Effects of ingredients on the oxidation of linoleic acid by lipoxygenase in bread doughs

Flour and water doughs containing 1-¹⁴C-linoleic acid (18:2) and various ingredients were prepared to study the oxidation of linoleic acid by lipoxygenase in bread doughs. Lipids were extracted, treated with diazomethane, and ¹⁴C-labelled fatty acid methyl esters separated by thin-layer chromatography. Radioactivity was determined in silica gel bands containing unoxidised 18:2, hydroperoxy acids (L₁), hydroxy acids (L₂), hydroxyepoxy acids (L₃) and trihydroxy acids (L₄). Minor components detected by autoradiography were present mainly in L₃ and L₄. Recoveries of total radioactivity were always > 95%. Untreated flour-water dough was mixed aerobically for ?4 min, rested, and the lipids extracted after 10 min total dough time. Yields of ¹⁴C products were unoxidised 18:2 = 28.6 μmol, L₄ = 93.9 μmol/100 g dry flour. Similar yields were obtained from ClO₂-treated flour, both after 10 min and 60 min dough time. Salt, salt + yeast, or salt + yeast + ascorbic acid in the dough did not reduce 18:2 oxidation significantly, but increased L₃ at the expense of L₄. Soya flour preparations inhibited linoleic acid oxidation by 25–44%, but pure soya lipoxygenase had no effect at all. Heat treatment reduced the inhibitory effect of soya flour. Accessible thiol groups were not essential for lipoxygenase activity or for the reduction of L₁ to L₂ since adding cysteine or N-ethyl maleimide had negligible effects on the 18:2 oxidation products. Most of the flour carotenoids (xanthophylls) were bleached by wheat enzymes in non supplemented doughs, and all were bleached in doughs supplemented with soya flour. ¹⁴C-labelled triglyceride was not oxidised except in doughs containing soya flour mixed in air (1.5% oxidation) or oxygen (3 % oxidation). Soya flour contains lipoxygenase isoenzymes (principally lipoxygenase-2) which oxidise linoleate in triglycerides. This isoenzyme is evidently not present in wheat.     

Enhancing the Rheological Performance of Wheat Flour Dough with Glucose Oxidase,Transglutaminase or Supplementary Gluten

The enzymes glucose oxidase and transglutaminase are frequently used to improve the breadmaking performance of wheat flours, as they have the ability to considerably alter the viscoelastic nature of the gluten network. To evaluate a flour’s breadmaking performance, rheological tests offer an attractive framework. In this study, the rheological impact of adding glucose oxidase or transglutaminase to wheat flour dough is investigated by means of linear oscillatory shear tests, creep-recovery shear tests and startup extensional tests. The former tests reveal that the enzymes render the dough stiffer and enhance its elastic character, until saturation is reached. In the breadmaking process, the use of excessive amounts of enzyme is known to be counterproductive. The strain-hardening index clearly reveals this overcross-linking effect. Besides enzymes, the gluten network can also be reinforced by adding supplementary gluten, which was indeed found to enhance the extent of strain-hardening.     

Wheat Germ Lipoxygenase: Its Effect on Dough Rheology,Microstructure, and Bread Making Quality

Extracted lipoxygenase from defatted wheat germ of commercial bread wheat along with raw and defatted germ were used to study their effect on rheological characteristics of wheat flour dough and bread making quality. The addition of 500 U and 1000 U of lipoxygenase increased the water absorption from 59.5 to 62.3 and 66.7%, respectively. The dough stability increased to 10.5 min, whereas mixing tolerance index values marginally decreased, and the addition of raw or defatted germ did not affect the mixing profile of the wheat flour dough. Breads with lipoxygenase were softer with a lower firmness value of 546 g when compared to the control (594 g) and had brighter crumb as seen in the reduction in ΔE values from 22.34 (control) to 19.04. The addition of gluten along with the lipoxygenase showed a synergistic effect. The specific volume of breads increased to 3.95 cc/g and the firmness values decreased to 538 g. Scanning electron micrographs at different stages of bread processing have shown improvement in the gluten network.     

Combined effects of wheat gluten and carboxymethylcellulose on dough rheological behaviours and gluten network of potato–wheat flour-based bread

Incorporating high level of potato flour into wheat flour enhances nutritional values of bread but induces a series of problems that lead to the decline of the bread quality. To overcome the barrier, wheat gluten and carboxymethylcellulose (CMC) were added into potato–wheat composite flour to improve dough machinability and bread quality. The rheological properties, thermo-mechanical properties and microstructures of dough were investigated. The results showed that the interaction between gluten and CMC mitigated the discontinuity of gluten matrix and gluten protein aggregation caused by the addition of potato flour, which yielded a more branched and compact gluten network. The compact three-dimensional viscoelastic structure induced improvements of gas retention capacity and dough stability, making it mimic the machinability properties of wheat flour dough. Bread qualities were apparently improved with the combined use of 4% gluten and 6% CMC, of which specific volume increased by 42.86%, and simultaneously, hardness reduced by 75.93%.     

Effects of protein oxidation on the rheological behaviour of different wheat flour

Wheat flour proteins are subject to oxidation reactions during production, processing and storage. The quality of protein and the rheological properties of wheat are crucial for the flour industry. However, the impact and mechanism of protein oxidised on wheat flour quality remain unclear. In this study, ozone was used to oxidise wheat grains, the secondary structure of protein in flour and the rheological properties of dough were analysed by FTIR and Mixolab. The proportion of α-helix and β-folding of protein were decreased significantly, as were the development time (DDT), stability time (DST) and protein weakening (C2) value of dough. Meanwhile, starch gelatinisation (C3), amylase activity (C4) and retrogradation (C5) were increased significantly, along with the elastic modulus (G′) and viscous modulus (G″). Microstructure analysis indicated that protein oxidation destroyed the gluten network structure in the dough. In addition, the L* value of dough was decreased and a* and b* values were increased significantly. The results showed that the oxidation of protein reduced the stability of protein secondary structure, weakened the structure and stability of the gluten network in dough, and changed the viscoelasticity and colour of dough. Overall, these findings provide a better understanding of rheological behaviour in wheat flour.     

Effects of japonica rice flour on the mesoscopic and microscopic properties of wheat dough protein

The aim of this study was to study the effects of twelve varieties of japonica rice flour on the gluten protein composition and structure of wheat dough. Experimental results indicated that the addition of japonica rice flour significantly decreased the α-helix structure in the gluten protein sample, but increased the random coil content, indicating that the protein secondary structure became more disordered. The ratio of α-helix/β-sheet structures in the dough supplemented with different varieties of japonica rice flour was decreased, contributing to improved dough stability. Increasing the proportion of japonica rice flour from 10% to 40% significantly decreased the sulfhydryl content of the mixed flour dough. However, the total sulfhydryl content was only positively correlated with the amount of Longdao 19 japonica rice flour, reaching a maximum of 25.34 mol g⁻¹ at 40% japonica rice flour. The gluten structure of mixed flour dough typically forms a porous three-dimensional network, with the Longdao 19, 20, 23 and 25, Longjing 31 and Mudanjiang 31 japonica rice flours leading to improved gluten protein networks. In summary, the supplementation of standard wheat flour with japonica rice flour can alter dough properties and gluten structure.     

Enrichment of Bread with Nutraceutical‐Rich Mushrooms: Impact of Auricularia auricula (Mushroom) Flour Upon Quality Attributes of Wheat Dough and Bread

Edible mushrooms contain a variety of bioactive molecules that may enhance human health and wellbeing. Consequently, there is increasing interest in fortifying functional foods with these nutraceutical‐rich substances. However, incorporation of mushroom‐based ingredients into foods should not adversely affect the quality attributes of the final product. In this study, the impact of incorporating powdered Auricularia auricula, a widely consumed edible mushroom, into bread products was examined. The rheological and structural properties of wheat dough and bread supplemented with 0% to 10% (w/w) A. auricula flour were measured. Supplementation of wheat doughs with A. auricula flour increased the peak viscosity and enhanced their water holding capacity. Rapid viscosity analysis showed that peak and final viscosities of the blended flour (wheat flour with A. auricula flour) were higher than wheat flour alone. However, dough stability and elastic modulus were reduced by blending wheat flour with A. auricula flour. SEM observation showed that doughs with up to 5% (w/w) A. auricula flour had acceptable gluten network microstructure. Characterization of the quality attributes of bread indicated that incorporation of A. auricula flour at levels >5% negatively impacted bread volume, height, texture, and appearance.     

Effect of phenolic acids on the rheological properties and proteins of hard wheat flour dough and bread

BACKGROUND: The effects of different phenolic acids on the rheological properties and gluten proteins of hard wheat flour dough and bread were investigated. Caffeic, ferulic, syringic and gallic acids were each blended with hard wheat flour at a concentration of 4.44 µmol L^?1 g^?1 flour. RESULTS: Mixing time and tolerance were reduced with the addition of phenolic acids. The phenolic acids reduced the maximum resistance to extension (R_max) and increased the extensibility of dough, with effects in the following order: gallic < syringic < ferulic < caffeic acid. The effect on R_max was more pronounced in overmixed dough. Loaf volume was most significantly decreased with the addition of caffeic acid. Extraction of sodium dodecyl sulfate‐soluble high‐molecular‐weight proteins was increased in both mixed and fermented doughs by the addition of ferulic and caffeic acids. The order of influence of the phenolic acids on the rheological properties and protein structure of dough and bread was consistent with that of their antioxidant activity. CONCLUSION: The addition of caffeic and ferulic acids reduced R_max and increased the extensibility of hard wheat flour dough by modifying the high‐molecular‐weight gluten, which resulted in decreased bread volume. Copyright © 2011 Society of Chemical Industry     

苦荞粉添加量对面团性质及馒头品质的影响

通过添加不同量的苦荞粉配成苦荞-小麦混粉,研究混粉揉混特性、面团微观结构的变化以及苦荞馒头的感官品质。结果表明,当添加量在5%~15%时,揉混结果中的和面时间和峰值面积变化不大,微观结构中蛋白质面筋网络结构略微减弱,但当添加量达到20%后,和面时间和峰值面积都有大幅度降低,微观面筋网络结构也出现明显的下降。同时,苦荞粉添加量为15%时馒头感官品质较好。综合分析可知,添加量为15%时苦荞馒头仍具有较好的品质。     

The effects of different materials as dough improvers for organic whole wheat bread

In this research, the effects of different materials such as defatted Cephalaria syriaca flour (0.5%), rosehip (2.5%), vital gluten (2.5%) and malt flour (2%), and their combinations on the quality of organic whole wheat flour were investigated. The highest maximum resistance value was obtained in the treatment containing 0.5% cephalaria and 2.5% rosehip. The addition of malt flour and vital gluten significantly increased the extensibility value. Although rosehip, cephalaria and vital gluten generally increased the dough energy, malt flour decreased the dough energy when compared to the control. The combination of 0.5% cephalaria and 2.5% rosehip significantly decreased the adhesion and stringiness of dough. Data showed that dough rheological characteristics of organic whole wheat flour could be improved with the addition of different materials such as malt flour, cephalaria, rosehip and vital gluten.     

Tannins improve dough mixing properties through affecting physicochemical and structural properties of wheat gluten proteins

The quality of wheat flour is largely determined by the properties of gluten proteins. Chemical components that influence gluten proteins are used as flour improvers in the flour industry. In this study, tannins which are natural occurring polyphenols were found to improve dough mixing properties. The effects of tannins on the physicochemical and structural properties of gluten proteins were examined, and the results showed that tannins promoted the non-covalent interactions among gluten proteins, although they induced SH/SS interchange reactions in the dough. The β-turn and α-helix conformations were increased, whereas the β-sheet conformation was decreased in dough containing tannins as detected by FTIR. Moreover, the addition of tannins promoted the aggregation of gluten proteins, modified the microstructure of gluten networks, and improved the mixing properties. The positive effects of tannins on dough properties implied the potential of tannins as a new flour improver.     

The effect of lipoxygenase action on the mechanical development of doughs from fat-extracted and reconstituted wheat flours

The mechanism by which soya lipoxygenase enzyme action improves the Theological properties of wheat flour doughs during mechanical development in air has been investigated further. Free-lipid extraction, reconstitution and replacement experiments have shown that the rheological effect of lipoxygenase action, which is consistent with an oxidative improvement of the dough proteins and may also result in extended mixing tolerance, only occurred in the presence of an oxidisable, polyunsaturated, free-lipid substrate. Addition of this substrate in an oxidised state (produced either by autoxidation or enzyme-oxidation) to doughs mixed from fat-extracted flour under nitrogen resulted only in a small rheological improvement, greater for the autoxidised than the enzyme-oxidised lipid, but in no way comparable with the large rheological effect of lipoxygenase action during dough mixing in air. Furthermore, the presence of an antioxidant, nordihydroguaiaretic acid (NDGA), during dough development, although greatly inhibiting peroxide formation, only marginally impaired the rheological improvement due to lipoxygenase action. Additional evidence is therefore provided for a coupled oxidation mechanism being responsible for the rheological effect, since lipoxygenase-catalysed oxidation actively occurring in the dough during mixing appears to be the fundamental requirement, irrespective of whether the primary oxidation products lead to lipid peroxides or oxidised NDGA.     

Rheological Properties of Bread Dough Formulated with Wheat Flour–Organic Calcium Salts–FOS-Enriched Inulin Systems

The objective of this work was to study the effect of organic calcium salts–fructooligosaccharide (FOS)-enriched inulin systems on dough structure and rheological properties of wheat flour dough. Wheat flour was enriched with calcium lactate (CaLa₂) or calcium citrate (Ca₃Ci₂) (from 1,080 to 2,520 ppm Ca) and FOS-enriched inulin (In) (from 0 to 13 %, w/w flour basis). Alveographic, texture, relaxation, and viscoelasticity properties of dough were analyzed. Wet and dry gluten quantity, related to scanning electron microscopy structure, was also determined. Tenacity, extensibility, and deformation energy of dough decreased with the increment of In content. When CaLa₂ was employed, they changed mainly with fiber, hiding the effect of lactate; whereas with Ca₃Ci₂, these parameters were not only affected by the fiber, but also by the salt. At In 6.5 %, high calcium content (2,520 ppm Ca) produces an increase in hardness and a decrease in cohesiveness for citrate ion; the opposite effect was detected with lactate ion. These parameters decreased at high content of In (13 %). Adhesiveness was dependent only on In level; more adhesive dough at In?>?6.5 % were obtained, mainly in the case of CaLa₂. Ca₃Ci₂ prevents the decrease in adhesiveness at In?>?12 %. At high calcium levels, high In produced more elastic dough only in the presence of citrate; for lactate, the predominant factor was In. Lactate anion destabilizes protein structure, and together with In favors formation of a less elastic gluten network. On the other hand, the stabilizing effect of citrate ion in a firm network was enhanced by FOS-enriched inulin.     

高筋粉添加量对复配粉的糊化特性及面团流变学特性的影响

为了改善市售小麦粉(蛋白质10.3%)制作油塔子的面团特性,在市售小麦面粉(以下简称小麦粉)中添加不同比例高筋粉(蛋白质12%),测定复配粉的基本性质、糊化特性以及面团流变学特性。结果表明,随着高筋粉添加量增加,复配粉的白度显著增加(p0.05),蛋白质干基、湿面筋含量和水分均呈上升趋势,灰分变化并不显著(p0.05);复配粉的峰值黏度、最低黏度、最终黏度随着高筋粉添加量的增加而下降,在高筋粉添加量为40%时,衰减值及回升值均达到最低,为850.50 cp、1035.50 cp;添加高筋粉降低了小麦粉的面团形成时间和稳定时间,弱化程度反而升高;高筋粉添加量为40%时,复配粉的拉伸曲线面积、拉伸阻力、延伸度均为最高,分别是122.05 cm2、341.75 BU、179.30 mm。结论说明高筋粉对市售面粉粉质特性、糊化特性、面团拉伸特性均有影响,制作油塔子面团高筋粉的添加量以40%为宜。     

青麦粉添加对馒头面团及面筋蛋白结构的影响

以馒头专用粉及青麦粉制作青麦馒头,利用激光共聚焦显微镜、黏度仪、红外光谱仪等分析仪器进行测定,探究不同青麦粉添加量(0%、5%、10%、15%、20%)对面团粉质特性、糊化特性、微观结构及面筋蛋白二级结构的影响。结果表明,随着青麦粉添加量的增加,混合粉湿面筋含量、面筋指数减少;糊化温度、峰值黏度降低,面团糊化时间缩短,面团稳定时间从6.18 min降至4.92 min、粉质质量指数减小了18,面筋强度变弱,承受力变差;面团拉伸面积、延伸度和最大拉伸阻力在135 min时显著减小;面筋网络结构逐渐出现孔洞,分布不均匀;面团面筋蛋白各吸收峰都发生了偏移,β-折叠和α-螺旋结构含量增加;综上所述,青麦粉的加入改变了面团特性和面筋蛋白结构,这些变化可能是导致青麦馒头品质下降的主要原因。     

Studying the effects of whole-wheat flour on the rheological properties and the quality attributes of whole-wheat saltine cracker using SRC,alveograph, rheometer,and NMR technique

Quality attributes of soft wheat products are affected by physicochemical characteristics and rheological properties of wheat flour. Whole-wheat flour has a significant impact on baking qualities (stack height, stack weight, specific volume, and breaking strength) of whole-wheat saltine crackers due to its high water absorption capacity. SRC profiles, alveograph and rheometer parameters were determined to observe the effect of whole-wheat flour on whole-wheat cracker flour blends. NMR technique was utilized to demonstrate the water migration and competition in whole-wheat dough components. Results of SRC testing revealed that the water absorption of whole-wheat flour blends increased with the addition level of whole-wheat flour. The rheological properties (G′, G″, P, L, W values) were influenced significantly by the presence of whole-wheat flour. Results of NMR indicated that water migrated from gluten network into arabinoxylans matrix in whole-wheat dough system, resulting in inferior saltine cracker-baking qualities of whole-wheat flour, i.e., small breaking strength, stack height and specific volume. The stack height, specific volume, and breaking strength of end products showed significant correlations with the arabinoxylans, dough extensibility, and gluten index of whole-wheat flour.     

葡萄糖氧化酶和谷氨酰胺转氨酶对发酵麦麸面团加工品质的影响

本研究旨在探讨葡萄糖氧化酶和谷氨酰胺转氨酶对发酵麦麸面团加工品质的改良效果及改良机制,为改善全麦发酵食品食用品质提供应用参考。在全麦粉中分别添加1.0、3.0和6.0 U/g的葡萄糖氧化酶或谷氨酰胺转氨酶,分析测定了全麦粉粉质特性、发酵面团质构特性以及面筋的持水率、蛋白质组成和游离巯基含量的变化情况。研究结果表明:两种酶制剂的添加对全麦粉粉质特性有显著改善作用(p<0.05),面团稳定时间延长,弱化度减小;随酶制剂添加量的增加,发酵面团的弹性和凝聚性均显著增加,面筋蛋白中谷蛋白大聚合体(GMP)含量显著升高,游离巯基的含量显著减少(p<0.05),但高添加量的谷氨酰胺转氨酶(6.0 U/g)引起面筋蛋白持水率下降。谷氨酰胺转氨酶对麦麸面团品质的改良效果显著优于葡萄糖氧化酶(p<0.05),其适宜添加量为3.0 U/g,可使麦麸面团的稳定时间由5.3 min延长至9.3 min。     

马铃薯全粉在面条中的应用研究

将马铃薯全粉添加到小麦粉中,并辅助添加谷朊粉,制成马铃薯全粉面条。从质构特性、微观结构和面条的理化性质三个层面对三个不同马铃薯全粉添加比例的面条组别进行研究,发现马铃薯全粉对面团的力学性质,面筋网络的形成和构造以及面条的蒸煮参数和外观都会产生一定的影响。结果表明：马铃薯全粉添加量为20%（g/g）,谷朊粉添加为0.03%（g/g）时,总体指标最好;马铃薯全粉对面团的作用具有双向性,马铃薯淀粉对面团的影响偏负向,但是其中的多糖和蛋白质可能对面团和面筋网络有正向影响,同时谷朊粉的添加对面团的稳定性和面条的质量有改善作用。     

Mechanistic study of the impact of germinated brown rice flour on gluten network formation,dough properties and bread quality

The objective of the study was to investigate the impact of germinated brown rice flour (GBRF) on the mechanism of high gluten wheat flour (HGWF) network formation and dough properties. Therefore, dough properties, microstructures, stability mechanism and bread quality were evaluated. Results showed that HGWF+10%GBRF exhibited a higher dough stability time (DST), pasting temperature, storage modulus (G′) and loss modulus (G′′), as well as a lower compliance value. The microstructure of dough showed that GBRF interfered with the self-organization of gluten protein molecules and affected the formation of gluten network structure. The disulfide bonds and β-sheet structure were proved to play an important role in facilitating the formation of a stable three-dimensional network structure, which revealed the regulatory mechanism of GBRF in maintaining the dough stability and strength. Furthermore, the dough mixing properties and texture parameters (i.e., hardness and fracturability) of breads were significantly correlated. Overall, GBRF can be used as a potential ingredient for whole grain products and its realistic role in bread-making has been demonstrated.     

Evaluation of the processing quality of noodle dough containing a high Tartary buckwheat flour content through texture analysis

A texture analysis method for evaluating the processing quality of noodle dough with a high Tartary buckwheat flour (BF) content was established. And then the improvement of wheat flour (WF), wheat gluten (WG), and pre-gelatinized Tartary buckwheat flour (PBF) for the processing quality of buckwheat noodle dough was compared quantitatively, and the mechanism was explored through the observation of gluten network in dough sheets. Texture results showed that the coefficients of variation of tensile strength and adhesiveness of dough sheets among 16 groups were 17.76% and 40.72%, respectively, and the intragroup variation coefficients were only 4.17% and 7.07%, respectively. The tensile strength of dough sheets was significantly positively correlated with gluten index of WF and WG. In addition, with the increase of WG and PBF addition, the tensile strength and adhesiveness of dough sheets showed a linearly increase trend. Furthermore, the gluten network in the dough sheets containing WF or WG with high gluten index distributed more evenly and compactly than that with low gluten index. The dough sheet with 9% PBF showed more uniform gluten network, compared with that without added PBF. Overall, texture analysis of dough sheet can be used to evaluate the processing quality of noodle dough containing 70% BF, and the WF and WG with high gluten index had better improvement than PBF.