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 dough's 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 that the mechanical properties of the dough are sensitive to the presence of gas bubbles. At low void fractions, the elastic behavior of dough is also influenced by changes in dough matrix properties.

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Producing an aerated bread dough starts at the mixing stage where air bubble nuclei are incorporated into the dough. During fermentation, the production of CO 2 , due to yeast's metabolic activities, causes the bubbles to increase in size thereby increasing the volume and reducing the density. Therefore, the way in which the density of the dough is reduced and the dough's ability to retain gas plays an important part in the production of good loaf volume. A number of studies have used different approaches to examine the effects of fermentation conditions on the rheology of dough. The internal pressure of fermenting dough has been measured by placing the dough in a glass cylinder (Matsumoto et al 1971). The expansion of the dough resulting from fermentation was studied by Miller at al (1954), who measured the expansion by displacement of a weak salt solution. In another study (Marek and Bushuk 1966), the buoyancy of fermenting dough was measured by placing it on a balance in a constant temperature bath of mineral oil. However, despite the importance of dough density changes as an indicator of gas holding capacity of the dough, a direct comparison of how the density changes as the dough ferments using a variety of measurement techniques has not been reported.The objective of this note was to investigate the effect of measurement techniques on evaluation of dough density by measuring the decrease in density of fermenting dough under different geometrical constraints and comparing the results. To achieve this, the volume of the expanding dough was measured over time using three methods: 1) dough height increase within a graduated cylinder, 2) water displacement following free expansion of subsamples of the dough, and 3) radial expansion of dough constrained between two thick acrylic plates (measured using digital imaging). MATERIALS AND METHODSDough samples used in these experiments were prepared from Canadian Western Red Spring (CWRS) wheat flour by mechanical dough development using the standard Canadian Short Process Method (Preston et al 1982) as described by Elmehdi et al (2003). One mixed dough was used for a given dough density measurement technique, and three replicates were examined for each technique. At the end of mixing, subsamples were immediately removed from the dough piece. In the free expansion method, typically 20 subsamples were removed from the mixed dough, while for the other methods, only one subsample was required to perform the measurement. After measuring the mass of the subsample, it was placed in the apparatus used to measure the volume.For the free expansion method, the subsamples were placed in the proofing cabinet and the volume of the expanding dough was measured by taking one subsample at ≈5-min intervals. For all three methods, the apparatus and the subsample were placed in a proofing cabinet that was set at normal proofing conditions (37°C and 83% relative humidity) (Preston et al 1982). The change in the volume of the fermenting dough with time was then measured using one of the thr...

Purpose To probe the thermal and structural properties of gluten proteins using ultrasound. Methods A new ultrasonic approach for characterizing the quality of wheat gluten proteins is described. Low frequency (50 kHz) longitudinal ultrasonic velocity, v L , measurements were performed on gluten samples extracted from three wheat flours differing in protein content and in wheat endosperm hardness. Results At room temperature, v L for gluten extracted from soft flowers (Fielder) was found to be (870 ± 92) m/s, while for gluten extracted from extra strong flours (Glenlea) it was found to be (1,940 ± 90) m/s. In the second set of experiments, which aimed at probing thermal properties of gluten proteins, the variation in the numerical value of v L propagating in the wet gluten was found to be substantial (about 1,000 m/s) when the temperature of the gluten was raised from 20 to 90°C, and also when gluten from different flour types was investigated. A continuous structural phase transition was observed, which was different for glutens extracted from different flours. Upon cooling, the velocity also varied depending on wheat type. Conclusions These experiments demonstrate that ultrasonic velocity measurements can be used as a selection tool and study changes in properties of wheat proteins, particularly the thermal transitions that are critical to the quality of end products such as noodles, pasta, and bread. It was also shown that v L is sensitive to gluten class (strength or protein content), showing the potential of such measurements as an early-generation selection tool in wheat breeding programs.Keywords Ultrasound Á Gluten proteins Á Thermal transitions Á Quality Á Structure Riassunto Obiettivo Sondare le proprietà termiche e strutturali di proteine di glutine che usano l'ultrasuono. Materiali e Metodi Un nuovo approccio ultrasonico per caratterizzare la qualità di proteine di glutine di frumento è descritta. La frequenza bassa (50 kHz) la velocità longitudinale ultrasonica, il v L , le misure sono state eseguite sui campioni di glutine estratti da tre farine di frumento che differisce nel contenuto di proteina e nella durezza di endosperm di frumento. Risultati Alla temperatura ambiente, il v L per il glutine estratto dai fiori morbidi (l'Esterno) è stato trovato per essere (870 ± 92) il m/s, mentre per il glutine estratto dalle farine extra forti (Glenlea) è stato trovato per essere (1940 ± 90) il m/s. Nella seconda serie di esperimenti, che ha mirato a sondare le proprietà termiche di proteine di glutine, la variazione nel valore numerico di v L che propaga nel glutine bagnato è stata trovata per essere sostanzioso (circa 1000 m/s) quando la temperatura del glutine è stata alzata da 20 a 90°C ed anche quando il (2013( ) 16:101-110 DOI 10.1007 glutine dai tipi di farina diversi sono stati investigati. Una transizione di fase continua strutturale è stata osservata, che era diverso per i glutini estratti dalle farine diverse. Sul raffreddamento, la velocità il tipo di frumento di dipendere da anche var...

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