Glycosidases and glycanases of wheat flour doughs

Wheat flour contains hydrolytic enzymes capable of reducing dramatically the viscosity of the aqueous solution obtained by high-speed centrifugation of dough. Indirect evidence suggests this reduction in viscosity is largely due to the hydrolysis of glycosidic linkages in the non-starch polysaccharides. Soluble proteins and starch contribute less to the viscosity of this dough liquor than do the flour gums. The glycanases in flour relatively rapidly hydrolyse the galactomannan, guaran and carboxymethylcellulose. Flour also contains a wide range of enzymes capable of hydrolysing nitrophenyl α- and β-glucosides, α- and β-galactosides, α- and β-mannosides, α-arabinoside, β-fucoside and β-xyloside. Both the glycanases and the glycosidases show pH optima within the range 4-6 which covers the range normally encountered in dough.     

Sourdough reduces sodium in wheat flour doughs

The reduction of sodium in breads is already an imposed reality, which makes the search for alternatives essential. As sodium chloride has an effect on dough rheology, affecting the production process, it is important to evaluate these properties. This study evaluated the use of dry sourdough for the reduction of sodium in wheat flour dough. Sodium chloride (0–2.5 g/100 g) and dry sourdough (0–10 g/100 g) were added to wheat flour according to a central composite rotatable design, and farinograph, extensograph and pasting parameters were evaluated. The results were analysed using the response surface methodology. The farinograph and extensograph properties were strongly affected by both variables and presented opposite behaviours for most parameters. For pasting properties, only maximum viscosity and breakdown were affected. Despite the antagonistic behaviour of the variables when analysed separately, suitable parameters were reached in intermediate ranges for the manufacture of bakery products with reduced sodium content.     

On the influence of added lipid phases on the rheological properties of wheat flour doughs

Summary The influence of added lecithin on the stress relaxation behaviour of wheat flour doughs was studied. It was found that the relaxation modulus (G) was dependent of the lipid phase as well as on the type of flour to which the lecithin was added. As expected, when lecithin was dispersed in distilled water, the lamellar liquid-crystalline phase was obtained. This phase had the greatest influence on G. However when lecithin was dispersed in tap water or 1.55 mM CaCl₂ a mixture of different lipid phases was obtained. The influence of these mixtures on G was much less compared with lecithin in distilled water. The flours were from different flour streams, from a winter wheat and a spring wheat. One flour stream from the break system and one flour stream from the reduction system were used. It was found that the greatest increase in G due to the addition of lecithin was obtained for the flour streams from the reduction system. Furthermore, G increased more for the spring wheat than for the winter wheat.

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Über die Wirkungen eines Zusatzes von Lipidphasen auf die rheologischen Eigenschaften von Weizenteigen

Zusammenfassung Der Einfluß eines Lezithinzusatzes auf das Relaxationsverhalten der Weizenmehlteige wurde untersucht. Der Relaxationsmodulus (G) war sowohl von der Lipidphase als auch von dem Typ des Mehls abhängig. Wenn das Lezithin im destillierten Wasser dispergiert wurde, entstand, wie erwartet, eine lamellare flüssigkristalline Phase. Wenn das Lezithin in Leitungswasser oder in 1.55 mmol CaCl₂ dispergiert wurde, ergab sich eine Mischung verschiedener Lipidphasen, deren Einfluß auf G viel geringer war als der des Lezithins im destillierten Wasser. Bei den Mehlen handelte es sich um verschiedene Passagenmehle aus Sommer- und Winterweizen, weiterhin um ein Schrotmehl und ein spezielles Mehl (Reduktionmehl). Die größte Steigerung des G-Modulus wurde bei Zugabe von Lezithin zu dem speziellen Mehl gefunden. Weiter erhöhte sich der Modulus stärker bei Sommerweizen als bei Winterweizen.

     

The effect of lipoxygenase action on the mechanical development of wheat flour doughs

The mechanical development of dough has been followed by measurement of the relaxation time of dough samples after mixing to various levels of work input. Parallel determinations of free and bound lipid have also been made. When doughs were mixed in air, addition of full-fat, enzyme-active soya bean flour (subsequently referred to as “soya flour”) resulted in an increase in relaxation time, particularly at higher work levels. The magnitude of this improvement increased with increasing work input and was dependent on the rate of work input. Addition of soya flour also enabled a higher level of mechanical work to be introduced before dough breakdown occurred. When doughs were mixed under nitrogen, or when the soya flour was heat denatured, no change in the rheological properties compared with the respective control doughs was found. The release of bound lipid, which occurred during dough development in air in the presence of soya flour, could also be induced by adding purified lipoxygenase to the dough, together with linoleic acid as a substrate. This resulted in rheological changes similar to those observed using soya flour. However addition of enzymically pre-peroxidised lipid to doughs mixed in nitrogen was without effect on relaxation times. These findings suggest that lipid release is linked with structural changes in dough protein and provide further support for a mechanism of coupled oxidation of protein -SH groups by lipoxygenase.     

Particle size,rheological and structural properties of whole wheat flour doughs as treated by high pressure

Effect of high-pressure treatment (300–600 MPa) and flour-to-water ratio (1:1, 1:2, 1:3, and 1:4) on functional, rheological, thermal, and structural properties of whole wheat flour dough were investigated. The particle size distribution, especially Dv90 (90% of the volume distribution), was significantly reduced by the pressure treatment. The damaged starch content increased significantly with the applied pressure and water content. The damaged starch absorbed more water, and subsequently increased the water holding capacity. Thermal transitions and mechanical property of pressure-treated samples were measured by differential scanning calorimetry, and rheometry, respectively. The peak viscosity, hot paste viscosity, and final viscosity decreased significantly with increasing pressure intensity. Hardness increased with the increasing pressure level while stickiness decreased at similar conditions. Fourier-transform infrared spectroscopy showed changes in the amide I region of the wheat protein. The sodium dodecyl sulfate polyacrylamide gel electrophoresis further indicated changes in the protein subunits that occurred after pressurization.     

A rheological investigation of the role of water in wheat flour doughs

Summary. Doughs of wheat flour, salt and water have been mixed to various levels of work input and water content. Rheological tests have shown that above a particular water content the dough system is unaffected by further addition of water. It is proposed that the water in dough is held with various degrees of strength and that the distribution of water is dependent upon the mechanical work input.     

Flour Quality effects on percolation of gas bubbles in wheat flour doughs

To investigate how flour affects crumb structures, we used Synchrotron X-ray tomography to scan and capture the growth of gas bubbles in leavened and unleavened bread doughs of two different flours. Bubbles were mobile in all doughs; they coalesced and disproportionated with the rate of coalescence being higher in leavened doughs. In unleavened dough, new bubbles were detected, attributed to arise from poro-visco-elastic relaxation of gluten as dough rested. In each yeasted dough, a single, massively inter-connected cluster formed which percolated at ~26% dough porosity irrespective of flour type in dough. Following percolation, dough expansion was driven primarily by growth of the percolating bubble. Between flours, the rate of coalescence was higher in Wylkatchem (Wylk), an Australian flour dough, than in Canadian Western Red Spring (CWRS) flour dough, known for superior proof and bake qualities. How the physical and rheological properties of dough liquors could have affected the stabilities of bubbles in these doughs have been discussed.     

Rheological properties of commercial chestnut flour doughs with different gums

Rheology of chestnut flour (CF) doughs with arabic gum (AG), carboxymethyl cellulose (CMC), guar gum (GG) and tragacanth gum (TG) at different concentrations (up to 2.0%) were determined at 30 °C using a controlled stress rheometer. The mixing characteristics at 30 °C were achieved using Mixolab^® apparatus. Shear (0.01–10 s^?1), oscillatory (1–100 rad s^?1 at 0.1% strain), creep‐recovery (50 Pa for 60 s) and temperature sweep (30–100 °C) tests were performed. Rheological properties were significantly modified by gum added. Apparent viscosity of CF doughs, storage and loss moduli increased at content of AG (above 0.5%), CMC (at 1.0%), GG (above 1.5%) and TG (at 1.0%). Flow curves and mechanical spectra were fitted using Cross model and power models, respectively. The gelatinisation temperatures increased with gums. The same pasting trend was noticed using Mixolab^®. Creep‐recovery data, fitted by Burgers model, showed that elasticity of CF doughs improved with GG.     

The microflora of the sour dough of wheat flour bread XII. Effect of freezing on the viability and functional properties in wheat flour doughs of microbial mass from lactic acid bacteria

Summary The effect of freezing (at –196 °C in 10% skimmed milk) and storage of the frozen microbial mass from lactic acid bacteria,Lactobacillus brevis, L. plantarum, L. cellobiosus andStreptococcus faecium, on viability and functional properties, in wheat flour doughs, have been studied. Freezing the biomass led to variable, but acceptable, survivals (34.3%–78.6%), depending on the species. Frozen and unfrozen biomass, when added to wheat doughs, produced similar values of pH and total titratable acidity during fermentation. Significant differences in acetic and lactic acid production were detected for some species. Frozen biomass fromL. brevis produced lessl(+)- andd(–)-lactic acid (43%) than the corresponding unfrozen material, whereas frozen biomass fromL. plantarum produced more acetic (61 %) and lactic acid (57%) than unfrozen. These differences were not reflected in bread characteristics (pH, total titratable acidity and flavour). Storage of frozen biomass for 30 days at –30 °C did not result in significant changes in the pH and or titratable acidity of the doughs nor in bread characteristics. At that time, acetic and lactic acid levels reached values close to these of the unfrozen biomass for all the microorganisms used.

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Die Mikroflora des Weizensauerteiges XII. Mitteilung: Wirkung von Tiefkühlung auf die Lebensfähigkeit und Funktionseigenschaften der Biomasse aus Milchsäurebakterien in Weizenteigen

Zusammenfassung Es wurde der Wirkung von Tiefkühlung (bei –196 °C in 10% Magermilch) und Lagerung von tiefgekühlter Biomasse aus Milchsäurebakterien,L. brevis, L. plantarum, L. cellobiosus undS. faecium, auf ihre Lebensfähigkeit und Funktionseigenschaften in Weizenteigen nachgegangen. Die Tiefkühlung der Biomasse verursachte veränderliche, jedoch akzeptable Überlebensraten (34,3%–78,6%) in Abhängigkeit von der Spezies. Beim Zusatz von tiefgekühlter Biomasse und nicht tiefgekühlter Biomasse zu Weizenteigen wurden ähnliche pH-Werte und Säuregrade während der Gärung erreicht. In manchen Spezies wurden bedeutsame Unterschiede in der Milchsäure-und Essigsäurebildung beobachtet. Die tiefgekühlte Biomasse vomL. brevis bildete wenigerl(+)-undd(–)-Milchsäure als die nichttiefgekühlte, während die tiefgekühlte vomL.plantarum mehr Milchsäure und Essigsäure als die nichttiefgekühlte bildete. Diese Unterschiede erschienen nicht in den Broteigenschaften (pH-Wert, Säuregrad, Geruch und Geschmack). Die Lagerung der tiefgekühlten Biomasse bei –30 °C während 30 Tagen verursachte keine bedeutsame Veränderung weder im pH-Wert und Säuregrad des Teiges noch in den Broteigenschaften. Essigsäure-und Milchsäuregehalte erreichten zugleich ähnliche Werte wie die nichttiefgekühlte Biomasse in allen Mikroorganismen.

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This paper is a part of a doctoral thesis for M. J. T.     

Reaction of sorbic acid in wheat flour doughs: reaction with thiols.

The general characteristics of the reaction between sorbic acid and thiols are reviewed. Cysteine adds to the conjugated diene in position 5 to form the substituted 3-hexenoic acid. This is labile in acid solution, yielding a quantitative amount of sorbic acid. When wheat flour doughs are treated with sorbic acid and heated, a significant amount of the sorbic acid is not recovered on extraction with methanol. The use of acidified methanol leads to a quantitative recovery of the preservation and evidence is presented to suggest that sorbic acid-thiol adducts are formed. This is the first report of 'reversibly bound' sorbic acid in a food.     

Rheological properties of wheat flour doughs I.—Method for determining the large deformation and rupture properties in simple tension

A method and an apparatus are described for determining the large deformation and rupture properties of wheat flour doughs in simple tension. Dough rings are submerged in a liquid of matching density to prevent the dough from deforming under its own weight and are stretched at constant rates of extension until rupture occurs. Stress-strain curves obtained at different temperatures and extension rates on doughs prepared from a medium strength flour and a weak flour are presented, and the effects of rest period, mixing time, and mixing atmosphere on dough properties are discussed.     

The bubble size distribution and its evolution in non-yeasted wheat flour doughs investigated by synchrotron X-ray microtomography

Determination of the bubble size distribution at the end of mixing and controlling its changes are the basis for improving bread quality before it is fully manufactured. X-rays from a synchrotron source (Biomedical Imaging and Therapy beamline, Canadian Light Source) were used to rapidly characterize the bubble size distribution and its evolution in non-yeasted dough subsamples as a function of time for 3 h following mixing. A complete X-ray microtomography scan was completed within 120 s. The higher number density of bubbles in dough compared to results previously reported in the literature was attributed to the better contrast and higher resolution (smaller pixel size, 8.75 μm) of the reconstructed X-ray images generated from synchrotron X-rays. The bubble size distribution was very well characterized with a lognormal distribution function. This distribution had a median bubble radius of 22.1 ± 0.7 μm at 36 min after the end of mixing which increased to 27.3 ± 0.7 μm over 162 min, a trend indicative of transport of gas in the dough due to disproportionation. This is the first time disproportionation in non-yeasted wheat flour doughs has been monitored directly under bulk conditions relevant to dough in bakery conditions. These results show that the diffusion-driven dynamics of bubbles in non-yeasted bread doughs can be followed by X-rays from a synchrotron source via feature extraction using image analysis software.     

Comparative properties of cakes prepared from rice flour and wheat flour

Received: 20 September 1999     

蕨麻对面包制品品质特性的影响

主要研究面粉中添加1％～9％的蕨麻粉对面团粉质特性以及面包品质的影响。结果表明．随着蕨麻粉添加量的增加,面团的吸水率逐渐增高,面团的形成时间和稳定时间延长,弱化度降低;随着蕨麻粉添加比例的增加,面包硬度增加,面包的感官评分总体上呈现降低趋势,但是当蕨麻添加量大于5％时,面包体积急剧减少,面包纹理结构变差,质地和口感都明显下降,因此,蕨麻粉在面包粉中的合理添加比例为5％。     

出粉率对小麦粉理化特性及面条品质的影响

从制粉生产线上取82种系统粉,并根据灰分含量和流量配制出粉率为55％、60％、65％、70％、75％、80％、88％、95％、100％等9种不同小麦粉.对不同出粉率小麦粉理化特性及面条品质进行研究,结果表明:出粉率为55％～70％时,小麦粉来源于胚乳,小麦粉理化特性及面条品质较好,且各类指标在较小范围内浮动;出粉率为7...     

Fundamental rheological and textural properties of doughs and breads produced from milled pearled barley flour

Barley has long been known as a good source of fibre and in particular beta-glucan, but increased consumer awareness has meant that this is only now being exploited by food scientists and the food industry. In this study, doughs and breads were produced using pearled barley flour (PBF) in different ratios (30, 50, 70 and 100%) to wheat flour. A 100% wheat flour formulation was used as a control. The flour formulations were evaluated for protein content; the dough rheological properties of the formulations were evaluated using fundamental oscillatory tests and uniaxial extension tests. The baked breads were evaluated for volume, texture, moisture, dietary fibre and beta-glucan. Digital image analysis of the crumb grain was also carried out. Protein analysis revealed that increasing the amount of PBF in the formulation leads to a significant (p < 0.001) decrease in the protein content of the formulation. Starch pasting properties were also affected by an increase in PBF concentration, with an increase in PBF significantly increasing the peak viscosity, breakdown, setback and final viscosity of the starch slurries of the formulations. Extensional rheology revealed that increasing the PBF in the doughs leads to the doughs rupturing at lower extensions and with a lower force. Bread volume between treatments was found to be significantly (p ≤ 0.001) different, with an increase in PBF inclusion leading to smaller loaves. Texture profile analysis of the bread slices showed that breads containing higher ratios of PBF had a significantly harder (p ≤ 0.001) and less cohesive (p ≤ 0.001) crumb. Low levels of PBF (≤50%) did not significantly effect loaf volume or crumb texture, however, and the total dietary fibre and beta-glucan levels of the loaves were significantly increased (p ≤ 0.001) with increasing levels of PBF in the formulation, even at low levels of inclusion.     

面粉安全与面粉增白剂

我国自古重视农业生产,尤其是进入现代,杂交水稻等一系列富含高新技术的农产品问世,使得我国用世界1/7的土地,养活了世界上1/3的人口,并且一跃成为世界五大产粮大国之一.这些都是我们值得欣喜和骄傲的成绩.然而,在这些成绩的背后,我们同样要清醒的看到,现阶段的主要任务已远不止满足广大人民的粮食需求,而是要更进一步,关注粮食等食品的安全问题.我国目前正在法制化道路上不断前行,与粮食安全相关的各项法律法规还在逐渐地建立健全.