Martin G. Scanlon

Bread properties and crumb structure

Abstract The relationship between bread-crumb cellular structure and many aspects of quality in a loaf of white bread justifies investigations of how the structure arises during processing of the dough. Following a brief overview of the development of bread cellular structure in the dough, three parts of the literature pertaining to crumb appearance (visual texture) and bread quality are reviewed, with emphasis on the mechanical properties (physical texture) of the crumb. The importance of an objective segmentation of the two macroscopic phases (crumb cells and cell walls solids) is emphasised in digital image analysis studies of bread-crumb structure. A review of studies where mechanical properties have been measured in fundamental units has sections on the mechanical properties of the composite structure and on recent analyses of the mechanical properties of the solid phase. Finally, models which have been used to relate structure to mechanical properties will be reviewed with emphasis on the work of Gibson and Ashby [Gibson, L.J., & Ashby, M.F., 1988. Cellular solids: structure & properties. Oxford: Pergamon Press; Gibson, L.J., & Ashby, M.F., 1997. Cellular solids: structure and properties (2nd ed.). Cambridge: University Press]. It is shown that experimental values of Youngs modulus of bread crumb reside within the Hashin-Shtrikman bounds. Compared with the rule of mixtures, these bounds represent a good (52%) improvement in the ability to predict values for bread crumb moduli (crumb firmness). Using information provided by digital image analysis, Gibson and Ashbys relationships between structure (relative density) and mechanical properties can be modified to incorporate dough processing effects such as dough strain hardening and the effect of gas cell coalescence.

Relationship of creep-recovery and dynamic oscillatory measurements to durum wheat physical dough properties

ABSTRACT Durum wheat gluten strength is important in determining extrusion properties and pasta cooking quality. Durum wheats varying in strength were tested using an alveograph and a 2-g micro-mixograph, both widely accepted techniques for determination of physical dough properties. Doughs from the 2-g micro-mixograph were characterized by dynamic oscillatory and large deformation creep tests using a controlled stress rheometer. Mechanical properties obtained from both testing regimes were strongly correlated with many of the parameters provided by the alveograph and micro-mixograph. Maximum strain attained after 5 min creep ranged from 25% for the weakest cultivar, with a coefficient of variation among replicates of 16,000 Pa for the strongest, least extensible cultivars, with a coefficient of variation of ...

Prediction of Bread Crumb Density by Digital Image Analysis

ABSTRACT The cellular structure of bread crumb (crumb grain) is an important factor that contributes to the textural properties of fresh bread. The accuracy of a digital image analysis (DIA) system for crumb grain measurement was evaluated based on its capability to predict bread crumb density from directly computed structural parameters. Bread was prepared from representative flour samples of two different wheat classes, Canada Western Red Spring (CWRS) and Canada Prairie Spring (CPS). Dough mixing and proofing conditions were varied to manipulate loaf volume and crumb density. Sliced bread was subjected to DIA immediately after physical density measurement. Experiments were repeated for the same bread samples after drying to three different moisture contents. Five computed crumb grain parameters were assessed: crumb brightness, cell wall thickness (CWT), void fraction (VF), mean cell area, and crumb fineness (measured as number of cells/cm2). Crumb density ranged from 0.088 to 0.252 g/cm3 depending on p...

Role of Gluten and Its Components in Determining Durum Semolina Dough Viscoelastic Properties

ABSTRACT Gluten was isolated from three durum wheat cultivars with a range in strength. Gluten was further fractionated to yield gliadin, glutenin and high molecular weight (HMW) and low molecular weight (LMW) glutenin subunits (GS). The gluten and various fractions were used to enrich a base semolina. Enriched dough samples were prepared at a fixed protein content using a 2-g micromixograph. Mixing strength increased with addition of gluten. Dynamic and creep compliance responses of doughs enriched with added gluten ranked in order according to the strength of the gluten source. Gliadin addition to dough resulted in weaker mixing curves. Gliadin was unable to form a network structure, having essentially no effect on dough compliance, but it did demonstrate its contribution to the viscous nature of dough (increased tan δ). Source of the gliadin made no difference in response of moduli or compliance. Addition of glutenin to the base semolina increased the overall dough strength properties. Glutenin source ...

Effects of Flour Strength, Baking Absorption, and Processing Conditions on the Structure and Mechanical Properties of Bread Crumb

ABSTRACT The objective of this study was to determine the effects of flour type, baking absorption, variation in sheeting, and dough proofing time on the density, crumb grain (visual texture), and mechanical properties (physical texture) of bread crumb. All response variables were measured on the same bread crumb specimens. Bread loaves were prepared by a short-time bread-making process using four spring wheat flours of varying strength. After crumb density measurement, digital image analysis (DIA) was used to determine crumb grain properties including crumb brightness, cell size, cell wall thickness, and crumb uniformity. Tensile tests were performed on bone-shaped specimens cut from the same bread slices used for DIA to obtain values for Youngs modulus, fracture stress, fracture strain, and fracture energy. Proof time had the most profound influence on the bread with substantial effects on loaf volume, crumb density, crumb brightness, and grain, as well as crumb mechanical properties. Increasing proof ...

Monitoring Dough Fermentation Using Acoustic Waves

Fermentation of the sugars in bread dough produces carbon dioxide which diffuses through the dough matrix into the gas cell nuclei formed during dough mixing. As a result, the void fraction of the dough increases and dough density decreases. It is shown in this paper that low intensity ultrasound can be used to monitor changes in the void fraction of this opaque material, thus providing real-time information on changes in the structure of the dough during fermentation. Doughs were mixed under two different mixer headspace conditions, and the ultrasonic velocity and attenuation measured as a function of fermentation time. The results of the ultrasonic experiments were compared with changes in dough density (measured independently but under the same experimental conditions). As fermentation time increased (and gas cells expanded), the ultrasonic velocity decreased and the attenuation increased. At early fermentation times, a substantial drop in velocity was observed before the density changed appreciably, indicating that yeast activity has two independent effects on dough properties: modifying the elasticity of the dough matrix and expanding the gas cells. Ultrasound therefore has the potential to provide novel information on technological issues of critical importance to the cereals’ processing industry.

Sound velocity and attenuation in bubbly gels measured by transmission experiments

Measurements of the phase velocity and attenuation of sound in concentrated samples of bubbly gels are presented. Hair gel was used as a matrix material to obtain well characterized distributions of bubbles. Ultrasonic measurements were conducted over a large range of frequencies, including the resonance frequencies of the bubbles. Surprisingly good agreement with Foldys prediction was found, even for monodisperse samples at resonance frequencies, up to volume fraction of 1%. Beyond this concentration, the effects of high-order multiple scattering were observed. These results support the feasability of ultrasonic techniques to investigate the size distribution of bubbles in a weak gel or liquid.

Starch Participation in Durum Dough Linear Viscoelastic Properties

ABSTRACT The contribution of starch to dough rheological properties has been largely overshadowed by the role of gluten, receiving much less attention in comparison. The influence of starch granule surface properties on durum wheat dough linear viscoelasticity was investigated, and surface interactions between starch granules and gluten were assessed using a model system. Proportions of starch were substituted in dough on a volume basis with an inert filler (glass powder) with a similar particle size range. The doughs were subjected to dynamic and creep measurements. Dough linear viscoelastic properties were weakened on substitution of starch with glass powder at ≤50% substitution, inferring a reduction in adhesion at the matrix-filler (starch and glass powder) interface with declining proportions of starch granules. Surface modification of starch granules or glass powder altered dough rheological properties, confirming the importance of starch granule surface characteristics and the nature of protein-sta...

Effect of tempering and end moisture content on the quality of micronized lentils

The use of micronization (infrared treatment) on grain legumes tempered with water has potential for reducing cooking times. Using Laird lentils, the effects of tempering conditions and moisture content following micronization were evaluated in terms of color, chemical properties and texture after 15 min cooking. The texture of cooked lentils softened as tempering moisture increased. This was related to increasing starch gelatinization and decreasing protein solubility during micronization. Changes in the pectic substances did not appear to influence texture. The reduction in hardness indicates that shorter cooking times are required for samples micronized under high moisture conditions. Lentil color changed slightly under these high moisture conditions as evidenced by the Hunterlab readings.

Ultrasonic Investigation of the Effect of Mixing Under Reduced Pressure on the Mechanical Properties of Bread Dough

ABSTRACT Mixing is critical to attainment of a desirable gas cell distribution in dough. By varying mixer headspace pressure, changes in the mechanical properties of dough were investigated as a function of the doughs void concentration using low frequency (50 kHz) ultrasonic techniques. For the mixer used, this allowed the volume fraction of voids (Φ) to be varied from ≈0.01 to 0.08. The ultrasonic attenuation of longitudinal waves increased linearly with increases in Φ. If, as reported, pressure reductions during mixing decrease the number density of the voids but do not affect void size, the change in attenuation is proportional to the number of voids. By contrast, the velocity of longitudinal ultrasonic waves decreased dramatically with increasing Φ in the range 0.012 < Φ < 0.03, dropping from a value near that of water to values well below the velocity of sound in air. At higher Φ, the velocity decrease was less rapid. The longitudinal elastic modulus determined from these ultrasonic results shows t...