The effect of gluten on the retrogradation of wheat starch

The retrogradation of amylopectin in a wheat starch and a wheat starch/gluten (10:1) blend prepared by extrusion and containing 34% water (wet weight basis) was studied using X-ray diffraction, differential scanning calorimetry and NMR relaxometry during storage at constant water content and temperature (25 °C). For both samples, amylopectin ‘fully’ retrograded after 2–3 days storage, i.e. the different parameters monitored with time to follow the retrogradation had reached their maximum value, and crystallised predominantly into the A polymorph. Under the experimental conditions used, there was no evidence of any significant effects of the presence of gluten on the kinetics, extent or polymorphism of amylopectin retrogradation.     

Molecular mobility in model dough systems studied by time-domain nuclear magnetic resonance spectroscopy

The microscopic distribution and dynamic state of water and molecular mobility in various model systems are investigated using time-domain NMR spectroscopy. Starch and gluten showed different continuous distribution populations in T₂₁ (μsec range, obtained from One pulse experiments) and T₂₂ (msec range, obtained from CPMG experiments) proving that starch and gluten have different water dynamics and molecular mobility. A starch/gluten mixture (76:12, w/w) and wheat flour dough exhibited similar patterns indicating that water and molecular mobilities in dough tended to be more representative of interactions with starch than gluten, even though both water–starch and water–gluten interactions are occurring in wheat flour dough. Increasing the water content did not influence the continuous distribution pattern of T₂₁ but affected the relative amount of each fraction in T₂₁ (i.e. an increase of the more mobile fraction and a decrease of the less mobile fraction with increasing moisture). Added water has an important role in the more mobile fraction but not in the less mobile fraction, which is in μs range. This indicates that model food systems contain multiple microstructural domains with various water and molecular mobilities that show correspondingly different water dynamics. Therefore, the dispersion of various relaxation time constants helped identify the distribution of independent microstructural domains. The manipulation of the composition of the model food system influences the water dynamics and molecular mobility and provides a basis for the application of the microstructural domain concept to real food systems.     

The effect of chitosan oligosaccharides on bread staling

The aim of this work was to investigate the effects of chitosan oligosaccharides and chitosan on the rate of staling and properties of bread crumb and crust. Rates of crumb firming varied with storage time. The possible mechanisms including prevention of amylose–lipid complexation, acceleration of dehydration from both starch and gluten, adsorption of chitosan onto the starch surface and increase of moisture migration rate from crumb to crust are proposed and analysed. Chitosan oligosaccharides and low molecular weight chitosan increase bread crumb staling rate to a much lesser extent than does middle molecular weight chitosan.     

鲜食糯玉米及其亲本贮藏过程中淀粉回生特性的研究

以自主选育的鲜食糯玉米杂交种珍珠糯18、珍珠糯28及其自交系NA8066、NB1022、NB8126为试验对象,采用差示扫描量热仪(Differential Scanning Calorimeter,DSC)、低场核磁共振仪(Low field-nuclear magnetic resonance,LF-NMR)和质构仪等分析玉米样品在贮藏过程中淀粉回生及食用品质的变化情况。结果表明,随着贮藏时间的增加,鲜食糯玉米的回生度逐渐增加;T₂₁弛豫峰面积逐渐下降,T₂₂弛豫峰面积逐渐上升;玉米子粒硬度呈上升趋势。通过回生度和水分分布状态分析可以看出,珍珠糯18和珍珠糯28回生度的差异可能与父本的不同有关。相关性分析显示,所测试的5个玉米样品中,回生值均与T₂₁弛豫峰面积呈极显著负相关,与T₂₂弛豫峰面积呈显著正相关,不同品种子粒硬度与子粒表皮脆度的相关性高于与回生值的相关性,表明水分弛豫峰面积相对于子粒硬度更适宜作为鲜食糯玉米回生情况的预测手段。     

Dynamic water vapour sorption in gluten and starch films

Water sorption of gluten and wheat starch films as a function of water activity was studied using gravimetric step-change sorption experiments. Films of different thicknesses were used with the aim to vary the characteristic diffusion time and to get insights in the contribution of the polymer-chain rearrangement in the sorption behaviour. It is shown that both starch and gluten are in the glassy state for a water activity a_w below 0.9. From comparison of the dynamical sorption curves with a Fickian diffusion model, it is shown that water diffusion in gluten films seems Fickian for a_w < 0.7, and non-Fickian for a_w > 0.7, while for starch films, non-Fickian sorption behaviour is observed for a_w > 0.1. The results show that polymer-chain rearrangement and the stress built up in the matrix play an important role in the sorption dynamics of these films. Even when the material is in the glassy state matrix relaxation phenomena play a role in the sorption behaviour of starch and gluten.     

Properties of bread made from frozen dough containing waxy wheat flour

The quality of bread made from frozen dough is diminished, and staling rate is increased by changes that occur during freezing and storage. New cultivars of waxy wheat flour (WWF), containing higher levels of amylopectin, may help improve the quality of baked products. Bread quality and staling were investigated for bread containing 0–45% WWF and 55–65% water after freezing and 90-day frozen storage. The specific volume was highest with 15% WWF substitution and 60% water in bread made from both unfrozen and frozen dough. With higher levels of WWF and lower water content, bread staling rates decreased. Bread with higher levels of WWF were darker and had greater color variation. ¹H NMR studies showed that bread with greater WWF and water had higher transverse relaxation (T₂) times (9–11 ms), but less change in T₂ during storage. This research demonstrated that specific combinations of WWF and water produced a better quality of bread after dough freezing.     

Application of two-dimensional cross-correlation spectroscopy to analyse infrared (MIR and NIR) spectra recorded during bread dough mixing

During dough mixing chemical, biochemical and physical transformations occur that allow dough formation to be characterized by common chemical and biochemical methods. Recently, spectrometric methods were used to characterize the dough mixing. The Mid-infrared (MIR) and the Near-infrared (NIR) spectroscopy allow information concerning chemical content and composition of food products to be obtained. The aim of this study is to apply FT-NIR and FT-MIR spectroscopy to monitor dough chemical changes, and to correlate those signals by the 2D Cross-Correlation (2D CORR) method. The 2D CORR was used to emphasize chemical assignment of the NIR band modifications (particularly for protein) during dough mixing.The 2D CORR analysis of the raw NIR and MIR spectra demonstrated that five NIR regions are highly correlated to protein vibrations. The 2D CORR analysis of the NIR and MIR spectra after second derivative demonstrated that the amide bands present high R² for the NIR bands at (1189–1216), (1351–1474) and (1873) nm. A low R² is obtained between the amide I and amide II bands and the (2026–2123) and (2280–2325) nm regions. The amide III band presents a slightly higher R² for those NIR regions.The 2D CORR analysis of NIR and MIR spectra allow more specific NIR regions associated to chemical modifications of protein structure to be identified. The 2D CORR analysis of the second derivative spectra is more precise for the identification of the NIR regions implied in dough mixing compared to the 2D CORR analysis of raw NIR and MIR spectra.     

Effect of Genotype,Environment and Their Interaction on Quality Parameters of Wheat Breeding Lines of Diverse Grain Hardness

Abstract

Understanding the contribution of genotype, environment and genotype-by-environment interaction to wheat grain quality facilitates the selection for quality in breeding programs. Stability of grain quality characteristics is an important requirement in the baking industry. We assessed 24 winter wheat genotypes with different grain hardness in multienvironment trials at four locations and two levels of fertilization in each location. Grain samples were analyzed for hardness, protein and starch content, and wet gluten content, Zeleny sedimentation value, alveograph parameter (W) and hectoliter weight. All parameters were evaluated on whole grains using the near infrared transmittance technique. Differences between hard and soft genotypes appeared to be significant, apart from grain hardness, for protein content, Zeleny test and alveograph parameter. Genotype was found to have a major influence only on grain hardness; for protein content, wet gluten and Zeleny sedimentation value environment prevailed the influence of genotype, and for starch content, alveograph W parameter and hectoliter weight both sources of variation had similar importance. Genotype-by-environment interaction was of smaller size relative to genotype and environment in terms of all the studied quality parameters. Stable genotypes predominate the breeding lines studied. Response of unstable genotypes to environmental conditions was nonlinear in most cases.     

The effect of particle size of wheat bran fractions on bread quality – Evidence for fibre–protein interactions

The nature of the adverse effects of wheat bran fractions on bread-making quality was studied. Two fractions of bran, representing different tissue layers and having different compositions, were used. The particle size of the bran fractions was varied by various milling techniques. All fractions were added to white flour and water addition was adjusted to obtain dough with a constant consistency.     

面筋蛋白对小麦粉理化性质及面包烘焙品质的影响

为明确不同类型小麦的面粉改良方案,为我国优质面包专用粉的生产提供理论与技术支持,以三个筋力不同的小麦品种宁麦13、扬麦16和郑麦9023为材料,通过洗面筋法提取各供试材料的湿面筋,将其冷冻干燥后按照7%、8%、9%、10%、11%的添加比例与各自面粉进行配比,对配粉的面包烘焙品质、面粉理化性质和面团流变学特性进行了测定分析。结果发现,随着面筋蛋白添加量的提高,配粉的蛋白质、湿面筋、谷蛋白大聚体(GMP)含量和沉降值逐步上升;粘度参数和面团弱化度有所下降;糊化温度和糊化时间呈上升趋势。在同一添加量下,强筋小麦的烘焙品质和面粉理化性质始终优于中筋小麦和弱筋小麦。随着面筋蛋白添加量的提高,面包体积、弹性、回复性、内聚力增大,而硬度、咀嚼性减小,感官品质得到改善。面筋蛋白添加量超过一定范围(宁麦13、扬麦16添加9%,郑麦9023添加8%),面包品质改良效果变缓,且色泽不断加深。综上所述,适量添加面筋蛋白可改变面粉的理化性质,提高其面包烘焙品质;配粉的蛋白质含量为18%左右是最经济的面包烘焙品质改良方案。     

Waxy durum and fat differ in their actions as improvers of bread quality

Fat is commonly added to bakery products to improve eating qualities and extend shelf life. Flour milled from waxy durum grain was incorporated into bread formulations and its effects on crumb softness and loaf volume compared to those of added fat. Low levels of fat (0.1-0.3% of flour weight) softened the bread crumb and increased loaf volume. Most of the softening effects were evident in the crown of the loaves protruding above the tin and a high proportion of the reduction in compression was associated with increased volume. Loaves baked with waxy durum flour were softer than those baked with fat and the softening effects were evident both in the crown of the loaf and at its base where it had been confined within the tin. Waxy durum flour reduces compression independently of increased volume. It is suggested waxy durum flour acts by slowing the migration of water from the gluten phase to the starch phase so maintaining the level of mobile water in the gluten where it acts as a plasticiser. Independent organoleptic assessment of bread quality baked with combinations of waxy durum and fat confirmed the quality enhancing effects of waxy durum flour.     

Amylases and bread firming – an integrated view

Despite much research, bread crumb firming during storage and amylase anti-staling properties are still ill understood. We present a coherent view on the topic based on literature, experimental data, and food polymer science-related concepts. During bread storage, the gelatinised starch (amylopectin) network, present in soft, fresh bread, is gradually transformed into an extensive, partially crystalline, permanent amylopectin network, with amylopectin crystallites acting as junction zones. This network increasingly accounts for the bulk rheological behaviour of aging bread crumb. Furthermore, as amylopectin retrogradation proceeds, moisture migration within the crumb structure occurs, and more and more water is immobilised within amylopectin crystallites. The crystalline hydrate water can no longer plasticise the different networks, which goes hand in hand with increased crumb firmness and decreased crumb resilience, due to a less flexible gluten network. The efficiency of anti-staling amylases can be related to the extent they limit the formation and the strength of the permanent amylopectin network, and the water immobilisation. Conventional alpha-amylases weaken the amylopectin network by cutting the long polymer chains connecting the crystalline regions, but have little effect on amylopectin recrystallisation. In contrast, maltogenic alpha-amylase primarily shortens the amylopectin side chains, thus hindering amylopectin recrystallisation, and the concomitant network formation and water immobilisation.