The effect of processing temperatures on the quality of labneh made by ultrafiltration

Twelve batches of labneh were manufactured by using the traditional method and also by ultrafiltration (UF) of yogurt at temperatures ranging from 35°-55° C. The labneh samples contained 21.3–26.4% total solids (including minerals and unmetabolized lactose), 6.6–9.3% protein and 9.8–12.6% fat. The highest flux rate during UF was observed at temperatures 50° C, but the total viable counts of the starter organisms were lower when compared with labneh concentrated at 45° C. Portions of each of the labneh samples were smoothed using a lactic curd homogenizer fitted with different homogenizer heads (D-170 and D-280). Homogenization markedly affected the firmness of labneh and is therefore recommended to smooth the product using homogenizer head D-280 because it causes less turbulence.     

Effect of Carob Flour Addition on the Rheological Properties of Gluten-Free Breads

In this study, the rheological properties of gluten-free doughs from rice flour containing different amounts of carob flour were investigated. Water added changed in response to the carob amount. Dynamic oscillatory and creep tests were performed in order to gain knowledge on the rheological behaviour of doughs, which is essential for the control of the bread-making procedure and the production of high-quality bread. Simple power law mathematical models were developed in order to evaluate the effect of carob and water added in dough rheological behaviour. Creep data evaluation demonstrates that an increase in water content decreased the resistance of dough to deformation and, therefore, dough strength, whereas carob flour increased the elastic character and structure strength of the dough. This was also found in dynamic oscillatory tests. Increased amounts of carob flour led to an increase in bread dough elastic character since fibre addition elastifies and strengthens the dough structure. Moreover, doughs exhibited a solid-like viscoelastic character, with the storage modulus (G′) predominant over the loss modulus (G″). Dough rheological properties have an important effect on baking characteristics. Rheological experiments and applied mathematical models can provide us with good knowledge of rheological behaviour and dough viscoelasticity prediction. Therefore, dough samples containing carob-to-water ratios of 10:110 and 15:130 can be considered to possess a balance between the viscous and elastic properties compared to the other samples.     

Rheological behaviour of β-glucan preparations from oat products

The cereal dietary fibre β-glucan has outstanding functional and nutritional properties, because of its viscosity in aqueous systems and in the intestinal tract. The rheological behaviour of β-glucan (concentrations: 2% and 4%) isolated from extruded and autoclaved oat meal and from oat bran was evaluated using oscillatory and rheological measurements. In frequency sweep, the storage and loss moduli G′ and G″ of β-glucan preparations from extruded meal and from bran increased continuously with increasing frequency, showing a dominantly viscous behaviour. With increasing frequency, the elastic properties improved. β-Glucan from autoclaved meal also showed elastic behaviour. With the exception of β-glucan from autoclaved meal, G′ and G″ were not influenced by deformation in the amplitude sweep. Complex viscosities decreased with frequency (in all samples) and were independent of deformation (in extruded meal and bran). In shear experiments, β-glucan solutions were structurally viscous non-Newtonian solutions with rheostable behaviour. β-Glucan (2%) from bran had the highest and that from autoclaved meal had the lowest apparent and process viscosities. Fluid dynamic parameters may influence the flow, diffusion or transport behaviour of β-glucan during digestion processes in the small intestine, but the influence of the viscous behaviour is limited.     

Validation of a large amplitude oscillatory shear protocol

Oscillatory shear rheology plays a valuable role in assessing rheological properties of viscoelastic materials. In the linear viscoelastic region (LVR), the stress response to a strain input comprises only the first harmonic. Beyond the LVR, higher-order harmonics have significant contributions, which are not accounted for in the traditional calculation of viscoelastic moduli. Previous study has developed a mathematical framework that accounted for higher-order harmonics during large amplitude oscillatory shear (LAOS), yielding a physical interpretation to nonlinear data. However, this protocol was not formally validated with model elastic and viscous systems. To that end, a model elastic solid and viscous liquid were tested using LAOS to compare the protocol to standard oscillatory data and the known nonlinear properties of both systems. Good agreement (α = 0.05) was shown between first-order harmonic viscoelastic moduli data for both systems in the linear region. The protocol correctly indicated linear-to-nonlinear transitions of the elastic system, strain-independent linear behavior of the viscous system, and strain-hardening behavior of the elastic system in the nonlinear region. These results indicate the validity of the protocol, which may be applied to food systems to give valuable insights into nonlinear behavior and elucidate structural keys to texture design.     

菊粉对Labneh浓缩酸乳微观结构和质构的影响

研究了添加菊粉对脱脂乳制备的Labneh(一种浓缩酸乳)物理和感官性质的影响。将市售菊粉按不同比例( 1%、3%、5 %和7% )加入至复配脱脂乳粉(reconstitutedskimmilkpowder,RSMP)制作Labneh样品。通过对酸乳宏观和微观结构的分析发现,添加菊粉后,Labneh凝胶结构和凝胶强度都有所改善。实验表明,与未加菊粉的酸乳相比,含有脂肪替代品的酸乳的微观结构比较均匀、疏松且开放度较高。感官评定的结果表明,5 %菊粉复配脱脂乳粉制作的酸乳与全脂牛乳制作的Labneh相比具有相似的特征,对全脂牛乳制作的样品和添加3%、5 %、7%菊粉的样品的统计分析结果没有显著的差别     

Effect of protein concentration on the properties and structure of concentrated yogurts

Concentrated yogurts were produced by traditional (control), direct reconstitution, ultrafiltration and reverse osmosis techniques. The membrane techniques were applied either before or soon after incubation. The physical properties of the samples were monitored using a penetrometer (set yogurt) and viscometer (stirred yogurt), and the results indicated that different manufacturing techniques led to differences in the rheology of the concentrated yogurts. As expected, samples with high protein contents had greater gel strengths. Also, the concentration techniques caused large differences between the samples, even at the same protein level. The rheological properties correlated well with the microstructure as monitored by confocal laser scanning microscopy. In general, larger compartments in the network were associated with a weaker structure.     

Viscoelastic Properties of Tomato Juice: Applicability of the Cox–Merz Rule

Tomato is one of the most important vegetables for the food industry. Rheological characterization of food is important for products, equipments, and unit operations design and evaluation. It is necessary for process optimization and high-quality products assurance. However, the works in literature present variable data, and some rheological characterization, as viscoelastic properties, are still scarce. The present work has evaluated the viscoelastic properties of tomato juice, as well as the applicability of the Cox–Merz rule. Tomato juice has shown dominant elastic properties rather than the viscous ones and could be classified as a weak gel (storage modulus higher then loss modulus). Moreover, due to the low pulp content, it has shown low viscoelastic behavior, with small dependency of oscillatory of the storage modulus. The rheological oscillatory and steady-state shear rheological properties of tomato juice were then correlated by two linear modifications on the Cox–Merz rule. The obtained values are in agreement with those described in the literature for other food products. The obtained data are potentially useful for future studies on food properties and process design.     

Bread crumb quality assessment: a plural physical approach

The aim of this study was the assessment of pan bread crumb quality attributes of commercial samples using a plural physical approach to better match consumer awareness. Static (texture profile analysis, firmness AACC and relaxation test) and dynamic (innovative oscillatory test) deformation techniques, image analysis, sensory analysis and colour measurements (colorimeter and Photoshop system) were used for white/whole commercial pan bread quality evaluation over 10 days of storage. Static (k ₁, k ₂, cohesiveness, springiness, hardness, chewiness and resilience) and dynamic (stress) bread crumb rheological properties were correlated illustrating that both techniques can be useful in evaluating crumb physical characteristics. In addition, sensory perceiveness with regard to softness and overall acceptability exhibited dependence with either dynamic stress or static firmness. Despite the fact that empirical measurements are closely linked to macroscopic features whilst dynamic tests are strongly linked to molecular characteristics, the obtained results support that both techniques are complementary since derived instrumental parameters are related to some sensory attributes. As data achieved using the proposed novel approaches might be better linked to the consumer awareness than those obtained from classical analyses, the obtained results are promising for a proper bread crumb quality assessment.     

Structural parameters that determine the rheological properties of apple puree

The objective of this work is to better understand how the structural parameters (particle content, particle size and serum viscosity) influence the rheological properties of apple purees. An apple puree (called “native”) was ground to obtain dispersions with three different particle size distributions. This mechanical treatment induced the separation of parenchyma irregular cell clusters into regular single cells, modifying both the morphology and the particle size distribution of purees. A separation–reconstitution step made it possible to obtain samples with a wide range of insoluble solids (8–24 g/kg). Pectin was added to some of the samples in order to increase the viscosity of the continuous phase. The rheological behaviour and structural properties of the modified apple purees were investigated using flow and oscillatory rheological measurements, particle size measurements and confocal laser scanning microscopy. Rheological properties such as apparent viscosity, yield stress and elastic modulus decreased as particle size decreased and they increased as insoluble solids content increased. Modelling of rheological properties with master curves made it possible to take into account the apparent relative volume occupied by the particles of different sizes.     

Wafer batters: A rheological study

The performance of single wheat varieties in the production of wafer batters at a constant solids content has been studied. Following a standard mixing procedure dynamic oscillatory measurements were performed to obtain the phase angle and the elastic and viscous moduli. The effect of shear rate on batter viscosity was monitored as a function of increasing shear rate. Batters were centrifuged to obtain batter liquor, the liquid fraction of the batter mix, and its surface properties characterized. Surface tension values were measured and the surface rheology of the films formed at the air-batter liquor interface determined using an oscillating ring surface shear rheometer. Compositional information of the batter liquor phase has been obtained using thin layer and gas chromatography. There was no direct relationship between the surface properties of the batter liquor and standard tests of wafer batter performance. Hard milling wheat varieties produced batters with stronger rheological properties than soft milling varieties. The bulk elastic moduli of the batters were correlated with the hydration of gluten proteins. The dispersion of gluten proteins was found to be dependent upon the phase angle of the batter. Low phase angle values, ie greater dominance of elastic properties, led to increased gluten dispersion times and potential difficulties in production.     

超声及酶解处理的罗望子木葡聚糖流变特性研究

研究了超声处理1.5和2.5 h和半乳糖苷酶酶解16、32和48 h对罗望子木葡聚糖（Xyloglucan,XG）流变特性的影响。使用旋转流变仪对处理前后的木葡聚糖在静态剪切和动态剪切下的黏度和模量进行了分析,并利用凝胶色谱-多角度激光光散射和动态激光光散射仪对木葡聚糖分子量分布和平均粒径进行了分析,同时使用扫描电子显微镜对木葡聚糖的微观结构进行了观察。温度扫描结果表明,在5 ℃时,超声和酶解处理过的木葡聚糖的黏度显著降低（P<0.05）,但不同处理时间的样品差异较小。在5~60 ℃范围内,木葡聚糖的弹性模量与黏性模量均接近于7 Pa。超声处理的样品黏度随温度增加而降低,且总体呈现出以黏性为主的流变特性。48 h酶解处理的木葡聚糖弹性特征高于16及32 h酶解木葡聚糖的弹性特性。分子量分析结果显示,超声处理1.5和2.5 h的木葡聚糖平均分子量从原885 kDa分别降低至780和520 kDa;而酶解的木葡聚糖由低分子量（101~478 kDa）和高分子量（4591~12173 kDa）两部分组成,其中低分子量组分比例占80%以上。动态光散射结果表明,经半乳糖苷酶酶解的木葡聚糖平均粒径增大,而超声对样品的粒径影响较小。本研究为物理及生物法改性木葡聚糖,以获得具有不同流变特性的多糖胶体提供了一定经验,有利于进一步拓展其在食品工业中的应用。     

EFFECTS OF INTERMOLECULAR INTERACTIONS AND MOLECULAR ORIENTATION ON THE FLUX BEHAVIOR OF XANTHAN GUM SOLUTIONS DURING ULTRAFILTRATION

Conformational changes of xanthan gum as a function of concentration were investigated to elucidate its unusual flux behavior during ultrafiltration (UF). The contribution of hydrogen bonding on structure formation and the molecular orientation of xanthan gum on the flow characteristics were studied rheomechanically and rheo-optically. Known to affect xanthan structure at low concentrations, hydrogen bonding unexpectedly did not show significant influence on xanthan rheological properties up to 2 wt %. The ordered layers formed on the membrane surface proved responsible for the enhanced water removal during UF. This unique behavior could be attributed to the formation of aligned molecular orientation in addition to the viscosity increases during the biphasic region. Significant differences were observed between xanthan fermentation broth and solutions made of commercial xanthan, suggesting the need to control the salt concentration in fermentation broth in order to make UF an effective recovery process for xanthan gum after fermentation.

PRACTICAL APPLICATIONS

The knowledge gained from the present study strengthens fundamental understandings on the conformational changes of xanthan biopolymers during the recovery of xanthan gum from fermentation broth using ultrafiltration (UF). By taking advantage of the aligned molecular orientation, along with controlling the salt concentration in the fermentation broth, UF could be operated at elevated flux to speed up the removal of water from the viscous fermentation broth. The technology should find broad applications in the fermentation industry, especially where viscosity is of concern during the separation and purification of the product.     

褐藻胶对蛋黄酱流变特性的影响

探讨了改善蛋黄酱品质的最佳褐藻胶添加量,利用流变仪研究了不同添加量的褐藻胶对蛋黄酱流变特性的影响.静态流变特性的研究表明:蛋黄酱样品呈现出触变性、假塑性,流变学方程为Herschel - Bulkley;温度对蛋黄酱样品的表观粘度的影响符合Arrhenius模型.动态流变性质的研究表明:蛋黄酱样品显示弱凝胶的特性.实验表明:添加褐藻胶的能显著提高蛋黄酱的流变学稳定性,其中褐藻胶添加质量分数为2.0％的蛋黄酱样品比添加量为2.5％的蛋黄酱样品在流变学特性、感官特性上更接近全脂类蛋黄酱.     

Non-linear viscoelasticity modeling of tomato paste products

This paper deals with the characterization and modeling of the non-linear rheological properties of tomato paste samples manufactured under different conditions (sieve pore size and breaking temperature). With this aim, flow measurements, dynamic linear viscoelastic and linear and non-linear stress relaxation tests have been carried out on the above-mentioned tomato paste samples. Different geometries with smooth and serrated surfaces have been used to optimize the viscous flow measurements and avoid wall-depletion phenomena. The viscous flow properties of tomato paste samples depend on water insoluble solids (WIS) content and particle size, which may be highly influenced by processing conditions. In general, viscosity follows a power-law relationship with tomato paste water insoluble content and particle diameter. A factorable non-linear viscoelasticity model, the Wagner integral equation, predicts the non-linear rheological response of these products under shear fairly well. The time-dependent part of this model is described by a continuous linear relaxation spectrum, calculated from regularization techniques. The use of the Soskey–Winter damping function provides the best predictions of the viscous flow curves.     

Rheological properties of ice cream mixes and frozen ice creams containing fat and fat replacers

Ice cream mixes and frozen ice creams at milk fat levels of 12%, 8%, 6%, 6% plus a protein-based fat replacer, and 6% plus a carbohydrate-based fat replacer were evaluated for viscoelastic properties by dynamic testing with sinusoidal oscillatory tests at various frequencies. The storage modulus (G'), loss modulus (G"), and tan delta (G"/G') were calculated for all the treatments to determine changes in the viscous and elastic properties of the mixes and frozen ice creams due to fat content. In ice cream mixes, G' and G" exhibited a strong frequency dependence. The G" was higher than G' throughout the frequency range (1 to 8 Hz) examined, without any crossover, except for the 12% mix. Elastic properties of the ice cream mixes decreased as fat content decreased. Tan delta values indicated that fat replacers did not enhance the elastic properties of the ice cream mixes. In all frozen ice creams, G' and G" again showed a frequency dependence throughout the range tested (0.5 to 10 Hz). The amount of fat in ice creams and the degree of fat destabilization affected the elasticity in the frozen product. Even though the ice creams did not have significant elastic properties, when compared as a group the samples with higher fat content had higher elastic properties. The addition of protein-based and carbohydrate-based fat replacers did not enhance the elastic properties of the ice creams but did increase the viscous properties.     

RHEOLOGICAL PROPERTIES OF AGED ASEPTIC ICE CREAM MIX AND MELT1

Age thickening of UHT steam injected ice cream mix and melt was investigated by determining rheological model constants. By utilizing a cone and plate viscometer, rheological models (3 element solid) were developed for creep-relaxation. Empirical relationships were derived relating the elastic and viscous constants to storage time. Soft serve ice cream mix (4.0% fat) was processed at 149°C for 3.4, 6.9, and 20.3 s. The ice cream mix was stored at 20 and 30°C and tested at four week intervals from zero through 24 weeks. Flow properties of the mixes and melts were quite stable throughout the storage period although the lowest heat treatment (3.4 s for 149°C) suggested mild age thickening by 24 weeks. The strongest element constant for all samples was the series elastic. The viscous constant was next with the Kelvin elastic constant being quite weak. Melts had lower constants than the mixes. Model constants varied little between samples stored at 20°C and those at 30°C.     

湿热处理对大米淀粉流变特性的影响

本文通过测定湿热处理前后大米淀粉的流变学特性,旨在研究湿热处理对大米淀粉稳态流变、动态流变及温度流变学行为的变化.结果表明,湿热处理后大米淀粉均呈现剪切稀化的现象,且湿热处理增强了大米淀粉的凝胶强度;在动态流变测定中发现,所有大米淀粉样品的弹性模量(G′)都大于黏性模量(G〃),且湿热处理后大米淀粉的弹性模量(G′)和...     

RHEOLOGICAL PROPERTIES OF CONCENTRATED YOGHURT (LABNEH)

The effect of six techniques for the elevation of the total solids on the rheological properties of labneh were investigated using controlled-stress dynamic rheometer. All samples exhibited a weak viscoelastic gel structure with the storage modulus (G') higher than the loss modulus (G") over all of the measured range. None of the experimental materials produced the same overall gel strength as the control made by draining with traditional cloth-bags. The changes in the storage modulus (G') as a function of amplitude sweep were mirrored by changes in the loss modulus (G"). Considerable differences in the loss tangent (G"/G') values of the various materials were observed at higher stress amplitudes. Rheological differences in the overall gel strength at low amplitude and frequency suggest that, although the type of protein interactions in each case may be similar, there are differences in the degree of interactions. Subsequent breakdown at higher amplitudes and frequencies suggests that the overall domains of the treated proteins may have been reduced, and that different methods of manufacture may be producing materials that have different space occupancy in the gel.     

Effects of massaging time on texture, rheological properties, and structure of three pork ham muscles

Changes in texture parameters (hardness, cohesiveness, chewiness), rheological properties (elastic and viscous moduli), and structural elements (fibre cross-sectional area and thickness of peri- and endomysium) of three pork ham muscles: Biceps femoris (BF), Semimembranosus (SM), and Quadriceps femoris (QM), subjected to effective massaging for 2, 4, 6, 8, 10, 12 h were followed. BF, with its higher fibre cross-sectional area thicker peri- and endomysium, compared with QF and SM, was harder, more elastic, and more viscous than the other two muscles. Massaging resulted in an increase in the mean fibre cross-sectional area, changes in thickness of the peri- and endomysium, and a reduction in hardness and chewiness as well as in elastic and viscous moduli of the muscles studied. The lower were the initial values of textural and structural parameters and rheological properties of a muscle, the shorter massage time was necessary. To arrive at comparable values of textural parameters, rheological properties, and a similar sensory acceptance, BF, SM, and QF had to be effectively massaged for 12, 6, and 4 h, respectively.     

Evaluation of rheological and textural properties of texture-modified rice porridge using tapioca and sago starch as thickener

Texture modification of food is one of the strategies to manage people with dysphagia. It is commonly done by addition of thickener to achieve the desired texture for people with dysphagia which aids in reducing the risk of aspiration. In this study, the effects of different thickeners (tapioca starch, sago starch and commercial thickener) at different concentrations (1–3% of total weight of ingredients) on rheological and textural properties of rice porridge were evaluated. The flow behaviors of samples were determined based on the rheological parameters of Power law and Casson model. All samples showed shear thinning behavior (exhibited by flow behavior index, n, <1) with yield stress. The dynamic moduli (G′ and G″) and tan\(\delta\) values from oscillatory frequency sweep test indicated that all samples exhibited more elastic behavior except for control and sample of rice porridge with the addition of low concentration (1%) of commercial thickener. Textural parameters of thickened rice porridge, analyzed using back extrusion test were found to be increased with increased its concentration of the thickener used. Overall, sago starch shown to have greater potential to be used as an alternative thickener compared to tapioca starch as it provides higher viscosity and more elastic behavior in rice porridge.