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.     

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     

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.     

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％。     

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.

     

Changes in peroxidase isoenzyme patterns of wheat during ripening and storage

Summary Polyacrylamide-gel disc electrophoresis of water soluble peroxidase was carried out with wheat kernels taken at intervals during ripening and storage of the kernels. The mobility of anodic isoenzymes gradually decreased during ripening and disappeared from the pattern of the ripe wheat. After harvest and during storage only cathodic isoenzymes could be detected that had not been found in the ripening kernels. Isoenzymes of pI 7.9 (remaining at the start) were present throughout the whole period of investigation.

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Änderung der Verteilung von Peroxidase-Isoenzymen während der Reifung und Lagerung von Weizen

Zusammenfassung Die wasserlöslichen Peroxidasen von Weizen wurden während der Reifung und Lagerung der Körner durch Polyacrylamidgel-Elektrophorese studiert. Die Beweglichkeit der anodisch wandernden Isoenzyme nahm während der Reifung ab und diese verschwanden aus dem Wasserextrakt des reifen Weizens. Nach der Ernte und während der Lagerung konnten nur kathodisch wandernde Isoenzyme nachgewiesen werden. Nicht wandernde Peroxidase (pl 7,9) war in der Startzone während der ganzen Versuchsperiode zugegen.

     

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.     

Texture properties of formulated wheat doughs Relationships with dough and bread technological quality

Texture properties of wheat doughs were determined with a texturometer by using texture profile analysis (TPA) as well as Chen and Hoseney methodologies. The time elapsed between two compressions and strain were optimized so that meaningful values were obtained for TPA. Single effects and interactions between flour type, the breadmaking process and anti-staling additives (i.?e. monoglycerides, diacetyl tartaric ester of monoglycerides, sodium stearoyl lactylate, carboxymethylcellulose and hydroxypropylmethylcellulose) on dough texture properties (i.?e. springiness, resilience, hardness, cohesiveness, adhesiveness, chewiness, gumminess and stickiness) were estimated. The breadmaking process and addition of hydrocolloids had the most important effects and interactions on TPA. Hydrocolloids and α-amylase increased dough stickiness. Dough cohesiveness was a good predictive parameter of bread quality. Water content, acidity values and gluten quality were the main factors determining the texture properties of dough.     

小麦储存中生理活性与加工品质的变化

研究以15个小麦品种为材料,研究小麦在不同储藏温度下的籽粒特性和食用品质的变化。结果表明:储存过程中小麦的品质特性的变化受到温度和样品自身因素的影响。40℃条件下品质变化较快,尤其是种子生命活力,在储存3~6个月时已基本丧失了生命活力。储存过程中不同品种的小麦生命活力和食品加工品质的变化有很大的差异,说明小麦品种的耐储性可能存在可遗传的变异。籽粒硬度与损伤淀粉含量关系密切,但是小麦储存过程中硬度的变化尚无法得到确切的结论。     

Significance of viscosity profile of pasted and gelled formulated wheat doughs on bread staling

Pasting profile during cooking and cooling of straight/soured started bread doughs formulated with non fat-sodium carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), fungal α-amylase and fat-monoglycerides (MGL), diacetyl tartaric acid ester of mono-diglycerides and sodium stearoyl lactylate (SSL)-additives was recorded in the Brabender (BVA) visco-amylograph and Newport rapid viscoanalyser (RVA). Rheological results were correlated with bread staling kinetics during storage. Bread dough viscosity characteristics, derived from the RVA pasting profile during cooking and cooling, highly correlate with bread staling kinetic parameters. This is particularly so in the cases of peak viscosity, pasting temperature, and setback during cooling that can be considered as valuable predictors, at a dough level, of bread firming behaviour during storage. Individual and/or binary addition of surfactants to bread dough, particularly MGL and SSL, positively influence the level of the pasting parameters associated with a significant delay in bread firming. Individual additions of methylcellulose derivatives, mainly CMC, induce in general a deleterious effect on dough viscosity. Moreover, the simultaneous presence of CMC and HPMC results in a significant improvement of dough rheology during cooling. Binary mixtures SSL/CMC and MGL/CMC are not recommended from the viscoelastic point of view, due to antagonistic effects of the pair gum/surfactant that nullify the benefits of individual emulsifiers.     

A study of gluten extractability from doughs made from fresh and stored wheat flours

In contrast to the increase in protein extractability which normally occurs in making a dough from a flour, on overmixing dough from a freshly milled flour of good bread-baking quality, a progressive reduction occurs in the amount of acetic acid soluble proteins whereas the protein solubility shows little change in equivalent doughs made from similar flours stored for several years. Addition of artificially aged flour lipid, addition of oleic acid or defatting all tend to make the fresh flour imitate the behaviour of stored flour. Addition of diacetyl tartaric acid ester of mixed monoglyceride (which improves baking properties) to a stored flour makes the protein extractability move towards that of a fresh flour. It is suggested that in making dough from a fresh flour, there is a progressive binding of fresh flour lipid by the high molecular weight flour protein, which subsequently causes insolubility of this protein and that this binding like other lipid-protein interactions is a major factor influencing flour baking performance.     

Oxidation of free and esterified linoleic and linolenic acids in bread doughs by wheat and soya lipoxygenases

Lipids containing ¹⁴C-labelled linoleic and linolenic acids were added to flour which was then made into bread doughs with or without 2% enzyme-active soya flour. The ¹⁴C-labelled lipids and their oxidation products were analysed as intact lipids or as ¹⁴C fatty acid methyl esters by thin-layer chromatography. In the control doughs wheat lipoxygenase oxidised free fatty acids and monoglycerides. In doughs containing soya flour, steryl esters, triglycerides, diglycerides, mono-galactosyl diglycerides, digalactosyl diglycerides and phosphatidyl choline were also oxidised, and the oxidation of these lipids is attributed to soya lipoxygenase.     

Mixing properties of fibre-enriched wheat bread doughs: A response surface methodology study

Fibre-enriched baked goods have increasingly become a convenient carrier for dietary fibre. However, the detrimental effect of fibres on dough rheology and bread quality continuously encourages food technologists to look for new fibres. The effect of several fibres (Fibruline, Fibrex, Exafine and Swelite) from different sources (chicory roots, sugar beet and pea) on dough mixing properties when added singly or in combination has been investigated by applying a response surface methodology to a Draper-Lin small composite design of fibre-enriched wheat dough samples. Major effects were induced on water absorption by Fibrex that led to a significant increase of this parameter, accompanied by a softening effect on the dough, more noticeable when an excess of mixing was applied. Conversely, Exafine increased water absorption without affecting the consistency and stability of dough, which even improved when combined with Swelite. Fibruline showed little effect on dough mixing parameters, but showed synergistic effects with pea fibres. The overall result indicates that the use of an optimised combination of fibres in the formulation of fibre-enriched dough allow improving dough functionality during processing.