Pulse Flour Characteristics from a Wheat Flour Miller's Perspective: A Comprehensive Review.

Pulses (grain legumes) are increasingly of interest to the food industry as product formulators and consumers seek to exploit their fiber-rich and protein-rich reputation in the development of nutritionally attractive new products, particularly in the bakery, gluten-free, snack, pasta, and noodle categories. The processing of pulses into consistent high-quality ingredients starts with a well-defined and controlled milling process. However, in contrast to the extensive body of knowledge on wheat flour milling, the peer-reviewed literature on pulse flour milling is not as well defined, except for the dehulling process. This review synthesizes information on milling of leguminous commodities such as chickpea (kabuli and desi), lentil (green and red), pea, and bean (adzuki, black, cowpea, kidney, navy, pinto, and mung) from the perspective of a wheat miller to explore the extent to which pulse milling studies have addressed the objectives of wheat flour milling. These objectives are to reduce particle size (so as to facilitate ingredient miscibility), to separate components (so as to improve value and/or functionality), and to effect mechanochemical transformations (for example, to cause starch damage). Current international standards on pulse quality are examined from the perspective of their relationship to the millability of pulses (that is, grain legume properties at mill receival). The effect of pulse flour on the quality of the products they are incorporated in is examined solely from the perspective of flour quality not quantity. Finally, we identify research gaps where critical questions should be answered if pulse milling science and technology are to be established on par with their wheat flour milling counterparts.

Transmission of ultrasound through a single layer of bubbles.

We investigate, both experimentally and theoretically, the effect of coupling between resonant scatterers on the transmission coefficient of a model system of isotropic scatterers. The model system consists of a monodisperse layer of bubbles, which exhibit a strong monopole scattering resonance at low ultrasonic frequencies. The layer was a true 2D structure obtained by injecting very monodisperse bubbles (with radius a approximately 100 microm) into a yield-stress polymer gel. Even for a layer with a low concentration of bubbles (areal fraction, n pi a(2), of 10-20%, where n is the number of bubbles per unit area), the ultrasonic transmission was found to be significantly reduced by the presence of bubbles (-20 to -50 dB) and showed a sharp minimum at a particular frequency. Interestingly, this frequency did not correspond to the resonance frequency of the individual, isolated bubbles, but depended markedly on the concentration. This frequency shift is an indication of strong coupling between the bubbles. We propose a simple model, based on a self-consistent relation, which takes into account the coupling between the bubbles and gives good agreement with the measured transmission coefficient.

Bubbles in noodle dough: Characterization by X-ray microtomography.

Bubbles, found in a huge variety of food products, are known to afford desirable quality attributes, especially those related to texture, mouthfeel and taste. However, the presence of bubbles and their effects on wheat flour noodles is an aspect that has been, until now, largely overlooked, despite the positive and negative connotations of bubbly inclusions on Asian noodle quality. X-rays from a synchrotron source (Biomedical Imaging and Therapy facility at the Canadian Light Source) were used to rapidly and non-destructively acquire tomographic images of noodle dough. Appropriate image analysis protocols were used to determine the bubble size distribution, the orientation of bubbles, and their position within the dough sheet. The effect of processing (one or multiple lamination steps) on bubble properties in the dough that was subsequently sheeted (gradual elongation and reduction in thickness) was investigated. Bubble size distributions, well captured by lognormal distribution function, showed that the lamination process induced bubble entrapment and reduction in bubble size. Bubbles were found to be flat, elongated and oriented in the sheeting direction, this effect being less for doughs laminated ten times (90° rotations between lamination steps). Interestingly, a gradient in concentration of bubbles within the dough sheet was found from the noodle core to the sheet edges. Aging effects were also apparent. This first non-destructive study of bubbles in wheat-flour noodle dough provides a more complete knowledge of the dough sheet's internal structure, and how it originates via processing, and this has repercussions on the overall quality of Asian noodles.

Characterizing a model food gel containing bubbles and solid inclusions using ultrasound.

Ultrasonic spectroscopy is used to characterize a model aerated food system consisting of agar gel in which both bubbles and polystyrene beads are embedded. By exploiting the distinct frequency dependence of each inclusion's acoustic resonances, it is demonstrated that the sizes of the bubbles and beads can be measured by ultrasound even when the size distributions are so similar that these inclusions are difficult to distinguish in optical images. While these results demonstrate the potential for applying ultrasonic spectroscopy to evaluate any soft heterogeneous material in which both bubbles and solid inclusions are present, the technique is especially relevant for functional foods, in which solid functional ingredients must be incorporated without degrading the aerated structure of the food and causing unacceptable quality impairment.

Development of emulsifying property in Persian gum using octenyl succinic anhydride (OSA).

In the present study, the influence of octenyle succinic anhydride (OSA),gum concentration, pH, temperature and reaction time on esterification of Persian gum (PG), and its soluble (SFPG) and insoluble (IFPG) fractions, were investigated by response surface methodology (RSM) in order to optimize the reaction conditions based on the degree of substitution (DS). The individual effect of all independent variables as well as the interactive effects of temperature-OSA concentration, and OSA-PG concentrations on DS was significant. However, the latter interactive effect (OSA-SFPG) was not significant in case of SFPG. The IFPG did not have any esterification reaction with OSA. The highest DS for PG and SFPG were 0.0285 and 0.0303 at the optimal conditions, respectively. The FTIR spectrums also confirmed the carbonyl group attachment in OSA-PG and OSA-SFPG. The enhancement of emulsifying capability was also confirmed by ECI and EAI values, microscopic images as well as rheological measurements.

Influence of internal interfacial area on nanosecond relaxation of wheat gluten proteins as probed by broadband ultrasonic spectroscopy.

Understanding interactions between interfaces and biopolymers in complex industrially processed materials of plant origin will allow for their better utilization. Wheat flour doughs are one such material whose industrial use strongly depends on such interactions due to their effect on the mechanical properties of the dough. To date, mechanical characterizations of dough have been limited to a narrow range of frequencies. Here, ultrasonic spectroscopy measurements over a very broad frequency range are used to show that a fast volumetric relaxation occurs in dough; the nanosecond timescale of the relaxation is associated with ultrasonic stress-induced changes in the secondary structure of gluten proteins. Interestingly, there is a four-fold difference in the speed of this relaxation phenomenon in doughs mixed in air (where substantial internal interfacial area exists) compared to those mixed under vacuum (where bubbles are absent). Given the large internal interfacial area in dough, the amphiphilic proteins residing at gas bubble interfaces significantly alter the high-frequency mechanical response of this important material.

Probing thermal transitions and structural properties of gluten proteins using ultrasound.

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.

Ultrasonic investigation of the effect of vegetable shortening and mixing time on the mechanical properties of bread dough.

Mixing is a critical stage in breadmaking since it controls gluten development and nucleation of gas bubbles in the dough. Bubbles affect the rheology of the dough and largely govern the quality of the final product. This study used ultrasound (at a frequency where it is sensitive to the presence of bubbles) to nondestructively examine dough properties as a function of mixing time in doughs prepared from strong red spring wheat flour with various amounts of shortening (0%, 2%, 4%, 8% flour weight basis). The doughs were mixed for various times at atmospheric pressure or under vacuum (to minimize bubble nucleation). Ultrasonic velocity and attenuation (nominally at 50 kHz) were measured in the dough, and dough density was measured independently from specific gravity determinations. Ultrasonic velocity decreased substantially as mixing time increased (and more bubbles were entrained) for all doughs mixed in air; for example, in doughs made without shortening, velocity decreased from 165 to 105 ms(-1), although superimposed on this overall decrease was a peak in velocity at optimum mixing time. Changes in attenuation coefficient due to the addition of shortening were evident in both air-mixed and vacuum-mixed doughs, suggesting that ultrasound was sensitive to changes in the properties of the dough matrix during dough development and to plasticization of the gluten polymers by the shortening. Due to its ability to probe the effect of mixing times and ingredients on dough properties, ultrasound has the potential to be deployed as an online quality control tool in the baking industry.

Extrusion of pea starch containing lysozyme and determination of antimicrobial activity.

Pea starch, which has inherently good gel strength, was used as the source material for manufacturing a biodegradable and bioactive packaging material. Extrudates containing 99% pea starch and 1% lysozyme were produced under various extrusion conditions (high and low shear screw configurations, 30% to 40% moisture contents, 70 to 150 degrees C die temperatures). The physical and mechanical properties of the extrudates were determined through various expansion indices, piece and cell wall solid density, compression, and 3-point bending tests. The expansion of extrudates increased with an increase in die temperature, whereas increasing moisture content had the opposite effect. Extrudate densities decreased as extrusion temperature increased, whereas lower moisture content in the extrudate dough decreased extrudate densities. The elastic modulus and fracture strengths were highly correlated in a power-law fashion to relative density, showing that the mechanical properties of extrudates were dependent on solid density and foam structure. Up to 48% of the initial lysozyme activity was recovered from the extruded pea starch matrix. The lysozyme released from extrudates showed an inhibition zone against Brochotrix thermosphacta B2. Extruded pea starch matrix containing lysozyme has potential application as an edible and biodegradable packaging material with antimicrobial activity.