紫薯冰皮月饼的皮料工艺研究

[目的]研究以紫薯做为皮料加工制作冰皮月饼的最佳皮料工艺配方。[方法]对冰皮月饼的传统加工工艺进行改革,在皮料制作中加入紫薯,通过单因素与正交试验,确定以紫薯作皮料生产冰皮月饼的最佳工艺配方。[结果]试验表明,影响紫薯冰皮月饼皮料品质的主次因素依次为:牛奶添加量、澄面(小麦淀粉)添加量、紫薯泥添加量、糯米粉添加量、粘米粉添加量;皮料的最佳工艺配方为:糯米粉40 g、粘米粉40 g、澄面25 g、紫薯泥40 g、牛奶185 g、糖粉50 g、色拉油20 ml。[结论]此法制作的紫薯冰皮月饼皮料感官性状良好,颜色偏紫,新颖独特,具有一定的市场潜力。     

Crystallinity changes in wheat starch during the bread-making process: Starch crystallinity in the bread crust

The crystallinity of starch in crispy bread crust was quantified using several different techniques. Confocal scanning laser microscopy (CSLM) demonstrated the presence of granular starch in the crust and remnants of granules when moving towards the crumb. Differential scanning calorimetry (DSC) showed an endothermic transition at 70 °C associated with the melting of crystalline amylopectin. The relative starch crystallinity, as determined by X-ray and DSC, from different types of breads was found to lie between 36% and 41% (X-ray) and between 32% and 43% (DSC) for fresh bread crust. Storage of breads in a closed box (22 °C) for up to 20 days showed an increase in crust crystallinity due to amylopectin retrogradation both by X-ray and DSC. However, DSC thermograms of 1-day old bread crust showed no amylopectin retrogradation and after 2 days storage, amylopectin retrogradation in the crust was hardly detectable. ¹³C CP MAS NMR was used to characterize the physical state of starch in flour and bread crumb and crust. The intensity of the peaks showed a dependence on the degree of starch gelatinization.     

沙坡头地区防护体系建立过程中生态环境变化的特点

本文主要揭示沙坡头地区流动沙丘经人工措施固沙后，生态环境条件变化的特点，如沙丘由动态状况逐渐稳定的过程，沙土发育及沙面结皮的形成因素，过程及特征；沙层含水量的变化趋势及对防护体系的影响。     

Effects of seedbed structure and water content at sowing on the development of soil surface crusting under rainfall

This study was carried out to observe the dynamics of crust formation on the soil surface under field conditions and analyse the effects of seedbed structure and water content on soil surface crusting. Seedbed sensitivity to crusting was also estimated in the laboratory by stability tests on aggregates. We observed 57 plots during the sowings of spring and autumn crops in fields in Northern France (Estrees-Mons, 50°N latitude, 3°E longitude). The soil is an Orthic Luvisol according to the FAO classification (0.17–0.25 g g⁻¹ clay and 0.02 g g⁻¹ organic matter on average). Visual assessments in situ were performed and photographs taken of crust stages on delimited areas, each 5 mm of cumulated rainfall since sowing. In 2004–2005, the seedbeds were characterised by their distribution of aggregate sizes and tests of aggregate stabilities of surface samples kept with their water content at sowing. A penetrometer was used to measure crust resistance and estimate its thickness. These data were analysed to detect the cumulative rainfall values needed for the initiation and development of the successive stages of crusts. A fully developed structural crust (stage F1) required 13, 22, 27 mm cumulated rainfall respectively for seedbeds with proportions of clods over 2 cm ranging from 0 to 0.15 (fine seedbed), 0.15 to 0.30 (medium seedbed), >0.30 g g⁻¹ (coarse seedbed). Aggregate stability measured on samples kept at sowing water content was low for soil with low water content (<0.17 g g⁻¹) but increased sharply for water contents over 0.17 g g⁻¹. Stage F1 was reached more rapidly (only 11 mm versus 19 mm cumulated rainfall) only for fine seedbeds with less than 0.15 g g⁻¹ of clods over 2 cm and with a low water content at sowing, The stage of 50% of soil surface covered with sedimentary crusts was reached for 85 mm for fine seedbed versus 120 mm for medium seedbed. The mean penetrometer resistance of dry crusts was 0.55 ± 0.43 MPa for stage F1 and 3.54 ± 0.83 MPa for a sedimentary stage; mean penetrometer resistance increased continuously with cumulated rainfall and was much lower for wet crusts. These quantitative data gathered under field conditions constitute the first step towards the prediction of soil surface crusting. The cumulative rainfalls were used in order to estimate the risk of occurrence of structural and sedimentary crusts forming during crop emergence with several types of seedbeds.     

Swelling of biocrusts upon wetting induces changes in surface micro-topography

In most of non-vegetated areas from drylands, soils are colonized by biocrusts, and although they represent a small fraction of the soil profile, they strongly affect several soil surface properties, such as porosity, available nitrogen and carbon content, hydrophobicity or micro-topography. The influence of BSCs on these soil properties has effects on numerous ecosystem processes, including water retention and runoff generation. Previous studies on the hydrological and erosive response of soils covered by biocrusts have highlighted the role of soil surface roughness as a key variable for understanding the influence of biocrusts on runoff and erosion, but biocrusts' effects on surface micro-topography varies depending on crust water content. Biocrusts can absorb large amounts of water in a short period of time, increasing their volume and modifying surface micro-topography, this change depending on biocruts type and development. A correct characterization of these surface variations may increase the knowledge about hydrological response of biocrusts, and for this reason, accurate ground level measurements of biologically crusted surfaces are essential. The objective of this study is to analyze the effect of wetting on surface micro-topography of biologically crusted soils. To achieve this objective, different crust types were scanned in the laboratory with high resolution laser scanner. Five samples were collected for each of the 4 different crust types (bare soil, cyanobacteria biocrust, and two different lichen biocruts). Two different scans were made in each sample, in dry and wet conditions. Random roughness (RR) was calculated for data from every scan, and the RR indexes obtained before and after wetting were compared. According with our initial hypothesis, an increase in surface height and surface roughness up to 0.24 and 0.20 mm respectively was observed in more developed lichen biocruts, under wet conditions respect to dry ones. These differences, despite being very subtle, could exert strong implications on runoff generation, and water evaporation, and show the complex interactions between biocruts, surface micro-topography and water fluxes.     

Combining local pressure and temperature measurements during bread baking: insights into crust properties and alveolar structure of crumb

Improvements in both the miniaturisation and heat compensation of pressure transducers made it possible to measure pressures as low as 5 kPa inside bread dough during baking (ΔT = 80 °C). Additional calibration was found to be necessary to decrease it below 0.18 kPa according to the variations in temperature encountered during baking. Two probes with both a thermocouple and a miniature pressure transducer were used to reveal pressure gradients inside bread dough during baking and post-cooling. During baking, increase in pressure (up to 1.1 kPa) was mainly attributed to the mechanical restrictions exerted on the dough by the stiffened surface layers. Pressure build-up due to the stiffening of bubble walls could not be detected. Various effects of the rupture in the bubble walls are reported. Sudden falls in pressure observed up to 70 °C were attributed to the bubble coalescence phenomenon. Evidence of an open porous structure was provided by the balance in pressure through the dough before the end of baking and the almost simultaneous lowering of pressure (−0.15 kPa) throughout the crumb during cooling. The slight lowering of pressure during post-cooling was also evidence of lower permeability of the crust compared to the crumb.     

Simulating the formation of bread crust in a DMTA rheometer

Water evaporates very fast from the surface layers of dough, enhanced by high heating rates at the beginning of baking. The rheological properties of the surface layers play an important role during the baking process, especially in local and overall expansion and water loss. The aim of this study was to determine the rheological properties of bread dough in the heat-moisture dynamics of the baking process, especially in surface drying and delayed drying conditions. The DMTA method was used in tensile mode in order to expose the samples to fast dehydration to simulate real bread crust. The degree of starch gelatinization was demonstrated by the disappearance of the “Maltese cross” (polarized light microscopy). Temperature and water content were monitored during baking. The modulus evolution depended on both the heat and moisture evolution (i.e. immediate or delayed in the present study). In contrast to reports in the literature, starch gelatinization was observed even under drying conditions. Nevertheless, comparison between samples under drying and under delayed drying conditions suggested that water content prevailed in the rheological changes.     

Lithological properties and weathering response on badland hillslopes

Rills and rill networks are important geomorphological features in clay-rich badland areas. Rill network geometry varies with climate and topography, but the lithological properties are also critical. Rill systems on mudrock and sandstone in Alberta badlands were studied to examine progressive changes in material properties as smectite-rich mudrocks and sandstones undergo weathering, and the impact of seasonal changes in precipitation patterns. Three plots with well developed rill systems on each unit were examined in May 2001 and 2003. Geometric properties were determined along a dense grid and surface and subsurface samples were analyzed for texture, crust structure (SEM), mineralogical composition (XRD), content of major elements (XRF), aggregate stability, and moisture content. The rill width/depth ratio decreased from 2001 to 2003 on mudrock rill networks. The “popcorn” crust found in 2001 changed to a thin dense crust in 2003. 2001 materials had higher Na and Ca concentrations and the 2003 materials have higher Al, K concentrations. Unweathered mudrock shards were subjected to incremental weathering in controlled laboratory conditions. Depending on moisture input, different crust types developed on materials after 10 wetting–drying cycles. Material responded to different amounts of precipitation by alteration from swelling to dispersion.     

The role of the gluten network in the crispness of bread crust

Crispness features of baked products strongly determine consumer acceptability. For many baked products, such as bread, the outer crust gives the crispy sensation. Confocal scanning laser microscopy of the structure of bread crust revealed a continuous protein phase and a discontinuous non-gelatinized starch phase in the outer crust. In contrast, the crumb and inner crust, showed a gelatinized starch network associated with a protein network. The role of the protein phase of the outer crust in determining crispness has been studied. During storage, the crispness of bread crust alters as a result of changes in water content/activity resulting from moisture redistribution within the bread and between the bread and its environment. Water content was affected by the flour protein content and by selectively modifying the crust protein phase of a model bread with enzymes, as well as by storing breads at high and low relative humidity (80–40% RH). Protease modification resulted in a lower water content and activity in the crust during the first hours of storage. In contrast, modification by transglutaminase had the opposite effect and gave rise to higher water retention of the crust compared to the un-treated d bread. This shows that modification of the protein network can be used to regulate the water holding capacity of the crust. Sensory analysis confirmed the retention of crispness in protease modified bread crust after 2 h storage at 80% RH conditions, whereas both the untreated and transglutaminase-treated breads lost their crispness. A negative relationship between water activity/content and crispness was found. Modification of the starch phase of the crust by alpha-amylase produced a bread crust with a low water activity. However, a steep increase in the water activity was observed after 2 h storage at 80% RH with a concomitant loss of crispness. These results indicate an important role of the gluten network in determining crust properties.