheat starch properties and enhanced utilisation of the flour. This review paper introduces dry heat treatment methods followed by a critical review of the latest published research on heat-induced changes observed in wheat flour starch chemistry, structure and functionality.