Dough Matrix Research Articles

Harvesting yeast (Saccharomyces cerevisiae) at different physiological phases significantly affects its functionality in bread dough fermentation

Fermentation of sugars into CO2, ethanol and secondary metabolites by baker's yeast (Saccharomyces cerevisiae) during bread making leads to leavening of dough and changes in dough rheology. The aim of this study was to increase our understanding of the impact of yeast on dough related aspects by investigating the effect of harvesting yeast at seven different points of the growth profile on its fermentation performance, metabolite production, and the effect on critical dough fermentation parameters, such as gas retention potential. The yeast cells harvested during the diauxic shift and post-diauxic growth phase showed a higher fermentation rate and, consequently, higher maximum dough height than yeast cells harvested in the exponential or stationary growth phase. The results further demonstrate that the onset of CO2 loss from fermenting dough is correlated with the fermentation rate of yeast, but not with the amount of CO2 that accumulated up to the onset point. Analysis of the yeast metabolites produced in dough yielded a possible explanation for this observation, as they are produced in different levels depending on physiological phase and in concentrations that can influence dough matrix properties. Together, our results demonstrate a strong effect of yeast physiology at the time of harvest on subsequent dough fermentation performance, and hint at an important role of yeast metabolites on the subsequent gas holding capacity.

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

ABSTRACTThe 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.

What Has Low-Intensity Ultrasound Informed Us about Wheat Flour Dough Rheology?

The role of rheology in understanding the process behavior of dough and its predictive capacity with respect to breadmaking quality is of long-standing interest to cereal scientists. Over the past 12 years, we have undertaken a comprehensive examination of the rheology of wheat flour doughs using low-intensity ultrasound. Propagating shear waves at ultrasonic frequencies in conjunction with small-strain shear rheometry allowed us to show how a very broad distribution of relaxation times is necessary to define the complex shear modulus of wheat flour dough. When propagating longitudinal ultrasonic waves, three distinct regions are seen in the ultrasonic spectrum arising from the presence of bubbles in the dough. At low frequencies, where the properties of the bubbles–dough matrix “composite” are probed, the rheology of air-mixed doughs contrasts markedly with that of doughs mixed under vacuum. Therefore, all dough rheology is affected by the bubbles within the dough.

2D structural imaging study of bubble evolution during leavening

Invasive, continuous measurements on dough are generally not adequate as they may provoke dough collapse. The choice of the most appropriate analytical procedure is thus crucial for the full comprehension of the underlying mechanisms of leavening.The purpose of this investigation was to present an analytical approach based on image analysis to describe how bubbles grow in wheat flour dough during leavening.The leavening kinetic was investigated by monitoring the variation of morphology descriptors of dough vs time. The digital image analysis procedures allowed to determine interpretable parameters of bubble evolution during leavening including dough area, bubble area, bubble wall roundness, the number of gas bubbles and the bubble size distributions. The kinetic of volume had sigmoid shape with 2.7 as asymptotic value. A modified Gompertz model was chosen as descriptive model of the leavening stage. Quite good agreement was observed between experimental data and model parameters (R2 greater than 0.99).Results demonstrate that the changes in morphology descriptors provide insight into how gas bubbles in the dough matrix can be formed during dough processing. The average area bubble grew from 0.27mm to 1.5mm and the average roundness changed from 1.3 to 1.6. Experimental bubble size distributions were presented and discussed.

Fermentation responses and in vitro radical scavenging activities of Fagopyrum esculentum

In this study, the impact of fermentation of Fagopyrum esculentum (buckwheat) by Lactobacillus delbrueckii subsp. lactis was investigated. The interaction between starter culture and buckwheat dough matrix was evaluated with respect to microbial count, final pH, organic acids, total phenolic content and antioxidant potential. An increase of one log cycle from 8.76 to 9.92 log CFU(Colony Forming Unit)/g was observed during fermentation. Lactic acid content increased up to 1350 μg/g within 24 h of fermentation. The most significant result of this study was an observed increase in the total phenolic content of the dough, from 2.73 to 7.64 mg GAE(Gallic Acid Equivalence)/g. Antioxidant potential of fermented buckwheat also showed an increased percentage of 2,2-diphenyl-2-picrylhydrazyl scavenging activity from 44.32% to 88.98% and ferric reducing antioxidant power potential increased from 14.43 to 25.68 μM Fe(II)/g after 72 h of fermentation. We conclude that lactic acid fermentation of buckwheat dough has a potential to be a functional food, with enhanced antioxidant activity.

Functional Properties of Gluten-Free Pasta Produced from Amaranth, Quinoa and Buckwheat

The use of amaranth, quinoa and buckwheat for the production of gluten-free pasta was investigated in the present study. The aim of the work was to produce pasta of good textural quality, in particular, low cooking loss, optimal cooking weight and texture firmness. The results demonstrated that pasta produced from amaranth had decreased texture firmness and cooking time, while pasta from quinoa mainly showed increased cooking loss. In buckwheat pasta the least negative effects were observed. By combination of all three raw materials to one flour blend in the ratio of 60% buckwheat, 20% amaranth and 20% quinoa, dough matrix was improved. After decreasing dough moisture to 30%, addition of an increased amount of egg white powder of 6% and addition of 1.2% emulsifier (distilled monoglycerides) texture firmness as well as cooking quality of gluten-free pasta produced from such a flour blend reached acceptable values comparable to wheat pasta.

Physical characterization of fiber-enriched bread doughs by dual mixing and temperature constraint using the Mixolab®

Dietary fiber incorporation into bread dough systems greatly interferes with protein association and behavior during heating and cooling. The objective of this study was to understand the individual and combined effects of dietary fibers on dough behavior during mixing, overmixing, pasting and gelling using the Mixolab® device. Impact of different commercial dietary fibers (inulin, sugar beet fiber, pea cell wall fiber and pea hull fiber) on wheat dough mixing, pasting and gelling profiles has been investigated. Mixolab® plots indicate that the incorporation of sugar beet fiber into the dough matrix induces the disruption of the viscoelastic system yielding weaker doughs, and it greatly competes for water with starch affecting pasting and gelling. Conversely, inulin in the range tested seems to integrate into the dough increasing its stability. Additionally, the responses acquired with this device were compared with those obtained with other available methodologies, such as the Brabender Farinograph and the Rapid Visco Analyser, to explore its use as a suitable technique for studying fiber-enriched bread dough physical properties. A broad range of correlation between Mixolab® and traditional devices were found.

Effect of wheat dietary fibres on bread dough development and rheological properties

Several fractions of wheat fibres were isolated from starchy endosperm, aleurone layer and bran, and characterized for their hydration properties and arabinoxylans (AX) content. The influence of their addition, up to 10%, to standard flour was studied through mixing tests, and rheological tests at small and large deformations. The effect of insoluble AX on dough development was accounted for by their capacity to retain water, whatever their origin and percentage of addition. The addition of insoluble AX increased the viscoelastic plateau modulus. The addition of soluble and insoluble AX to the dough did not modify the overall dough flow behaviour in shear, characterized by a Newtonian plateau at low shear rates followed by shear-thinning behaviour at larger shear rates. This behaviour could be fitted by the Cross model. The addition of water soluble AX modified the Newtonian viscosity value. Conversely, the addition of insoluble ones increased dough consistency, probably through a filler-like effect in the dough matrix.

Selectivity for water-unextractable arabinoxylan and inhibition sensitivity govern the strong bread improving potential of an acidophilic GH11 Aureobasidium pullulans xylanase

An acidophilic xylanase of Aureobasidium pullulans (XAPI) was recombinantly produced, characterised and its functionality in bread making compared with that of Bacillus subtilis Xyn A xylanase (XBS), an enzyme frequently used in bread making. Prominent characteristics of XAPI were its high specific activity towards arabinoxylan (AX), its relative preference for hydrolysis of water-unextractable AX (WU-AX), its optimal activity under acidic conditions and its sensitivity towards TAXI ( Triticum aestivum xylanase inhibitor) and XIP (xylanase inhibiting protein). Optimally developed dough containing XAPI had a considerably drier feel after mixing and was less sticky after fermentation than dough treated with XBS. Both xylanases improved bread loaf volume by 24% under the conditions of the process. In spite of the higher dosage of XAPI necessary to obtain this result, the similar loaf volume increase coincided with less solubilisation of WU-AX and even lesser degradation of solubilised AX (S-AX) and water-extractable AX (WE-AX) by XAPI than by XBS during the bread making process. This is probably due to different dynamics and extent of xylanase inhibition in the dough matrix for both xylanases. AX solubilisation by the acidophilic XAPI was not boosted by the drop in pH in the dough during fermentation. Results show that significant bread loaf volume increase goes hand in hand with excellent dough properties when a limited solubilisation of WU-AX during mixing is coupled to retention of a high molecular mass of S-AX and WE-AX during the rest of the process.

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.

Structural enhancement leading to retardation of in vitro digestion of rice dough in the presence of alginate

The effect of alginate with distinct content of guluronate sequences on the structural properties and in vitro digestion of rice dough has been investigated. Materials were engineered to serve as a model system of instant soup-based rice noodles available in the market. Alginate set externally with calcium within the dough matrix reduced cooking loss and soluble starch leakage following boiling of preparations. Small-deformation dynamic-oscillation monitored the structural properties of alginate networks, which were capable of supporting the starch granules in a cohesive composite gel. Scanning electron microscopy afforded tangible evidence of the dramatic effect of the polysaccharide network on the morphology of rice dough. Fourier transform infrared spectroscopy probed at the molecular lever the efficiency of external setting to deliver calcium ions at the vicinity of the carboxyl groups of the alginate chain. It appears that the continuous alginate phase encapsulates starch granules thus retarding in vitro digestion of the rice dough. Results are promising for the development of commercial rice noodles with superior appearance, textural profile and digestibility.

Wheat Proteins Extracted from Flour and Batter with Aqueous Ethanol at Subambient Temperatures

ABSTRACTContact of wheat flour with aqueous ethanol may enrich protein by starch displacement or deplete protein by extraction depending on 1) extraction conditions and 2) the form of the substrate. Extraction at subambient temperatures has not been described for specific gliadins for either dry flour with the protein in native configurations or for wet, developed batter or dough. This limits the ability to interpret technologies such as the cold‐ethanol method. Here, we describe specific albumin and gliadin composition of flour extracts by capillary zone electrophoresis CZE in 0–100% (v/v) ethanol from –12 to 22°C. Extraction was reduced for albumin and gliadin protein as the temperature was reduced and the concentration range for extraction narrowed. Extraction dropped precipitously between 0 and –7°C for both albumins and gliadins. Electrophoretically defined gliadins extracted in constant proportion at 22°C and 30–80%(v/v) ethanol, but at lower temperature, the α‐gliadins were enriched and β‐gliadins depleted in the 30–55% (v/v) range. For extracts from wheat flour batter, depletion of α and β and enrichment of γ relative to the dry flour contact suggested that the electrophoretically slow migrating γ‐ and ω‐proteins are less well incorporated to the dough matrix than electrophoretically fast migrating α and β types.

Influence of starch addition and dough microstructure on fermentation aroma production by yeasts and lactobacilli

The work hypothesis of this paper was that during fermentation processes the chemico-physical interactions of the microbial metabolites with food matrix affects not only their retention, but the metabolic activity of the microorganisms. The influence of starch addition to liquid fermentation systems simulating sourdough and inoculated with pure and mixed population of Saccharomyces cerevisiae, Candida milleri and Lactobacillus sanfranciscensis significantly enhanced the production of selected metabolites. Moreover the starch addition interfered with the response of S. cerevisiae, C. milleri and L. sanfranciscencis when exposed to conditioned media of L. sanfranciscensis resulting in an increasing production of alcohols, isovaleric acid and of a key odorant like γ-decalactone. Under real conditions, the microstructure of the dough matrix significantly affected the metabolites production and cell activity.

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

ABSTRACTMixing 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.

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.

Factors Associated with Dough Stickiness as Sensed by Attenuated Total Reflectance Infrared Spectroscopy

ABSTRACTAttenuated total reflectance (ATR) and Fourier transform infrared (FTIR) spectroscopy have been applied in the characterization of sticky dough surfaces. The characterization provides insight in the chemical distribution of gluten protein, starch, water, and fat during dough kneading. ATR is especially useful for selective sampling of dough surfaces because the depth of penetration of radiation is quite shallow. For dough, it is calculated to be in the order of 0.5–4 μm in the mid‐infrared, ideal for measurements of stickiness effects, where only the dough surface is of interest. To investigate the cohesive and adhesive properties of the individual dough constituents, dough was peeled from the ATR plate to study the material that adhered to it. The infrared spectra obtained indicate that fat and gluten protein appear to be located at the outer sticky dough surfaces, rather than water and starch. In comparison with gluten, the fatty component showed relatively strong adhesive forces to the ATR plate; a high residual fraction was measured after peeling the dough. Gluten proteins display different cohesion and adhesion properties that are strongly dependent on their hydration state. This indicates that the degree of hydration of gluten proteins contributes to the sticky properties of (overkneaded) dough. When analyzing gluten protein in D2O instead of a dough matrix, more or less similar results were obtained. Significant differences in amide I and amide II intensities were measured for kneaded and stretched gluten protein in comparison to untreated, wet gluten. Besides changes in the vibrational properties of the amide groups, conformational changes in the tertiary protein structure also were observed. It appears that kneading and stretching of dough results in a major decrease in α‐helices content, accompanied by an increase of extended β‐sheet conformations.

Flavor Migration Out of Food Matrices: II. Quantifying Flavor Migration from Dough Undergoing Isothermal Heating

ABSTRACT A new approach using cold‐trap, on‐line sampling was applied to investigate migration rate of limonene, tert‐butylbenzene, and pyrazine in a flour dough matrix. Flavor equilibrium concentration and migration rates were shown to be strong functions of initial concentration. Due to encapsulation of flavor compounds at lower moisture content, it was not possible to totally extract the flavor compounds from the matrix by solvent extraction. The cold‐trap online sampling method could be satisfactorily used to generate data on flavor migration rates in dough matrices.

Lipid Extraction Process on Texturized Soy Flour and Wheat Gluten Protein‐Protein Interactions in a Dough Matrix

ABSTRACTProtein‐protein interactions between wheat flour and solvent‐extracted (SE) or nonsolvent extracted (NSE) texturized soy flours were compared. Doughs were prepared to contain varying ratios of texturized soy flour in combination with wheat flour. Sucrose esters (2.5%) were included in several formulations. Doughs were fractionated into soluble and insoluble fractions at pH 4.7 and pH 6.1. Fractions were dried, powdered, and analyzed using SDS‐PAGE and spectrophotometric techniques. Electrophoretic evaluation indicated interactions between wheat gluten proteins and texturized soy proteins in the absence of sucrose esters. Electrophoretic gels of the wheat‐soy flour mixtures maintained a characteristic soy protein band after acidification to the soy protein isoelectric point. Inclusion of sucrose esters increased the interaction. Texturization conferred effects similar to that of sucrose ester on both forms of lipid‐extracted soy. Sulfhydryl analyses using 7‐chloro‐4‐nitrobenzo‐2‐oxa‐4, 3‐diazole (NBD‐Cl) revealed no change in the relative amount of sulfhydryl groups present in doughs prepared from either the texturized soy flours or the doughs containing equal amounts of wheat starch. These data indicate that interactions between soy protein from texturized soy flours and wheat proteins are not covalent.

Effect of Gaseous Acetic Acid on Dough Rheological and Breadmaking Properties

ABSTRACTBreads baked from wheat flours (protein contents 14.1–16.5% at 14.0% mb) that were pretreated with 2–3 mL of gaseous acetic acid per kg of wheat flour, showed maximum bread height and specific volume (cm3/g). Flour‐water suspension and the crumb pH values were gradually decreased with increased amounts of acetic acid. Gas generation and dough expansion tests with bread dough showed that the addition of the same amount of acetic acid, which achieved maximum specific volume, also showed the highest rate of gas generation and dough expansion. However, increasing acetic acid decreased these values. Scanning electron microscope (Cryo‐SEM) observation showed that the bread dough made from the same acetic acid‐treated flour indicated continuum and no cracks in the dough matrix. Evaluation of mixograms showed the decrease of mixing stability with increased acetic acid levels. Viscosity and water binding capacity of flour‐water suspensions were sharply increased by the addition of acetic acid at pH 5.0–3.5.

Detection of Active Yeast Cells ( Saccharomyces cerevisiae ) in Frozen Dough Sections

A new method based on fluorescence microscopy was developed to detect active yeast cells in cryosections of wheat dough. The sections were stained with 4',6-diamidino-2-phenylindole (DAPI) and counterstained with Evans blue. The active yeast cells in the sections appeared brilliant yellow and were readily distinguished from the red dough matrix. The dead cells allowed penetration of the Evans blue through the cell membrane, which interfered with the DAPI staining and caused the dead cells to blend into the red environment. The number of active yeast cells in fermenting dough sections containing different proportions of living and dead yeast cells correlated well with the gas-forming capability of the yeast in the dough but not with the results of the conventional plate count method. The new method allows the study of yeast activity not only during the different stages of frozen dough processing but also during the fermentation of doughs.