小麦粉面团形成过程水分状态及其比例变化

为研究醒面对冷冻面团品质的影响,本文研究了醒面过程中（0、30、60、90、120 min）,面团水分分布的变化规律以及面团冷冻后冰晶分布、微观结构和蠕变恢复特性的变化。结果表明：随着醒面时间的延长,面团中可冻结水含量降低了0.96%;微观结构的结果表明,面团在冻结过程中形成的冰晶空隙和数量逐渐减小,冰晶分布越来越均匀;随着醒面时间从0 min延长至120 min,冷冻面团的平均空隙面积从22.65减小到11.80,空隙数目从10627.00减少到3346.00;随着醒面时间的延长,在蠕变阶段,冷冻面团的最大蠕变柔量J_max显著增加（P<0.05）,零剪切粘度η₀显著降低（P<0.05）;面团醒发120 min后,冷冻面团最大蠕变柔量J_max降低了0.50×10⁻⁴ Pa⁻¹,零剪切粘度η₀降低了0.43×10⁵ Pa⁻¹,这说明冷冻面团的硬度降低,面团的形状更容易保持;在恢复阶段,瞬时柔量J₀与黏弹性柔量J_m分别增加了1.26×10⁻⁴和2.88×10⁻⁴ Pa⁻¹,冷冻面团的恢复力增加。综上,醒面降低了面团中可冻结水的含量,提高了面团的持水力,减小了冷冻过程中冰晶对面团网络结构的破坏,从而提高了冷冻面团的品质。

     

Changes in flour lipids during the storage of wheat flour

High- and low-grade spring and winter wheat flours of ～13% moisture were stored at 15, 25 and 37 °C and the lipids were then extracted with water-saturated n-butanol. In the original (control) flours there were more neutral lipids and glycolipids in low-grade winter than in high-grade winter and in low-grade spring than in high-grade spring flours, but there were no corresponding differences in the amounts of phospholipids. The total extractable lipid contents of the flours remained constant in the samples stored at 15 °C, but there were slight losses in the samples stored at 25 and 37 °C. Total lipid contents determined by acid hydrolysis remained constant in all cases indicating that no loss of fatty acids had occurred on storage. There was sufficient hydrolysis of all glycerides to account for the increased amounts of free fatty acids in the stored flours. Some complete deacylation of lipids to free fatty acids and water-soluble products was indicated. The fatty acid composition of all lipids remained constant, and there was no evidence of any lipoxygenase or other enzymic degradation of fatty acids. Stereoanalysis of the principal glycerides indicated that phosphatidylcholine (and probably also phosphatidylethanolamine) was specifically hydrolysed at the 2-position, presumably by phospholipase-A₂. Hydrolysis of triglycerides, diglycerides and monoglycerides was attributed to the action of wheat and microbial lipases of unknown specificity. Stereoanalysis of N-acylphosphatidylethanolamine and the galactosyldiglycerides was not attempted, but it was deduced that they were randomly hydrolysed at the 1- and 2-positions. The changes found in the flour lipids differed from those reported to occur in germinating wheat and in stored damp wheat flour which had been damaged by moulds.     

Rheological properties of yeasted and nonyeasted wheat doughs developed under different mixing conditions

BACKGROUND: In order to explore the differences in rheological behaviour of full formula and flour/water doughs due to mixing, small‐amplitude oscillatory strain (SAOS) rheological measurements were made on fully developed nonyeasted and inactivated yeasted dough formulations mixed at various speeds using the Brabender Farinograph and the Bohlin ReoMixer. These results were compared with large‐strain empirical rheological results (including Kieffer rig uniaxial extension) as well as baking test results to determine differences due to mixer speed and/or flow distribution. RESULTS: The uniaxial extension and baking tests detected mixing speeds with incomplete dough development. Above those speeds, energy input to peak development was relatively constant in the Farinograph. Extensibility trends showed increases with speed in the yeasted dough samples, which were attributed to variation in fermentation time during mixing to peak torque at different speeds. While SAOS results did not show differences due to mixing speed, they did detect differences between the yeasted and nonyeasted dough formulations, as well as significant differences (P < 0.01) between yeasted doughs mixed in the two different mixers. CONCLUSION: The results indicate that known differences in the distribution of elongational and shear flows in the two mixers impact the development of dough structure during mixing. Copyright © 2008 Society of Chemical Industry     

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.     

The formation and properties of wheat flour doughs

Among the cereal flours, only wheat flour will form a viscoelastic dough when mixed with water. The viscoelasticity appears to be because the gluten proteins are water compatible and thus will swell and interact. The gluten protein's large molecular size and low charge density appear to allow them to interact by both hydrogen and hydrophobic bonds. Wheat flour doughs are also unique in their ability to retain gas. This property appears to result from a slow rate of gas diffusion in the dough. The third major unique property of wheat flour doughs is their ability to set in the oven during baking, and thereby to produce a rigid loaf of bread. Although not clearly understood, this appears to be a heat-induced crosslinking of the gluten proteins.     

Controlled production of acetic acid in wheat sour doughs

Summary Sour doughs are characterized by their pH value, their total amount of titratable acidity (TTA) and their fermentation quotient (FQ=mol ratio lactic acid/acetic acid). At comparable TTA, the FQ may evidently affect the sensory properties and the shelf life of breads. Therefore, attention should be directed to controlling FQ by enhancing or suppressing the production of acetic acid. Over a limited range, this is possible by setting to appropriate levels the process parameters temperature and dough yield. Alteration the availability of the hydrogen acceptor (via fructose or invert sugar supply) is another way of influencing the FQ directly by shifting the heterolactic pathway from the ethanol to the acetate branch and vice versa. The objective of this investigation was to combine the effects of dough yield and temperature with those of fructose supply in order to improve the control of FQ. The central composite design was used to arrange the experiments to quantify the effects of temperature (25–40° C), dough yield (180–320) and fructose supply (0–10 g/100 g flour) on fermentations of sour dough started withLactobacillus brevis 25 a. In this way, it was possible to modulate the FQ levels between 0.9 and 4.5. The results indicate, that temperature has no significant effect, and that fructose is more efficient in influencing the FQ than dough yield. No interactive effects were detected.

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Kontrollierte Essigsäurebildung in Weizensauerteigen

Zusammenfassung Sauerteige werden durch ihren pH-Wert, ihren Gesamtgehalt an titrierbaren Säuren (TTA) und ihren Gärungsquotienten (FQ=molares Verhältnis Milchsäure/Essigsäure) charakterisiert. Bei vergleichbaren Säuregehalten kann sich der Gärungsquotient auf die sensorischen Eigenschaften und die Haltbarkeit der Brote auswirken. Deshalb sollte er über die Förderung oder Hemmung der Essigsäurebildung kontrolliert werden. Das läßt sich über einen begrenzten Bereich durch geeignete Einstellungen der Prozeßparameter Temperatur und Teigausbeute bei der Sauerteiggärung erreichen. Ein anderer Weg bietet sich über eine gezielte Einflußnahme auf die Verfügbarkeit organischer Wasserstoffacceptoren (über das Angebot von Fructose oder Invertzucker) an, um den Gärungsquotienten direkt durch Umlenken der heterofermentativen Stoffwechselwege von der Ethanolzur Essigsäurebildung (und umgekehrt) zu veranlassen. Das Ziel der vorliegenden Arbeit war es daher, die von der Temperatur und der Teigausbeute ausgehenden Ein flüsse mit denen eines Fructoseangebotes zu kombinieren, um eine effizientere Kontrolle des Gärungsquotienten zu erarbeiten. Zu diesem Zweck wurden Mehrfaktorversuche auf der Basis des Central Composite Designs angesetzt, um die Effekte der Temperatur (25–40 °C), der Teigausbeute (180–320) und des Fructoseangebotes (0–10 g/100 g Mehl) auf Sauerteiggärungen mitLactobacillus brevis 25 a zu quantifizieren. Auf diesem Wege konnte der Gärungsquotient über einen Bereich von 0,9 bis 4,5 kontrolliert variiert werden. Die Ergebnisse zeigten, daß dabei von der Temperatur kein signifikanter Einfluß ausging und daß Fructose effizienter zur Einstellung des Gärungsquotienten genutzt werden kann als die Teigausbeute. Interaktive Effekte wurden nicht nachgewiesen.

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Publication No. 6157 of the Federal Center for Cereal, Potato and Lipid Research in Detmold and Münster     

Chemical changes in nitrogenous compounds during fermentation of sour doughs and bread doughs

Summary The evolution of sour doughs (SD), prepared using a wheat bran extract as the starting material, and their respective bread doughs (BD) has been investigated by determining the chemical changes which take place in 0.85 mol/L NaCl-soluble nitrogen compounds during fermentation. The quantitative changes determined are: total nitrogen content (TN), primary amine nitrogen (AN) and-amine nitrogen of free amino acids (AAN) in the total soluble fraction (SN), protein (PSN) and non-protein (NPSN) subfractions. During fermentation,-amine nitrogen of the free amino acids (AAN_SN) and peptides (AN_NPSN-AAN_SN), increase in SD and decrease in BD. Changes are larger and faster in peptide nitrogen and even larger during the third and fifth steps. The total protein content (TN_PSN) decreases in both SD and BD. Results are discussed in relation to the quality of the bread obtained in each case.

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Chemische Veranderungen der Stickstoffverbindungen aus Sauerteigen und den damit hergestellten Brotteigen

Zusammenfassung Es wird die Entwicklung von Sauerteigen mit Weizenkleiextrakt als Starter und ihren entsprechenden Brotteigen durch Bestimmung der chemischen Veranderungen der in 0,85 mol/L NaCl1 slichen Stickstoffverbindungen wahrend der Gärung untersucht. Die quantitativen Veränderungen des Gesamt-Stickstoffgehalts (TN), des primären Aminostickstoffs (AN) und des -Aminostickstoffs der freien Aminosauren (AAN) in der loslichen Fraktion (SN) und in den Proteinen (PSN) und Nicht-Proteinen (NPNS) der Subfraktionen. Wahrend der Gärung steigt der Anteil des-Aminostickstoffs in den freien Aminosäuren (AAN_SN) und Peptiden (AN_NPSN-AAN_SN) in den Sauerteigen (SD) an und vermindert sich in den Brotteigen (BD). Die Veränderungen sind hoher und schneller beim Peptidstickstoff und größer wahrend der dritten und funften Stufe sowohl beim Sauer- als auch beim Brotteig; in beiden nimmt der Proteingehalt (TN_PSN) ab. Die Ergebnisse werden bezogen auf die Qualität der hergestellten Brote besprochen.

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Paper presented at the 7th World Congress of Food Science and Technology, Singapore (Singapore), 28 September – 2 October 1987     

Effect of soybean proteins on gluten depolymerization during mixing and resting

BACKGROUND: Gluten and soy proteins interact as a consequence of dough mixing; however, there is no evidence of the effect of soy protein on gluten depolymerization. The aim of this study was to assess the depolymerizing effect of soy protein on gluten network after mixing and resting of mixed doughs. Therefore, the changes in glutenin macropolymer (GMP) content, protein composition and free sulfhydryl content were evaluated. RESULTS: The protein profile from gluten–soybean blends, obtained by multistacking SDS‐PAGE, showed differences when compared to gluten profile. Soy and gluten proteins were extracted together with SDS buffer, which showed that soy proteins remained associated to insoluble wheat proteins even after hand‐washing the dough to obtain gluten. GMP content was determined to analyze the effect of soy protein on GMP gel formation. Protein content of GMP obtained from flour mixes and doughs was increased by inactive soy flour because soy proteins became insoluble and precipitated together with GMP. Active soy flour decreased GMP content due to gluten depolymerization. CONCLUSION: Soy proteins were associated to wheat protein through physical interaction and covalent and non‐covalent bonds during mixing and resting. These interactions produced large and medium‐size polymers. This fact increased SDS solubility of insoluble gluten proteins, producing a weakening of the gluten network. Physicochemical status of soy protein in the product had a great influence on how wheat–soy proteins interact. Copyright © 2007 Society of Chemical Industry     

Importance of wheat lipoxidase in the oxidation of free fatty acids in flour-water systems

Wheat flour was extracted with water, and the aqueous extract and flour residue were used in mixing experiments. The enzyme system (βoxidation?) responsible for the pro rata oxidation of free fatty acids (FFA) was present only in the flour residue, and lipoxidase was present only in the aqueous extract. It was calculated that lipoxidase could account for only a small proportion of the oxygen consumed in oxidations of FFA, and the significance of wheat flour lipoxidase in dough rheology is therefore less than has been hitherto assumed.     

Small and large deformation rheology for hard wheat flour dough as influenced by mixing and resting

ABSTRACT:  The effects of mixing and resting on the physicochemical properties of doughs prepared with strong and weak hard wheat flours were investigated, specifically concerning aspects related to their rheological behavior and molecular mobility. Small deformation dynamic tests showed that, during the initial resting period, the complex modulus G * decreased and phase angle decreased for undermixed dough, whereas overmixed dough showed opposite trends. G * values for optimally mixed dough did not vary during the resting period investigated. This was more obvious for the strong dough. Large deformation tests more clearly showed differences among optimal, under-, and overmixed dough, and also between doughs prepared with strong and weak flour. Optimally mixed dough exhibited the highest peak stress and strain for both samples. In addition, the peak stress of dough prepared with the strong flour was higher than that of dough prepared with weak flour. Inconsistent results between small and large deformation tests implied that small and large deformation tests reflected different structural aspects of dough. NMR measurements were performed to estimate the relaxation properties of the sample upon resting. Decreased water mobility during resting, indicated by decreasing T ₁ relaxation time, was possibly attributed to increasing molecular interactions caused by continued hydration. Evidence of additional molecular interactions created by mixing was also observed.     

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.     

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％。     

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.     

Changes in intramuscular lipids during ripening of Iberian dry-cured ham

Thirty-one thighs were obtained from Iberian pigs fattened with acorns and were processed during 22 months in the traditional dry-curing process. Lipolysis affecting intramuscular fat during the processing of Iberian dry-cured ham has been analyzed by studying the changes of glycerides, phospholipids and free fatty acids in lipids from Biceps femoris muscle. Little change affected the fatty acid composition of glycerides during processing. A double-phased increase in the acidity values and a decrease in the quantity of fatty acids of phospholipids during the processing were observed. There seems to be a relationship between the extension of the lipolysis taking place during the maturing and the processing conditions and raw material used.     

小麦脂类研究进展

脂类物质是小麦面粉中的重要功能性成分,它对面团特性、面包以及馒头的品质影响很大.综述了小麦脂类的研究进展,包括小麦脂类的分布与种类,脂类的提取方法,脂与淀粉的相互作用以及对淀粉特性的影响,脂与蛋白质的相互作用,脂在食品中的作用机制,为以后的研究提供了可靠的参考.     

Biochemical evolution of nitrogen compounds during fermentation of wheat bread doughs containing pure cultures of lactic acid bacteria

Summary The metabolic activities of three species of lactic acid bacteria (Lactobacillus brevis, L. plantarum andStreptococcus faecium) during wheat bread dough fermentation have been investigated by evaluating the biochemical changes which occur in 0.85 mol/L NaCl-soluble nitrogen components in unfermented, 4-h and 24-h fermented straight doughs. Non-protein nitrogen compounds increase during a 24-h-fermentation period in all doughs. Exoproteolytic activity is denoted mainly inL. plantarum fermented doughs by an important rise in the free amino acids. Doughs containingL. brevis show a larger production of peptides over a 24-h fermentation period and strong nutritional requirements on low-molecular-weight peptides are evidenced byStreptococcus faecium over short fermentation periods. Progressive depletion in the polypeptides and protein contents as well as a decrease in the estimated protein chain length over the fermentation period forL. plantarum andSt. faecium containing doughs are evidence of endoproteolytic activities in the high-molecular-weight soluble components. An increase in the size of the protein fragments released in the 4-h fermented doughs containingL. brevis denotes enzymatic hydrolysis on non-soluble protein chains.

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Biochemische Veränderungen an Stickstoffverbindungen während der Gärung von Weizenteigen mit reinen Kulturen von Milchsäurebakterien

Zusammenfassung Es wurde die Stoffwechselaktivität von 3 Milchsäurebakterien,L. brems, L. plantarum undSt. faecium, während der Gärung von Weizenteigen durch Bestimmung der biochemischen Veränderungen in 0,85 mol/L NaCl-löslichen Stickstoffverbindungen von nicht fermentierten, 4 h und 24 h fermentierten direkt geführten Teigen untersucht. Der Gehalt an Nicht-Protein-Stickstoffverbindungen stieg in allen Teigen während der 24-h-Gärung an. Es wurde exoproteolytische Aktivität festgestellt, besonders in den mitL. plantarum fermentierten Teigen, durch einen erheblichen Anstieg der freien Aminosäuren. Teige, dieL. brevis enthielten, wiesen die größere Peptonbildung bei der 24-h-Gärung auf; es wurden stärkere Nahrungsansprüche an Peptiden mit niedrigem Molekulargewicht beiSt. faecium in kurzen Gärungszeiten beobachtet. Progressiver Abfall des Polypeptid-und Proteingehaltes sowie Abnahme der Protein-Kettenlänge während der Gärung bei den Teigen, dieL. plantarum undSt. faecium enthielten, weisen auf endoproteolytische Aktivität auf lösliche Verbindungen mit hohem Molekulargewicht hin. Eine Zunahme der Größe der Proteinfragmente bei den 4-h-fermentierten Teigen mitL. brevis zeigt eine enzymatische Hydrolyse der nicht löslichen Proteinkette an.