地衣芽孢杆菌D3.11凝乳酶对切达干酪质地特性的影响

为揭示地衣芽孢杆菌D3.11凝乳酶对切达干酪成熟过程中质地的影响,利用地衣芽孢杆菌D3.11凝乳酶制作切达干酪(CDF组)和切达干酪类似物(CD3组),采用商品凝乳酶作为对照(CCF组),分析干酪成熟过程中质构、流变特性、微观结构的变化规律.结果表明:3组干酪的硬度随着干酪的成熟而增加,而弹性和咀嚼性则呈现下降趋势,C...     

凝固型酸奶在储存过程中的特性研究

研究了凝固型酸奶在4℃储存期间粘度、总酸度和活菌数的变化规律。以发酵好的酸奶为基点保存12 d,总共7个点对酸奶的各个指标进行检测。检测表明,酸奶的粘度在储存期间是逐渐降低的,活菌数随总酸度逐渐上升而降低,而总酸度是逐渐升高的。酸奶的粘度和酸度存在一定的相关性。     

Fast X-ray tomography analysis of bubble growth and foam setting during breadmaking

The use of fast X-ray computed microtomography (CMT) shows that the development of gas cell structures during fermentation first depends on a critical time, t₁, determined by overall expansion and before which bubbles grow freely according to a simple exponential law. Afterwards, coalescence rapidly prevails and then leads to a heterogeneous structure, for t≥t₂, characterized by a continuous void phase likely to be stabilized by liquid film walls. This result confirms the involvement of minor components in addition to gluten protein for obtaining a desirable bread texture and suggests that their interfacial properties need to be investigated. The use of fast in situ CMT with careful 3D image analysis also provides data for the validation of numerical models of bubble growth. These small scale experiments could be extended to follow the rheological properties of expanding doughs and the temperature-state changes of wheat flour biopolymers which govern bread baking.     

Effect of shear rate on microstructure and rheological properties of sheared wheat doughs

Structure formation in dough systems is the result of an interplay between processing conditions and subsequent interactions in the protein phase. These interactions can be both of a covalent (disulfide bonds) and physical nature and occur at all length scales.     

Mechanism of gas cell stabilization in bread making. I. The primary gluten–starch matrix

Expansion of dough and hence bread making performance is postulated to depend on a dual mechanism for stabilization of inflating gas bubbles. Two flours were used in this study, one from the wheat variety Jagger (Jagger) and the other from a composite of soft wheat varieties (Soft). Thin liquid lamellae (films), stabilized by adsorbed surface active compounds, act as an auxiliary to the primary gluten–starch matrix in stabilizing expanding gas cells and this mechanism operates when discontinuities begin to appear in the gluten–starch matrix during later proving and early baking stages. Contributions of the liquid lamellae stability to dough expansion were assessed using flours varying in their lipid content. Incremental addition of natural lipids back into defatted flour caused bread volume to decrease, and, after reaching a minimum, to increase. Strain hardening is a key rheological property responsible for stabilizing the primary gluten–starch matrix. Jagger gave higher test-bake loaf volume than Soft and higher strain hardening index for dough. The different lipid treatments were found to have negligible effects on strain hardening index. Image analysis of crumb grain revealed that differences in number of gas cells and average cell elongation with different lipid treatments were insignificant. The evidence agrees with a dual mechanism to stabilize the gas cells in bread dough. To understand dough rheology at a molecular level, rheological properties of doughs were varied by addition of flour protein fractions prepared by pH fractionation. Fractions were characterized by SE-HPLC and MALLS. The molecular weight distribution (MWD) of fractions progressively shifted to higher values as the pH of fractionation decreased. Mixograph dough development time paralleled the MWD. However, the strain hardening index and the test-bake loaf volume increased with increasing MWD up to a point (optimum), after which they declined. At a given strain rate, the behavior at the optimum is thought to result from slippage of the maximum number of statistical segments between entanglements, without disrupting the entangled network of polymeric proteins. Shift of MWD to molecular weight higher than the optimum results in a stronger network with reduced slippage through entanglement nodes, whereas a shift to lower molecular weights will decrease the strength of the network due to a lesser number of entanglements per chain.     

Improving the mechanical characteristics of faecal waste in rainbow trout: the influence of fish size and treatment with a non-starch polysaccharide (guar gum)

This study (3 × 2 randomized factorial design) describes differences in the mechanical properties of faeces from rainbow trout of three size classes (small ≈40 g, mid-size ≈150 g, large ≈650 g) and assesses the effects of a non-starch polysaccharide binder (guar gum). Observations made at the macroscopic level were reinforced by rheological measurements of viscosity and elastic modulus. Mid-sized fish excreted mechanically the most stable faeces, roughly twice as stable as those of small fish and three times more stable than faeces from large fish. The addition of 3 g kg⁻¹ of guar gum saw some mechanical characteristics improve by about 700%. Faeces from large- and mid-sized fish were more easily stabilized than those of small fish. Mechanical recovery potential for faecal samples disrupted by water turbulence was determined. Stability differences observed for different fish size had no significant effect but the improvements imparted by guar gum reduced postfiltration effluent load to about 35% for large fish, about 24% for mid-size and about 22% for small fish. Faecal leaching decreased significantly with increasing stability. Guar gum was shown to have significant potential for improving the treatability of fish faecal waste.     

淀粉磷酸单酯对面团流变特性的影响研究

[目的]探讨不同取代度及添加量的淀粉磷酸单酯对面团粉质及拉伸特性的影响。[方法]通过控制反应时间,制备得到两种不同取代度的淀粉磷酸单酯(0.019和0.011),然后分别按面粉重量的0.4%、0.7%、1.0%添加到面粉中,研究其粉质特性和拉伸特性。[结果]面团中按1.0%添加取代度为0.019的淀粉磷酸单酯时,其面团形成时间降低为2.4 min,面团稳定时间增加到4.9 min,软化度降低到86,面团延伸度从24.27 mm提高到25.78 mm;最大拉伸力从0.024 g增加到0.049 g。[结论]淀粉磷酸单酯具有较好的增稠性、乳化性和使用安全性等特点。在弱筋粉中添加淀粉磷酸单酯,可以减少面团形成时间,提高面团稳定时间,降低了软化度,改善面团的粉质特性,淀粉磷酸单酯的取代度越高,其改善效果越好。     

小麦粉面团稳定时间的变化及其稳定性分析

 小麦的面团稳定时间是判别小麦品种类别及其用途的重要指标。本研究针对生产上小麦面团稳定时间变化很大的问题，选用山东省主要推广的12个优质小麦品种（系）为材料，在9个不同的试点上，连续3年进行了面团稳定时间变异及其稳定性分析试验。结果表明，不同品种、不同年份和地点间面团稳定时间的变异系数为24.29～49.60。利用主效可加互作可乘模型（AMMI）对面团稳定时间进行稳定性分析得知，面团稳定时间存在显著的品种和地点间的互作效应，其中品种的固定效应导致的变异最大，品种和地点互作次之，地点（含重复）效应较小。但不同品种与不同试点的交互作用不同，每个品种（系）对试点都有其特殊的适应性。因此，在优质专用小麦产业化种植时，要获得面团稳定时间达到标准的商品粮食，即要选准适宜的品种又要注意适宜的种植区域。     

小麦面团粘度与面粉主要品质指标相关性研究

以山东省32个小麦品种为材料,进行面团粘度性状和蛋白质含量、面筋指数、面团流变学特性指标之间的相关性的研究。结果表明:(1)面团的粘度性状与面粉很多品质指标具有非常显著的相关性,可以使用面团粘度性状对面粉品质进行评价。(2)面团粘度与代表面团筋力强弱的品质指标都有非常显著的负相关,说明小麦面团粘度与小麦面团的筋力强度和面团的抗揉混强度之间具有非常显著的负相关性,表明降低面团的粘度,可以提高面筋质量、面团的抗揉混能力和面筋筋力强度。     

Effects of fungal α-amylase on chemically leavened wheat flour doughs

Chemical leaveners are used in doughs to generate carbon dioxide, as an alternative to yeast, in making a range of bakery products. In this study, the effects of fungal α-amylase and ascorbic acid on chemically leavened doughs were followed by measuring dough extensibility, true rheological properties, the amount of free liquid in doughs following ultracentrifugation and the quality of baked products. As with yeasted doughs, the bake qualities of chemically leavened doughs also improved in the presence of fungal α-amylases. The bake qualities were not affected when the equivalent amount of ascorbic acid was added. The differences in dough formulations were detected from measurements of true rheological properties, not from extensibilities of doughs. The amount of free liquid was larger and of lower viscosity in doughs containing α-amylases. The properties of the continuous liquid phase were found to be important in defining the rheological and baking qualities of doughs.