Components of Vane Yield Stress of Structured Food Dispersions

The vane technique was used to determine the static (σ_os) and dynamic (σ_0d) yield stresses of 6 commercial foods: mayonnaise, mustard, ketchup, applesauce, and 2 brands of tomato puree (samples TD and TR). The samples, other than TR, exhibited shear‐thinning behavior. For those samples, based on a model proposed earlier, the contributions of bonding (σ‐_b), network (σ‐_n), and viscous (σ_v to yield stress of the products were determined. For the homogenized products, σ_b > σ_n, whereas for those processed in a finisher, σ_n > σ_b. Because sample TR exhibited shear‐thickening behavior, the model to estimate yield stress components was not applicable. The structural conditions necessary for the validity of the proposed model are established. Equilibrium stress (σ_∞) values obtained by extrapolation of vane torque data to infinite time were comparable to σ_0d values.     

Measurement of the Yield Stress of Protein Foams by Vane Rheometry

The yield stresses of protein foams made from varying protein types (spray dried egg white and whey protein isolate), protein concentrations, whip times, and mixer models were evaluated using vane rheometry. Two methods of analysis (point and slope methods) were investigated. Yield stress values determined by slope and point methods were similar for egg white protein foams but did not agree in the analysis of whey protein foams. Point method values were very reproducible in all foams tested. Egg white protein solutions formed stiffer foams more rapidly and at lower protein concentrations than foams made from whey protein isolate. Vane rheometry was shown to be a reliable method of determining yield stress in protein foams.     

Textural Characterization of Cheeses Using Vane Rheometry and Torsion Analysis

ABSTRACT Vane rheometry was applied to textural characterization of cheeses and compared with torsion analysis. A Haake VT 550 viscotester was used for both vane and torsion tests at strain rates of 0.003 to 0.524 s^-1. Angular deformation and shear stress in the vane test increased with increasing low strain rate and was rate independent at higher rates. This shear rate dependency of stress and deformation varied with cheese types. Shear stresses from the vane method were lower than torsion shear stresses. Similar texture maps of cheeses were generated by plotting stress and strain or angular deformation values from the 2 testing methods. The findings indicate the vane technique can be used for rapid textural characterization of cheeses.     

Centrifugal Slump Test to Measure Yield Stress

ABSTRACT: The performance of a centrifugal viscometer (a new concept) was tested for its ability to accurately predict the yield stresses of semisolid foodstuffs. This instrument is based on the traditional slump test concept, but utilizes centrifugal force rather than gravitational force to cause deformation. Using dimensional analysis, there was a general agreement between the theoretical approximation of the yield stress, and experimental data generated using the vane method.     

抗性淀粉产率的影响因素研究

本文综述了影响抗性淀粉产率的各种因素，包括淀粉的性质、淀粉与其它成分的相互作用、加工条件、储存条件以及其它因素的影响。     

Rheological Properties of Rice Starch Dispersions in Dimethyl Sulfoxide

The steady and dynamic shear rheological properties of rice starches dispersed in dimethyl sulfoxide (DMSO) solution (90% DMSO‐10% water) were evaluated at various concentrations (7, 8, 9 and 10%, w/w). Rice starch dispersions in DMSO solution at 25°C showed a shear‐thinning flow behavior (n=0.44–0.60) and their consistency index (K) and apparent viscosity (η_a,100) increased with the increase in concentration. The apparent viscosity over the temperature range of 25–70°C obeyed the Arrhenius temperature relationship, indicating that the magnitudes of activation energy (E_a) were in the range of 11.7–12.7 kJ/mol. The Carreau model provided better fit on the shear rate‐apparent viscosity data than the Cross model. Dynamic frequency sweep test showed that both storage modulus (G′) and loss modulus (G′′) of rice starch dispersions increased with the increase in concentration. G′′ showed a higher dependence on frequency (ω) compared to G′ due to the higher G′′ slopes. All rice starch dispersions showed the plateau of G′ at high frequencies. Intrinsic viscosity of rice starch dispersions in DMSO was 104.1 mL/g.     

淀粉平均聚合度对抗性淀粉得率影响的研究

在对普鲁兰酶最佳酶解条件优化的基础上,采用普鲁兰酶与耐高温淀粉酶协同制备RS(resistantstarch),改变淀粉的聚合度,分析玉米淀粉聚合度与抗性淀粉得率的关系。结果表明:提高原料淀粉中直链淀粉含量并将其聚合度控制在一定程度,可有效的提高RS得率,同时,DSC(differentialscanningcalorimeter)和X-衍射图谱表明,抗性淀粉与原玉米淀粉在结构上有着显著差异。     

浆浓及助留助滤剂对桉木浆纤维悬浮液屈服应力的影响

纸浆纤维悬浮液的屈服应力（τy）是纸浆流体力学的关键流变参数。研究了桉木漂白硫酸盐浆（BKP）的浆浓（Cm）以及分别添加阳离子聚丙烯酰胺（CPAM）和阳离子淀粉对其纤维悬浮液屈服应力的影响。结果表明,在稳态剪切条件下,桉木BKP纤维悬浮液屈服应力随浆浓的升高而迅速增大,两者符合指数关系,即τy=aCbm（a=3.20,b=2.62）;添加CPAM或阳离子淀粉后,两者仍满足该指数关系,但添加CPAM后,a值减小、b值增大,而添加阳离子淀粉后,a和b值均在原来的基础上上下浮动。浆浓一定的桉木BKP,其屈服应力随CPAM添加量的增加,先增大后减小,但仍大于不添加CPAM桉木BKP纤维悬浮液的屈服应力;当浆浓为4.0%、添加约0.6%（相对于绝干浆质量,下同）的CPAM时,其屈服应力增幅最多,达30%;随着阳离子淀粉添加量的增加,屈服应力先增大后减小,当添加约为2.5%的阳离子淀粉、浆浓4.0%时,桉木BKP纤维悬浮液屈服应力下降最多,降低了约25.4%。     

Rheology and Relationship among Rheological Parameters of Cross-Linked Waxy Maize Starch Dispersions Heated in Fructose Solutions

ABSTRACT: Dispersions of 5% cross‐linked waxy maize starch heated in Newtonian aqueous fructose solutions, 0 to 600 g per kg, exhibited either thixotropic or antithixotropic flow behavior, and viscoelastic behavior. The mean starch granule dia in the dispersions changed slightly with fructose content. Values of G' of the dispersions were higher than those of G', reflecting gel‐like behavior of the dispersions. Values of the first normal stress coefficient predicted from dynamic rheological and apparent viscosity data based on the Goddard‐Miller model were in reasonable agreement with experimental values.     

Starch source and content in postpartum dairy cow diets: effects on plasma metabolites and reproductive processes

The objective of this study was to examine the effects of dietary starch source and content in the immediate postpartum period on plasma metabolites and hormones and ovarian follicular development. One of 3 diets was fed in a randomized block design to 40 cows from calving until 70 d in milk. The diets contained 45% alfalfa silage (AS), 45% barley silage (BS), or 41% barley silage and 4% supplemental starch (SS) on a dry matter basis. All diets contained 45% barley-based concentrate and 10% alfalfa hay. Resulting starch levels were 25.2, 23.3, and 26.7% for AS, BS, and SS, respectively. Body condition was scored every other week and dry matter intake and milk yield were recorded daily. Milk samples were obtained weekly and blood samples were taken at calving and then every other week to determine concentrations of glucose, insulin, insulin-like growth factor-1, β-hydroxybutyrate, and nonesterified fatty acids. Transrectal ultrasonography was performed twice per week from 7 d after calving until first ovulation or 62 d in milk in all cows. For a subset of 7 AS-, 8 BS-, and 9 SS-fed cows, a complete estrous cycle was monitored for ovarian dynamics, and blood samples were collected every second day for progesterone and estradiol. Luteinizing hormone pulsatility was also determined (5 cows/treatment) approximately 15 d postcalving. Treatment had no effect on body condition score, dry matter intake, blood metabolites, milk yield, or milk fat and protein contents, but BS-fed cows had significantly higher levels of milk urea nitrogen compared with SS cows. Cows fed SS (31 d) tended to have a shorter interval from calving to first ovulation than cows fed AS (43 d) or BS (38 d). The incidence of double first ovulations was higher in cows fed SS (46%) compared with those fed BS (0%). Treatment had no effect on LH pulse frequency or amplitude, ovarian dynamics, or progesterone and estradiol concentrations during the observed estrous cycle. Energy balance did not differ among cows fed the 3 diets. Overall, dietary starch source and concentration had little effect on productivity or metabolic status of postpartum cows.     

玉米淀粉实验室提取方法研究

以普通黄马齿玉米为原料,采用湿法提取淀粉工艺,制得淀粉得率高、优质纯净玉米淀粉;通过大量实验设计筛选出最佳提取方案:浸泡温度50℃,乳酸和NaHSO3浓度均为0．5％,浸泡时间36 h,流槽倾斜度为0．015 cm／cm。     

水肥耦合对小麦产量及淀粉特性的影响

利用干旱棚,以洛阳1971～1999年20年的降雨量为依据,以每月占年平均降雨量的加权值进行分配,模拟不同水肥条件下对小麦产量及淀粉特性的影响.结果表明:不同降雨年型不同施肥组合有以下规律:N、P水平相同的情况下,水分高的处理产量高;在欠水年和丰水年,P肥相同的情况下,N肥高的产量低;在平水年,不同施肥水平呈现出不同变化,氮肥N105＞N0＞N210,氮肥相同水平下P84 ＞P168 ＞P0.水分是产量的主导因素.小麦产量的提高可通过协调成产3因素来实现.淀粉的峰值黏度、终结黏度、稀懈值及反弹值受水肥影响较大,而糊化温度和低谷黏度受水肥影响较小,在平水年以N105P84处理的淀粉糊化特性各参数值较高,在一定程度上改善了面条品质,而在丰水年氮肥较高的各参数的值较低.     

3种玉米淀粉的性质比较

研究了高直链玉米淀粉、糯玉米淀粉、普通玉米淀粉的粒度分布、糊流变、质构、冻融稳定性等物理化学性质,结果表明:3种玉米淀粉的颗粒形状差异不大。高直链玉米淀粉的粒度分布一致性较高,同样条件下糯玉米淀粉糊粘度大于其他2种淀粉,糯玉米淀粉的冻融稳定性大于普通玉米淀粉和高直链玉米淀粉,为玉米淀粉在食品中的应用奠定了基础。     

Vane Rheometry for Textural Characterization of Cheddar Cheeses: Correlation with Other Instrumental and Sensory Measurements

The relationship between instrumental (vane method, texture profile analysis (TPA), uniaxial compression) and sensory texture measurements of Cheddar cheeses was investigated. A Haake VT 550 viscotester equipped with a four-bladed vane rotor was used for the vane test. Instrumental TPA was performed with a TA.XT2 Texture Analyser, and compression variables were calculated from TPA data. Vane parameters were significantly correlated with respective variables of compression and TPA (r=0.56-0.91), and sensory tests (r=0.54-0.88). Multivariate analysis indicated that seven sensory attributes of ten commercial Cheddar cheeses were satisfactorily predicted (calibration regression coefficient,R_cal >0.62) by variables of the vane, uniaxial compression and TPA tests. In particular, cheese firmness and cohesiveness evaluated by sensory panel were well described by vane stress and apparent strain. The results validate the vane method as an alternative to the existing cheese testing methods for rapid evaluation of cheese texture.     

马铃薯淀粉糊在超声场中凝胶质构特性的变化研究

淀粉糊凝胶特性对食品加工过程有重要指导作用。本实验以马铃薯淀粉糊为研究对象,考察在超声场中,不同超声场条件、不同马铃薯淀粉糊浓度下,马铃薯淀粉凝胶强度的变化规律。结果表明:超声场中马铃薯淀粉凝胶质构分析性质(TPA性质)显著改变,延长超声场作用时间和增加声强会降低凝胶的硬度值、脆度值、粘性值、胶粘性值和耐咀性值。随着马铃薯淀粉糊浓度增大,超声场中马铃薯淀粉糊凝胶的硬度值、胶粘性值和耐咀性值下降趋势变小。     

Yield Stress and Time-dependent Rheological Properties of Mango Pulp

Mango pulp was tested for time-independent and time-dependent flow properties using a coaxial cylinder rheometer. Mango pulp is a pseudoplastic liquid with yield stress, and exhibits thixotropic properties. The yield stress calculated using the Casson or Bingham plastic models, had markedly higher values than those determined by stress relaxation, controlled stress experiments, or from stress-strain plots. The yield stress of mango pulp tested in this experiment was sensitive to temperature and decreased rapidly as temperature increased. The time-dependent model of Weltman was found to be most applicable (|r| 0.991, p 0.01) for mango pulp.     

磷酸酯改性淀粉的制备及在肉类中的应用

以糯玉米淀粉为原料,采用复合磷酸盐进行酯化,以取代度为指标,分别考察了pH、正磷酸盐添加量、磷酸盐配比、反应温度、反应时间对酯化的影响,并对其进行了优化,得到最佳工艺条件:糯玉米淀粉乳浓度40%,反应pH=5.5,正磷酸盐添加量37.5g,磷酸二氢钠与磷酸氢二钠的配比0.4,反应温度150℃,反应时间2h。将磷酸酯淀粉添加在火腿肠中时,其弹性、粘聚性、胶着性、咀嚼度等明显优于添加原淀粉的产品,其中取代度为0.1257,添加8%时最佳。     

Texture Map of Cream Cheese

ABSTRACT: The controlled rate vane method was used to evaluate the yield stress and apparent yield strain of ten cream cheeses at refrigeration (5 °C) and room temperature (22 °C). Plotting yield stress versus apparent yield strain produced a "texture map", showing a trend where a decrease in yield stress corresponded to an increase in yield strain. The map can be used as a tool for evaluating product spreadability in quality control and product development applications. Yield stress values for all cream cheeses ranged from approximately 1.3 kPa to 6.6 kPa, while yield strain values from 0.2 rad to 0.6 rad were found.     

Factors Determining Yield Stress and Overrun of Whey Protein Foams

ABSTRACT: Foams were formed by whipping whey protein solutions (15% w/v protein) containing NaCl, CaCl₂, lactose, or glycine. Foam overrun and yield stress were determined. Foams made from whey protein ingredients have greater overrun and yield stress if the concentration of β-lactoglobulin is high relative to a-lactalbumin. The presence of 0.4 M CaCl₂ in the foaming solution increases overrun and yield stress for β-lactoglobulin and a-lactalbumin. The high yield stress of β-lactoglobulin and a-lactalbumin foams made from solutions containing CaCl₂ suggests that CaCl₂ is altering rheological properties of the interfacial protein film and/or contributing to protein aggregation or network formation in the lamellae.     

大米淀粉结构与质构品质的研究进展

随着人民生活水平的改善,对大米口感品质的期望越来越高,其中大米的硬度和黏度品质是众多口感品质中最具识别性的两种,可通过质构仪进行表征。本文详细探讨影响大米质构品质的主要因素,介绍测定大米质构品质常用的方法以及发展趋势。由于淀粉是大米最主要的组分,因此还综述了淀粉的多层级结构及其表征方法,并重点总结大米主要质构品质(硬度和黏度)的分子机制,即淀粉结构与大米质构品质的构效关系,以期为大米口感品质的改善与美味米制食品的开发提供借鉴。