Viscoelastic Properties of Extruded Cereal Melts

Hydrophilic biopolymer systems reach a state of maximum plasticization at a concentration of water designated as W_g′. The thermomechanical behaviour of various extruded cereals were investigated at concentrations above and below W_g′ to determine the significance of W_g′ on the viscoelastic properties in the rubbery region above T_g. Cereal melts were produced via extrusion cooking using a twin-screw extruder at in-barrel moisture contents ranging from 25 to 42% (wb). Dynamic mechanical thermal analysis (DMTA) was used to determine the viscoelastic properties for melts obtained from degermed corn meal, oat flour, pregelatinized corn starch and pregelatinized waxy maize. All of the extruded melts displayed reductions in the storage modulus of about two orders of magnitude from the glassy to rubbery regimes. At temperatures greater than 320K, another transition is apparent for extruded oat flour. These losses may be attributed to a reduction in physical crosslinks and/or entanglements. With respect to the other melts investigated, differences in the oat flour melts at temperatures above T_gmay be due to the increased presence of protein and lipid. Given the apparent partly crystalline nature of these melts at moisture contents <W_g′, the most appropriate representation of the viscoelastic properties may be isotimic plots of the viscoelastic functions. These contour plots provide a more comprehensive guide to material behaviour than the ‘traditional’ state diagrams found throughout the literature. An important point is that prediction of viscoelastic properties above T_gfor polymers where the internal structure changes with temperature or moisture content, cannot be predicted using the same methods of reduced variables as for amorphous polymers. Thus rather than using these methods, experimental data, such as given here, may prove to be necessary to design or understand processes involving cereal melts based on their viscoelastic properties.     

挤压膨化对绿茶茶渣中粗纤维影响

利用双螺杆挤压膨化机对绿茶茶渣进行挤压膨化加工,采用响应面设计方法建立物料含水量、喂料速度、螺杆转速以及套筒温度与绿茶茶渣中粗纤维含量之间的回归模型。结果表明,各参数对绿茶茶渣中粗纤维含量影响由大到小依次为：螺杆转速>套筒温度>喂料速度>物料含水量,获得低粗纤维含量的最佳挤压膨化参数为物料含水量70%,喂料速度90r/min,螺杆转速90r/min,套筒温度50℃。在此条件下,茶渣中粗纤维含量为15%,与膨化前原料相比,粗纤维含量下降了3%。     

Physicochemical, Structural and Textural Properties of Tortillas from Extruded Instant Corn Flour Supplemented with Various Types of Corn Lipids

The chemical composition and the components of corn grain affect the quality of tortillas produced from extruded instant corn flour (EICF). We have studied the effects of various types of corn lipids added at several concentrations to the regular raw corn flour before processing. The structural properties of flour, the effective moisture diffusion coefficient and the weight loss during cooking of fresh masa, as well as the textural characteristics of tortillas were analysed as a function of concentration and type of corn lipid added. The concentration of added lipid ranged from 0·5 to 2% (w/w). Each type and concentration of lipid was observed to have a different effect in the quality of masas and tortillas. Commercially it is desired to have tortillas with good properties and a high yield, that is, optimum weight transformation from corn to tortilla. From our analysis, the lowest dehydration rate (lowest effective moisture diffusion coefficient) and the best physicochemical and textural characteristics of fresh masas and tortillas were obtained from flour supplemented with 0·5% (w/w) of the nonpolar lipid fraction III. The loss in starch crystallinity due to the cooking process of masa into tortilla was similar in all treatments.     

Effect of lipid incorporation on functional properties of wheat gluten based edible films

Wheat gluten is an inexpensive protein derived from mill industries with good film forming properties, which allows producing semipermeable membranes able to slow down water migration in foods.The first objective of this study was to evaluate the effects of the incorporation of a lipid phase (25 wt%, dry basis) in wheat gluten on the functional properties of the film, such water sorption, surface hydrophilicity, water barrier properties, mechanical properties and thermal properties. The second one was to asses if such incorporation was able to reduce the water sensitivity of film mechanical properties.Findings clearly showed that the incorporation of a lipid phase was able to decrease the water sorption, water affinity (hydrophilicity) and water transfer (≈2 times) of wheat gluten films. Moreover, mechanical properties are also affected by the lipid addition with a decrease in rigidity and, at high a_w, an increase in extensibility. However, the sensitivity of the mechanical properties to water was not modified. Lastly, DSC (Differential Scanning Calorimetry) analysis proved that changes in mechanical properties of films as a function of hydration state were the consequence of glass transition depletion, which allowed them to turn from a glassy-like behavior to a rubber-like behavior.     

Rapid Economic Change,the Nutrition Transition and Its Effects on the Structure of Consumption: The Nutrition Transition in China

SUMMARY

Economic, demographic, and technological changes have led to a marked shift in the diet structure and the distribution of body composition in many regions of the world. Such changes include rapid reduction in fertility and aging of the population, urbanization, epidemiological transition, and the uneven distribution of the effect of economic reform. Research presented for China shows that it is undergoing a marked shift in its diet, activity, and nutritional status patterns. This paper presents data on the shifts in the structure of food decision-making and the associated body composition shifts.     

一种观察甜菜胚囊的压片法

胚囊观察是植物胚胎学的主要研究方法之一。我们在学习了酶解法之后,摸索研究了一种观察甜菜胚囊的压片法。其步骤:固定、硼砂洋红整体染色、酸解离、剥离胚珠、透明、压片、观察。观察到了胚囊的一些情况。此法简捷易行,成本低。     

Characterisation of Glass Transition of Durum Wheat Semolina using Modulated Differential Scanning Calorimetry

The glass transition of wheat durum semolina was characterised at different moisture contents using modulated differential scanning calorimetry. The total, reversing and non-reversing heat flows were quantified during heating, cooling and re-heating. An endothermic peak was observed on the non-reversing heat flow during first heating and was not greatly affected by changes in moisture content (below 20 g water/100 g dry matter). This peak was associated with endothermic relaxation of the protein fraction in wheat semolina. An endothermic baseline shift was observed on the reversing heat flow during first heating, cooling and re-heating. The temperature at baseline shift decreased (from 110 °C to 27 °C) when moisture content increased (from 6% to 27% db). The measured heat capacity change (0·10–0·25 J/g/°C) was not significantly affected by moisture content. This endothermic baseline shift was presumed to be the glass transition of amorphous polymers in wheat durum semolina. The plasticising effect of water on the glass transition temperature (Tg) was described using Gordon Taylor and Kwei models and compared with Tg of the main wheat components.     

Glass transition temperature of starches with different amylose/amylopectin ratios

The glass transition temperatures (T_g) of starch with different amylose/amylopectin ratios were systematically studied by a high-speed DSC. The cornstarches with different amylose contents (waxy 0; maize 23, G50 50 and G80 80) were used as model materials. The high heating speed (up to 300 °C/min) allows the weak T_g of starch to be visible and the true T_g was calculated by applying linear regression to the results from different heating rates. It is confirmed for the first time, that the higher the amylose content is, the higher the T_g is for the same kind of starch. The sequence of true T_g of cornstarch is G80 > G50 > maize > waxy when samples contain the same moisture content, which corresponds to their amylose/amylopectin ratio. It was found that T_g was increased from about 52 to 60 °C with increasing amylose content from 0 to 80 for the samples containing about 13% moisture. The microstructure and phase transition were used to explain this phenomenon, in particular the multiphase transitions that occur in high-amylose starches at higher temperatures, and the gel-ball structure of gelatinized amylopectin.     

Annealing of wheat starch

The moisture, time and temperature dependence of annealing for one commercial and 10 laboratory extracted starches (from five soft and five hard wheats grown in various places in England in 1994) were investigated. Annealing was found to occur at least 15°C below the onset gelatinisation temperature (T_o), the extent of which was time dependent, but was much more evident (as indicated by the relative increase in gelatinisation temperatures) the closer to T_o the annealing temperature was set. Annealing could be initiated when the starch contained 20% by weight moisture, but the process was restricted unless the moisture content exceeded 60%. ¹³C-CP/MAS-NMR indicated that the number of double helices remained constant post-annealing and it is proposed that annealing improves the crystalline register of double helices, thereby ‘perfecting’ starch crystallites rather than promoting the formation of additional double helices. This perfection of crystallites is possibly initiated by incipient swelling and the resulting mobility of amorphous α-glucans which facilitates ordering of double helices and, probably, greater ordering of the amorphous regions themselves.     

Dielectric Relaxations of Frozen Wheat Doughs Containing Sucrose, NaCl, Ascorbic Acid and Their Mixtures

The effects of sucrose, NaCl, and ascorbic acid on dielectric relaxations of frozen wheat doughs were investigated using dielectric analysis (DEA). All ingredients were dissolved in distilled water used to prepare wheat flour doughs to optimum consistency using a 10 g bowl Micro-Mixer. DEA measurements were made at a heating rate of 1 °C/min from −150 to 10 °C. Before the measurements, samples were equilibrated at −30 °C for 15 min to allow maximum ice formation, and then cooled at 1 °C/min to −150 °C. The frequencies used were 0·1, 0·5, 1, 5, 10, 20, 50, 100 and 1000 Hz. The dissipation factor (tan δ) of DEA showed an α-relaxation (glass transition), two low temperature relaxations (β and γ) and ice dissolution. Added NaCl had a markedly depressed the glass transition temperature (T_g′) and onset of melting of ice temperature (T_m′), probably because of the higher conductivity of the frozen material, and the decreased transition temperatures of the unfrozen solute phase. At the higher frequencies, the α-relaxation coincided with melting of ice, and all relaxation temperatures (α, β and γ) increased with increasing frequencies.     

Glass transition behavior of corn distillers dried grains with solubles (DDGS)

Distillers dried grains with solubles (DDGS), a major co-product from the corn ethanol industry, has high feed value for its chemical composition. The ratio of wet distillers grains (WDG) and condensed distillers solubles (CDS) added during the production process determines the chemical composition of DDGS. Effect of changing this ratio and the influence of moisture content on glass transition behavior of DDGS was studied. Five prediction models were evaluated to explain the glass transition of DDGS. The mixed trends in the result indicated the complex behavior of DDGS particles and revealed that both moisture content and chemical composition impact the glass transition behavior of DDGS. Onset glass transition temperature ranged from 20 to 30 °C depending on the chemical composition. Kwei equation predictions were better than the predictions by Gordon-Taylor equation. The glass transition temperature of DDGS can be mathematically explained by combining the moisture content and chemical components protein, fiber, glycerol, and sugar percent. The artificial neural network (ANN) model gave a better prediction of onset and midpoint glass transition temperature of DDGS and this might be due to the accurate mapping of the interaction between chemical components.     

Water Sorption and Dielectric Relaxations of Wheat Dough (Containing Sucrose, NaCl, and their Mixtures)

Dielectric relaxations of wheat doughs with different water contents and effects of sucrose, NaCl, and their mixture on relaxation temperatures were investigated using dielectric analysis (DEA). All ingredients were dissolved in distilled water used to prepare wheat flour doughs to optimum consistency. Before analysis, samples were stored at room temperature in vacuum desiccators over a_w range of 0·225–0·753. Dynamic DEA measurements were made at a heating rate of 2 °C/min from 40 °C below and above the observed relaxation zone. The frequencies used were 0·1, 0·5, 1, and 5 Hz. Steady state water contents varied from 3·21 to 10·89 g H₂O/100 g dm over a_w range used for the plain dough (flour+water). Added ingredients increased sorption of doughs. The tan δ of DEA showed an α-relaxation (glass transition) in all doughs at all frequencies used. The relaxation peak temperature, taken as T_g, increased with increasing frequency. Added sucrose decreased the T_g of doughs, as well as added NaCl. A dramatic depressing effect of NaCl on T_g was probably due to an increase in conductivity of doughs.     

气候过渡带普文不同家系旱冬瓜育苗技术研究

[目的]为培育旱冬瓜苗木提供可靠的理论依据。[方法]选择亚热带和热带的交汇处拥有气候类型丰富多样的景洪市普文镇作为试验地,对15个种源地收集的93个旱冬瓜家系进行人工实生苗培育[结果]通过试验发现,亚热带种源地收集的种子,千粒重较大、苗木的生长情况较好;热带种源地收集的种子,千粒重较小、苗木生长情况较为缓慢。[结论]研究结果可以为良种选择、苗木培育、营造速生丰产用材林提供科学有效的依据,     

基于加权关联网络分析的辣椒(Capsicum annuum L.)果实颜色转变相关基因的鉴定

辣椒属于茄科（Solanaceae）辣椒属（Capsicum L.）一年生或多年生植物,其播种面积和产值在中国均居蔬菜首位。果色是辣椒众多经济性状中最直观的性状之一,直接影响人们的购买选择。辣椒果色受多种因素调控,相关色素生物合成的分子调控还需进一步解析。本研究以果实发育过程中呈现5种颜色的辣椒种质HNCA0076为实验材料,进行了生理检测、转录组测序以及WGCNA分析。在果实5个不同颜色时期,叶绿素含量变化较大,类胡萝卜素含量整体呈现递增趋势,类黄酮含量无明显变化,花色苷含量在紫色果期后逐渐降低,橙色果期后又逐渐升高。RNA测序数据质量满足进一步分析要求。4个转色期的上调（下调）表达基因数分别为826（276）、390（588）、1248（1800）和1528（2485）,随着果实的逐步发育,相邻比较组合中的差异基因的数量逐渐增加。差异表达基因经GO富集分析,主要集中在分子功能中的四吡咯结合、血红素结合、转移酶活性、氧化还原酶活性、铁离子结合和水解酶活性等过程;KEGG富集分析主要富集在类胡萝卜素生物合成、类黄酮生物合成和淀粉、蔗糖代谢等信号通路,其中类胡萝卜素代谢途径的3个基因在紫色时期向黄色时期的转变过程中表达上调,类黄酮代谢途径的11个基因在黄色时期向红色时期的转变过程中表达下调。4个对比组合差异基因分别注释到8877、8736、8689、8573个转录因子,共同注释到8049个转录因子,包括AP2、F-box、MYB和UDPGT等类型。利用非冗余的差异表达基因进行了加权关联网络分析,关联到4个与叶绿素、类胡萝卜素、花色苷、类黄酮含量相关的模块,进一步分析表明p450（LOC107859314）、Pkinase（LOC107839192、LOC107875415）、F-box（LOC107863894）和zf-MYND（LOC107852593）等29个转录因子可能参与辣椒果实转色的调控。本研究为进一步探索辣椒果实色素形成过程中的关键调控因子以及分析相关色素生物合成的调控提供了重要数据。     

小麦禾谷孢囊线虫病发生规律的初步研究

研究表明 ,小麦禾谷孢囊线虫病在安阳市一年发生一代。除小麦外 ,未发现危害其它植物。该病在安阳县发生普遍 ,发病田块达 78.8%。在目前推广的小麦品种中未发现高抗或免疫品种 ,但品种间抗病性有差异 ;不同轮作制度对该病的发生发展影响很大 ,采用合理的轮作方式是防治该病的有效措施之一     

Effect of Water on the Mechanical Behaviour of Extruded Flat Bread

The effect of water on the mechanical properties of extruded breads was studied, at room temperature. As the moisture content was increased from 6 to 9% moisture, the resistance to fracture (compression tests) or rupture (tensile tests) was improved. Above this moisture range, plasticisation by water was the dominant phenomenon. The brittle to ductile transition was observed to occur within a moisture content range from 9 to 13·7% (w/w). The influence of water on the crispness of extruded bread, evaluated with sensory evaluation, is also described.     

温度对马铃薯α淀粉老化的影响

采用挤压膨化技术制作马铃薯α淀粉,并利用酶水解法及X-射线衍射法等研究了在同一贮藏时间内,不同贮藏温度对膨化马铃薯α淀粉老化变化的影响,探讨了影响机理。研究结果表明,贮藏温度从23℃±1℃降低到-18℃±1℃时,贮藏期为180d的样品α度也从87.8%明显降低到80.2%,样品的结晶度从8.4%上升为16.45%;说明样品α度的高低与贮藏温度的高低成正比,而样品的老化程度高低与贮藏温度的高低成反比。     

Control of Gene Expression for the Genetic Engineering of Cereal Quality

The recent success of techniques for the direct transfer of individual genes to cereal species suggests that specific modifications to grain end-use properties will be achievable in the near future. The suitability of direct gene transfer to the problem, the choice of the promoter and transformation strategy need to be considered before attempting such modifications. This review discusses these questions with reference to current knowledge of seed-specific and, in particular, endosperm-specific and abscisic acid-responsive gene promoters. This perspective is of special importance in attempts to engineer cereal proteins.