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.

     

Biscuit making properties of flours from hard and soft milling single variety wheats

Bench scale baking tests for two types of biscuits,¹ a hard sweet (HS) and a short sweet (SS), have been used to examine the biscuit making properties of a large number of flour samples from wheats grown in four consecutive years (1980–1983). Multiple regression models for prediction of biscuit properties using a range of standard cereal laboratory tests as independent variables on results from 1980–1981 harvest wheats confirmed earlier observations that such tests are of limited commercial value for biscuit flour specification. However the results of baking tests, with both types of biscuit, from single wheat varieties grown during 1981–1983 showed that flours from soft milling wheats (SMW) required less water to give biscuit doughs of standard consistency (measured instrumentally) than did flours from hard milling wheats (HMW). In addition biscuit doughs made with SMW flours gave greater oven spring, i.e. biscuits of lower bulk density, than doughs made from HMW flours. In each season the difference in the mean values of both parameters for flours milled from SMW and HMW was highly significant (P<0.001). With one exception the variability of the measured parameters within seasons was not significantly different between SMW and HMW. However within both SMW and HMW varieties highly significant differences (P<0.001) were observed between seasons for the mean values of both measured biscuit parameters. The effect of flour particle size on the biscuits was studied by regrinding a number of flours. With flours from both SMW and HMW reduction in particle size resulted in HS biscuits of higher density but SS biscuits of lower density.     

Carbohydrate Digestibility and Resistant Starch of Steamed Bread

Sixteen Australian hard and soft wheats and two U.S. hard wheats were milled into flours (break and reduction) for preparation of steamed breads. Chemical composition and rheological properties of the flour were determined. Steamed breads were analyzed for carbohydrate digestibility and resistant starch. There was no relationship between flour type, protein content and specific volume of steamed breads. Carbohydrate digestibility of steamed breads from soft wheat flour was higher than that of breads from hard wheat flour. Reduction flours produced steamed breads with higher carbohydrate digestibility than break flours. Resistant starch was higher in steamed breads from soft wheat flours than in those from hard wheat flours. Reduction flour produced higher resistant starch levels than break flours. Commercial white bread had resistant starch levels similar to those of steamed breads from soft wheat flour and hard wheat reduction flour.     

Differences in content and composition of free lipids and carotenoids in flour of spring and winter wheat cultivated in Poland

The work presents the content and composition of free lipids and carotenoids in spring and winter classes of wheat flour. It discusses genetical and physiological aspects of their synthesis and accumulation in wheat kernels and also indicates how methodological differences explain differences in results presented in the literature. It has been reported that spring wheat flours are richer in free lipids, especially in the non-polar fraction. The content of glycolipids ranged from 134 to 215 mg/100 g flour and was more stable within the winter wheat class. The percentages of the two main fractions, namely DGDG and MGDG, were similar in both wheat classes and reached ca. 77%. Phospholipids constituted the smallest fraction of the flour free lipids in both wheat classes; however, spring wheat flours were richer in these compounds, which is likely associated with a greater content of spherosomes in the endosperm of this wheat class. The free lipids of spring wheat flour contained more oleic and slightly less linoleic and linolenic acids. Spring wheat flour was also richer in carotenoids, although there were varieties in both classes that deviated from this. The main carotenoid was lutein, whose total percentage in the form of different isomers ranged from 71.3% to 83.3% and was slightly lower for spring wheat flour. Lutein, in the form of a trans-isomer, constituted about 62% and 70% of all carotenoids in spring and winter wheat flours, respectively.     

Origin and practical significance of the sticky dough factor in 1BL/1RS wheats

When translocated into wheat, the short arm of the 1R chromosome of rye carries with it linked resistance genes to powdery mildew, stripe rust, leaf rust and stem rust. The translocation is also reported to increase yield potential of hard wheats. However, many doughs made from some 1BL/1RS hard wheats are unacceptable for breadmaking purposes because of excessive stickiness and mixing intolerance. 1BL/1RS wheats may be sticky because of: the inheritance of secalin proteins from rye and absence of key glutenin subunits; higher amounts and/or differences in the composition of cell wall polysaccharides, β‐glucans and pentosans; and/or the presence of a ferulic acid ester moiety residing with the water‐soluble fraction of 1BL/1RS flours. None of these hypotheses has been proven or disproven, to date, as a cause of excessive stickiness. Investigators have found that 1BL/1RS doughs are not uniformly sticky and are in some instances less sticky than non‐1BL/1RS doughs. Significant genotype–environment interactions have been reported for dough stickiness and flour quality characteristics of 1BL/1RS wheats. Investigators have generally failed to find significant differences in the breadmaking performance of 1BL/1RS and non‐1BL/1RS hard wheats despite a report that 1BL/1RS doughs break down and soften during high‐speed mixing. The 1BL/1RS translocation has been shown to reduce cookie spread of soft wheat flours but has no deleterious effects on cake volume or texture. © 2002 Society of Chemical Industry     

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.     

The lipids of wheat III.—Further studies of the lipids of flours from single wheat varieties of widely varying baking quality

The work on flour lipids reported in Part II* of the series is extended to the lipids of wheats harvested in 1960-1962 inclusive. The same lipid components were found in each of the varieties studied although English flours contained much larger amounts of unesterified sterols than U.S. varieties of the same crop year. Quantitative lipid analyses demonstrated substantial varietal, seasonal, regional and environmental differences in lipid content and composition of the samples, but tentative correlations previously reported between lipid data and baking performance of the 1960 crop flours were not sustained by 1961 and 1962 crop results. Evidence is presented suggesting that only in very special circumstances would the performance of a flour be limited by the level of unsaturated fat available for the lipoxidase/thiol oxidation mechanism. Application of three quantitative TLC methods to flour lipids is described.     

Water Content, Water Soluble Fraction, and Mixing Affect Fundamental Rheological Properties of Wheat Flour Doughs

Fundamental rheological behavior of wheat flour doughs were compared with empirical results from a farinograph. Water contents of 42-47% and mixing times of 8, 16, and 24 min were examined. The storage modulus, G′, decreased when water content was increased from 42 to 45%. Dough produced from water extracted flours had high G′ and low δ. Increasing water content or mixing time decreased G′. There was a linear relationship (slope = 0.30) between G′ and the farinogram peak height for the reconstituted (water-soluble fraction added back), flour-water, and freeze-dried flour-water doughs. The extracted flour doughs also showed a linear relationship between G′ and farinogram peak height with slope = 1.07.     

Refrigerated dough quality: effect of environment and genotypes of hard red spring wheat

Refrigerated dough products use wheat flour as their primary ingredient, so the quality and chemical composition of the flour determine the quality of the final product. Six varieties of hard red spring wheat, grown in 3 locations in Minnesota, U.S.A., were evaluated for use in refrigerated dough products. Total arabinoxylan percentages in the flours ranged from 0.97 to 1.54. Xylanase activity of the flour was measured and ranged from 0.20 to 0.84 mU/g. An important factor in the suitability for refrigerated dough is the syruping during storage. A large amount of variability in dough syruping was observed among the varieties and locations when the extent of dough syruping was measured over a period of 10 d. The mean dough syruping on day 10 ranged from 2.05% to 14.83%. Despite the significant interaction effect of genotype and environment, 2 varieties, Glenn and Oklee, had lower dough syrup formation with greater stability across growing locations and storage days than other varieties. Practical Application: Refrigerated dough production is one of the fastest growing segments of the ready-to-use food industry. Well-formulated and processed refrigerated doughs are practical to consume and should stay fresh during extended periods of storage; thus, maintenance of dough quality during refrigeration is critical. This study was designed to perform the research on genotypic and environmental effects on variations in dough syruping during refrigeration storage of doughs from hard red spring wheats.     

A farinograph study on the viscoelastic properties of sago/wheat flour dough systems

Doughs containing mixtures of sago and wheat flours of differing protein content at different levels of sago substitution (10, 15, 20, 25, 30, 40 and 50%) were prepared as follows: sago + high protein wheat (HPW) flour, sago + medium protein wheat (MPW) flour and sago + low ? protein wheat (LPW) flour. The viscoelasticity of doughs from control sago and wheat flours and sago/wheat flour mixtures was determined using a Braberder farinograph. It was found that arrival time increased with increasing protein content in the mixture. Peak time for control wheat flours and sago/wheat flour mixtures increased with increasing protein content. Dough stability, 20 min drop and water absorption were found to decrease as the sago proportion in the mixture decreased. The 50% sago/LPW mixture was unable to form a dough. Breakdown times for control HPW flour and HPW flour mixtures were the highest, followed by MPW flour and then LPW flour. However, breakdown time for control MPW flour was higher than that for HPW flour mixtures. The same trend was observed at all ratios of mixture over the whole experiment. Copyright © 2004 Society of Chemical Industry     

INFLUENCE OF THE STARCH GRANULE SURFACE ON THE RHEOLOGICAL BEHAVIOUR OF WHEAT FLOUR DOUGH

The influence of the properties of the starch granule surface on the rheological behaviour of wheat flour doughs was studied in dynamic oscillation measurements (frequency sweep and strain sweep) and in stress relaxation measurements. A flour with a high protein content (15%) was diluted with wheat starch to obtain a protein content of 10%. The granule surface of the substituted starch was modified in three different ways: by heat treatment, by adsorption of a wheat protein fraction and by adsorption of lecithin to the granule surface. The effects of these modified starches were compared with the results obtained for nonmodified starch and protein or lecithin (in liposomes) added to the flour. Owing to the low concentration of the added protein and lecithin, no effect was observed when they were added to the bulk of flour. However, as a starch-surface modification the same components influenced the rheological parameters studied. Also the heattreated starch had an effect on the rheological behaviour. The study established the importance of the properties of the starch-granule surface in wheat flour dough.     

Comparison of lipid effects on structural features of hard and soft wheat flour proteins assessed by front-face fluorescence

Front-face fluorescence was used to assess changes in the structural features of proteins in wheat flour dough upon addition of different exogenous lipids. Structural changes resulting from the solvation of proteins and from the mechanical deformation of proteins in dough or dough containing lipids were measured. The effects of lipid type and addition on changes in overall protein surface hydrophobicity were estimated by titrating soft and hard wheat flours, mixed with water and varying the lipid levels, with increasing concentrations of the fluorescence hydrophobic probes 1,8 anilino-napthalene-sulphonate (ANS) and thioflavin T. The lipid type and level modified the exposure of the probe to the solvent. The effects of lipids were more apparent with soft wheat flour having low-affinity hydrophobic sites on the protein surface. The dough was then characterized upon consistent mixing and physical modification in the farinograph at constant water and ANS/thioflavin T concentration, while varying the type and amount of lipids. Lipid-dependent shifts toward longer wavelengths in the probe fluorescent emission with low-protein flour suggest differences in protein coating effects related to lipid structure and protein quality.     

Suitability of various australian wheats for chinese-style steamed bread

Three methods of preparation of steamed bread on a laboratory scale were evaluated to determine the one most suitable for discriminating between flour samples. The preferred method was then applied to a number of wheat varieties at different protein levels to select the most suitable ones for this product, and to determine the key analytical parameters of the most suitable flour. Flour colour and protein content appeared to be more important than other physical and chemical properties. Flour samples with high protein content (greater than 12%) and strong doughs gave bread with a wrinkled surface and dark colour, whereas low protein (less than 10%) soft wheat flours gave poor texture and eating quality, although the surface was smooth. It is suggested that flours of medium protein content (10–12%) and medium dough strength are the most suitable for steamed bread. Processing conditions affected steamed bread quality. Blending of high protein hard strong wheats with soft weak wheat could be practical for preparing flour for steamed bread.     

The rapid non-enzymic determination of damaged starch in flour

A rapid non-enzymic method for the measurement of damaged starch in wheat flour is described. The method is based on the iodometric determination of extractable amylose. A comparison with damaged starch values obtained using an enzymic method showed that the correlation between the non-enzymic and enzymic methods was better for flours milled from soft wheats than for flours milled from hard wheats. The relationship between starch damage values obtained by the two methods and flour particle size is examined, the results suggesting that the two methods differ in their sensitivity to the type of damage suffered by hard wheats during milling.     

Changes of chemical composition and dough rheology in two fractions of sieve-classified Polish spring wheat flour

The study of chemical composition and dough rheology changes in sieve-classified two fractions (up to 60 and 60-240 microm particles) of wheat flour was the subject of this study. The straight grade flours were obtained by the milling of three Polish varieties of spring wheat, differing in particle size index (PSI) values. The flours were separated with the use of an SZ-1 laboratory sifter. The yield of fine fraction was in the range 50.0-55.7%. The obtained fractions were assayed for the content and composition of free lipids, gluten proteins, damaged starch, ash, water absorption and amylograph viscosity. Dough rheology (extrusion in OTMS cell, alveograph and farinograph tests) and baking trials were also performed. The content of free lipids, including the non-polar and phospholipids was lower and the content of glycolipids was higher in fine flours. Those fractions were more rich in linoleic acid but the lower content of oleic and linolenic acids resulted in a higher oxidizability index of free lipids. Fine flours contained less ash and significantly more damaged starch. At the same time, they were characterized by a higher content of wet gluten, water absorption, amylograph viscosity and better dough parameters. This was reflected in the bread volume, which was higher by 6.3-10.7%. The influence of the changes in composition and the content of free lipids upon the rheology of the dough after the 90 days flour storage has not been defined unambiguously and requires further research.     

Flour lipids and their effects in baking

Wheat flour lipid was separated into five fractions by selective elution from silica gel. The two earlier eluted fractions, which contained mainly non-polar components, depressed loaf volume when added to defatted flour. The three other fractions contained polar components and these maintained or increased loaf volume. The effects of the fractions as foam stabilizers paralleled their effects on loaf volume, supporting the theory that flour lipids exert their action in baking through their role as surfactants in stabilizing or destabilizing the gas bubble structure during expansion of the loaf. Evidence points to a classification of flour lipids into three groups according to their effects in baking. The polar galactolipids and phospholipids increase loaf volume, compounds of intermediate polarity depress loaf volume while the more non-polar compounds such as triglycerides have little effect in the absence of other lipids but have beneficial effects when other lipids are present. Thin-layer chromatography showed clear differences in composition between lipid extracts from wheat, rye and maize flours and these could be correlated with effects on the baking behaviour of defatted wheat flour.     

Changes of chemical composition and dough rheology in two fractions of sieve‐classified Polish spring wheat flour

The study of chemical composition and dough rheology changes in sieve‐classified two fractions (up to 60 and 60–240 μm particles) of wheat flour was the subject of this study. The straight grade flours were obtained by the milling of three Polish varieties of spring wheat, differing in ?? abbreviation? (PSI) values. The flours were separated with the use of a SZ‐1 laboratory sifter. The yield of fine fraction was in the range 50.0–55.7%. The obtained fractions were assayed for the content and composition of free lipids, gluten proteins, damaged starch, ash, water absorption and amylograph viscosity. Dough rheology (extrusion in OTMS cell, alveograph and farinograph tests) and baking trials were also performed. The content of free lipids, including the non‐polar and phospholipids was lower and the content of glycolipids was higher in fine flours. Those fractions were more rich in linoleic acid but the lower content of oleic and linolenic acids resulted in a higher oxidizability index of free lipids. Fine flours contained less ash and significantly more damaged starch. At the same time, they were characterized by a higher content of wet gluten, water absorption, amylograph viscosity and better dough parameters. This was reflected in the bread volume, which was higher by 6.3–10.7%. The influence of the changes in composition and the content of free lipids upon the rheology of the dough after the 90 days flour storage has not been defined unambiguously and requires further research.     

Distribution of soft wheat kernel lipids into flour milling fractions

Samples of whole and manually degermed Atou wheat were milled on a micro-mill to give straight-run flour, coarse offal, fine offal, finished bran and bran finisher flour. The non-starch lipids in these products were compared with non-starch lipids in the aleurone-free starchy endosperm, and with lipids in the germ and aleurone of the original wheat. About half of the triglyceride in flour was derived from the germ; no glycolipids or phospholipids were derived from germ, and no lipids of any kind were derived from the aleurone. Non-starch lipids in the aleurone-free endosperm of a mixed English soft wheat grist were then compared with the non-starch lipids in 11 flour streams from a commercial mill. All flours had much more triglyceride than the endosperm. In flours from the reduction system there were significant correlations between flour colour grade, sterylester, triglyceride, diglyceride, free fatty acid and diacylphospholipids, but none between ash or protein and colour or any class of lipid. Analysis of the principal components of variation in a simplified matrix describing all 11 flours placed triglyceride, diglyceride, free fatty acid, and diacylphospholipids close together in one group, and all glycolipids and N-acylphospholipids in a separate unrelated group. Sterylester and colour were loosely associated with the first group but could also be regarded as part of a third loose group with ash and protein. The results are interpreted in terms of lipid distribution within the wheat kernel, and their significance in milling and baking practice.     

QUALITY ATTRIBUTES OF CANADIAN HARD WHITE SPRING WHEAT

Quality characteristics of five pilot‐scale milled Canadian hard white spring wheats were compared to a No.1 grade commercial composite Canada Western Red Spring (1CWRS) wheat. One metric ton of samples was milled on the Canadian International Grains Institute pilot Buhler mill (Buhler AG, Uzwil, Switzerland) into straight‐grade (SG), 85% and whole wheat flours. At the SG extraction level, the white wheats with their lighter colored seed coats had improved milling yields (up to 2.6%) and lower ash (0.01–0.09%) than the 1CWRS control wheat. Majority of white wheat flours had higher protein contents than the 1CWRS control flours for all flour extractions. Based on dough rheological properties of the flours, three of the white wheats (Kanata, Snowbird and BW 275 ) were equal to or better than the red 1CWRS control for nearly all farinograph and mixograph parameters at all flour extractions other than farinograph absorption. Two of the white wheat lines (RL 4863 and RL 4858 ) had excessively weak and overly strong dough properties, respectively. Evaluation of pan bread, bagels and tortillas showed that white wheats generally produced end‐products that were comparable or superior to 1CWRS and that their most significantly positive quality compared to 1CWRS was their substantially lighter colored end‐products.     

Evaluation of the brabender quadrumat junior experimental flour mill for routine wheat testing

An automatic laboratory wheat-flour mill has been tested during four years with a range of New Zealand wheat varieties and qualities. Yields of flour and the usual analyses of the flours have been determined. It is concluded that the flour produced is sufficiently similar to that from an Allis-Chalmers experimental mill to be suitable for a large-scale wheat quality testing programme. The only important difference was in mixing tolerance of doughs from the two kinds of flours. Yield of flour from the mills was severely reduced as wear occurred during four years of testing.