Effect of processing on rheological,structural and sensory properties of apple puree

The relation between rheological, structural and sensory properties of apple purees was studied taking into account the effect of processing. For this reason, a grinding - separation strategy was established in order to vary pulp content and particle size. By grinding, three different particle size distributions were obtained. A second heat treatment was applied to purees to see the impact on its rheological and structural properties. An experimental design was constructed, with two factors (pulp content and particle size) and 4 levels (25, 31, 42, 60%) for pulp content and 3 levels (200, 500, 1100 μm) for particle size. The rheological properties of purees were characterized using a controlled stress rheometer by the flow curves obtained from 2.14 to 214 ^s−1 shear rate range; frequency sweeps measurements were performed within the linear viscoelastic region, in the range of 0.1-40 rad/s. Purees behaved as shear-thinning fluids presenting a yield stress. Apparent viscosity and yield stress increased as pulp content increased, and they decreased as particle size decreased. The least shear thinning behaviour was observed in purees with low pulp content and small particles. A second heat treatment affected cell wall structure inducing a decrease of the rheological properties of the puree. The most important attributes to explain the texture of apple purees are consistency and graininess, parameters that can be manipulated by controlling processing conditions.     

Instrumental and sensory characterisation of industrially processed applesauces

BACKGROUND: In the context of fruit consumption promotion, applesauce is an interesting ready‐to‐eat product. However, little information has been gathered on its sensory properties. Yet, the processing involved easily triggers rheological and structural changes, possibly modifying these sensory properties. The aim of this study was thus to provide a global approach for applesauce characterisation by studying instrumental and sensory properties, with knowledge of the processing conditions applied. Four applesauce samples processed under controlled parameters were therefore compared with seven purchased applesauces. RESULTS: The four studied samples were characterised by their high creaminess and low graininess. These products were homogeneous and presented a small average particle size (332–354 µm). Their flow properties were best described with the Hershel–Bulkey model. The products were shear‐thinning with low yield stress. Interestingly, significant differences in textural and flow properties were also found among these four manufactured samples. CONCLUSION: Sensory characterisation revealed aromatic and textural diversity even though applesauce is considered as a common product. Differences found among the samples of interest might be related to postharvest maturity of fruits and consequent pectic degradation from cell walls. Finally, the candied odour and flavour that distinguished these products could be related to the extensive heating applied during processing. Copyright © 2009 Society of Chemical Industry     

Relation Between Particle Properties and Rheological Characteristics of Carrot-derived Suspensions

The effect of particle properties on the rheological behaviour of carrot-derived suspensions was investigated systematically. Hereto, a range of relatively monodisperse suspensions, with varying average particle sizes (～73, 176, 262 and 369 μm) and pulp contents (from 30 to 65 wt.%), was prepared by the reconstitution of carrot tissue particles in water. Suspensions with average particle size of ～73 μm consisted of cell fragments, whereas suspensions with larger particle sizes contained mainly cell clusters of which the cell number increased with increasing particle size. The rheological characteristics showed that the carrot-derived suspensions have a non-Newtonian behaviour with a yield stress, depending on particle concentration, size and type. The network structure of all suspensions could be described as a weak gel. Increase in yield stress and storage modulus with particle concentration could be fitted to a power law model. A unique linear relation was found between the yield stress and the plateau modulus, independent of the particle size and type. Particle concentration, size and type appeared to be key structural parameters controlling the rheology of these carrot-derived suspensions. When comparing the rheological behaviour of the reconstituted suspensions with the original carrot purée of similar average diameter and pulp content, the network structure (measured as yield stress or storage modulus) in carrot purée was weaker, which may be attributed to the broader particle size distribution.     

EFFECT OF UNIMODAL PARTICLE SIZE AND PULP CONTENT ON RHEOLOGICAL PROPERTIES OF TOMATO PUREE

The vane method in controlled shear stress mode was used to determine the yield stress and the shear rate—shear stress data of tomato purees containing 10–35% pulp of two different average particle sizes: 0.34 and 0.71 mm. Consistency index and apparent viscosity increased significantly with pulp content and decreased with average particle size. The effect of pulp weight fraction (P) on relative viscosity (η_r) could be described by the single parameter equation: η_r= [1 – (P/A)]⁻², while the effect of particle diameter on η_r could be described using Peclet number. Magnitudes of yield stress determined directly by the vane method were higher than those obtained by using the Casson model, and were proportional to the square of pulp content. Reduced Casson yield stress—P data on purees of both particle sizes followd a single curve. Effects of pulp content and particle size on vane yield stress and apparent viscosity were evident from the correlation forms with high values of R².     

Rheology of Concentrated Tomato-Derived Suspensions: Effects of Particle Characteristics

In the present work, the effect of particle properties on the rheological behaviour of tomato-derived suspensions was investigated systematically. Hereto, a range of relatively monodisperse suspensions, containing either cell fragments or single cells with varying average particle size (～148, 267, 303 and 393 μm) and pulp content (from 25 to 60 wt.%), was prepared by the reconstitution of tomato tissue-based particles in water. The effect of the presence of a serum phase on the rheological properties of tomato-derived suspensions was investigated by the comparison of the rheology of reconstituted tomato purées in water with those in serum. All the tomato-derived suspensions were non-Newtonian liquids exhibiting a yield stress. The flow behaviour could be described well by the Herschel–Bulkley model. The undisrupted network structure of all suspensions could be classified as a weak gel with a rather low critical strain. Particle concentration, size and morphology (surface/shape) turned out to be key structural properties controlling the rheological parameters of these tomato-derived suspensions. Increase in yield stress and storage modulus with particle concentration could be fitted to a power law model. The ratio of static yield stress to dynamic yield stress turned out to be larger for particles with a more irregular, less intact surface, showing the enhanced tendency of the latter particles to build up structure in rest conditions. A unique linear relation was found between the static yield stress and the maximal elastic stress in oscillatory tests, independent of the particle properties. Finally, replacing the serum phase by water led to a substantial decrease in network strength, especially in quiescent conditions.     

高能球磨处理对赣南脐橙全果原浆粒径和流变特性的影响

为了开发柑橘全果产品,降低全果原浆粒径,改善其流变特性,对柑橘全果粗浆进行球磨处理。以赣南脐橙为原料,经粗粉碎后球磨处理不同时间（0、30、60、90、120、150、180 min）,得到不同粒径的全果原浆,研究经球磨处理后赣南脐橙全果原浆的粒径和流变特性的变化。结果表明,球磨处理能有效降低全果原浆的粒径,球磨处理180 min后果浆平均粒径由110.00 μm下降到56.53 μm,整体下降了49%。随着球磨处理时间的延长,全果原浆越来越均匀细腻,且无团聚现象。球磨处理的赣南脐橙全果原浆体系随剪切速率的上升,剪切应力增大,而表观黏稠度下降,出现剪切稀化现象,是一种典型的假塑性流体,具有较好的黏弹性。与未经球磨处理的原浆相比,球磨处理60 min得到的赣南脐橙全果原浆黏稠度最高,凝胶状态最为稳定,适合加工为果酱类黏稠度较高的产品;而球磨处理30 min得到的原浆体系黏稠度最低,但流动性最佳,适合加工为果汁类流动性较好的产品。本实验为柑橘全果产品加工提供了参考依据。     

Physicochemical properties of a dressing-type o/w emulsion as influenced by orange pulp fiber incorporation

A low-in-oil dressing-type o/w emulsion incorporating a rich-in-fiber orange pulp commercial product, either in crude form or following comminution, was prepared and the rheological properties and physicochemical stability of the emulsion were studied. Interactions between the adsorbed at the droplet surfaces yolk proteins and the pulp surface constituents, possibly electrostatic in nature, resulted in extensive droplet aggregation. This was reflected in the dramatic increase of emulsion rheological parameter values, derived by applying the power or the Casson equation to shear stress-rate of shear data. Pulp incorporation resulted in an improvement of emulsion stability against creaming while the stability against droplet coalescence was only marginally affected. In addition, the rheological parameter values of the fortified with pulp emulsion exhibited an appreciable increase with storage, especially in the case of emulsions incorporating the crude pulp. These findings are combined with oil droplet or pulp particle size and ζ-potential data to probe the emulsion structure and explain its behavior during aging.     

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.     

Rheological characterization and electrokinetic phenomena of charged whey protein dispersions of defined sizes

A multi-step processing technique produced large colloidal particles from whey proteins, prompting instantaneous thickening upon hydration. Analysis of the rheological characteristics and zeta potential of the modified whey suspensions of defined particle sizes allowed investigation into the role of size on ingredient functionality. Preliminarily, the modified protein powders were sieved to achieve three size ranges, and analyzes were conducted on each of the three distributions and the non-sieved fractions. Following hydration, steady and oscillatory shear analyzes were performed using a controlled stress rheometer to determine rheological characteristics. Intrinsic viscosity was determined with a capillary viscometer and application of the Huggins equation. Zeta potential was calculated from colloidal electrophoretic mobility, measured with a ZetaPALS analyser. After thorough hydration, particle-size analysis revealed a size increase of >1.3 times for each fraction. When analysed on a protein basis, increasing particle size yielded an increase to intrinsic viscosity, flow behavior index, zero shear viscosity, and a decreased zeta potential and consistency coefficient. Knowledge of the interrelationship between zeta potential, rheological properties, and particle size of the modified whey ingredient will further advance an understanding of the functionality of this protein ingredient.     

EFFECT OF PECTIN CONTENT ON FLOW PROPERTIES OF MANGO PULP CONCENTRATES

The effect of pectin on the flow properties of mango pulp concentrates was studied using a coaxial cylindrical viscometer in the temperature (T) range 303-343°K. The variables were soluble solid content(C) 16-30°Brix, pectin content (C_pec, range 0.0323-0.0349 dry wt fraction) for the shear rate (γ) range 9.0-250 s^-1. Mango pulp concentrates behaved as pseudoplastic fluids in the entire pectin content range with a flow behaviour index of 0.286. A model relating shear stress () with the above variables is presented:     

YIELD STRESS OF STRUCTURED AND UNSTRUCTURED FOOD SUSPENSIONS

Yield stresses of 40 model suspensions of apple pulp particles with unimodal and bimodal particle size distribution in water, of 13 commercial food suspensions, and of 11 prepared apple sauce samples were determined by the vane method (_0V), and by application of the Casson (_0C) model. For the unstructured (US) apple pulp suspensions magnitudes of _0V and _0C were nearly equal, but for the structured commercial and prepared apple sauce samples, magnitudes of _0V were much higher than _0C. The ratio of _0V/_0C can be used to determine the shear diameter and the degree of structure of a suspension. Energy dissipation due to viscous drag was also higher for the structured suspensions than for the US suspensions. The results suggest that some trends observed with rheological properties of nonfood suspensions may not be applicable to structured food suspensions.     

Separating the Role of Particles and the Suspending Fluid for the Flow of Soy Milks

The paper describes a model and a simple experimental method to determine suspension transport properties, separating the role of particles from the suspending fluid. Shear stresses are described as consisting of 2 components: 1st, a shear stress caused by the flow of the suspending fluid and 2nd, a shear stress caused by direct interaction between suspended particles. We show that the determination of these shear stresses of a complex (food) suspension is largely independent of the definition of its suspending fluid. The rheological behavior of soy milks at low and intermediate moisture contents was studied, and results are compared with those obtained previously. The method evidences that the high viscosity of soy milks is predominantly caused by direct particle interaction.     

Rheological Properties of Gellan Gels Containing Filler Particles

ABSTRACT: Influences of rigid (glass) and deformable (gellan) particles dispersed in gellan gels were studied to better understand the effect of structure on the rheological properties of model composite foods. Composites with inclusions at 0%, 10%, 20%, and 30% volume fractions (VF) were tested under small deformation oscillatory shear. In gels containing rigid particles, the dynamic shear storage modulus (G') decreased initially, exhibited a minimum around 20% VF, then increased at 30% VF behavior that was attributed to physical interactions among particles. In gels containing deformable particles, the linear decrease in G' with increasing VF may be due to particle compliance under stress or to particle separation from the matrix, thereby causing gel weakening.     

高压射流磨处理对燕麦浆稳定性的影响

目的：研究高压射流磨对燕麦浆稳定性的影响及机制,为全谷物饮料加工提供依据。方法：采用不同压力高压射流磨对燕麦浆进行处理,比较贮藏期（30 d）的形态、不稳定指数、粒径、流变特性变化,并对微观形貌（光学显微镜、激光共聚焦扫描显微镜、扫描电子显微镜）、可溶性成分含量（可溶性固形物、可溶性蛋白、可溶性膳食纤维）进行分析。结果：高压射流磨处理使燕麦浆的粒径、不稳定指数、表观黏度逐渐减小,并能减缓淀粉的老化和颗粒的聚集。高压射流磨能均化蛋白和油脂,破坏细胞壁组织纤维,使更多可溶性物质溶出,并在颗粒内部产生孔腔,增加水合能力,提高体系总体稳定性。结论：高压射流磨技术可提高全谷物产品贮藏稳定性,延长货架期。     

Particle size effects in colloidal gelatin particle suspensions

This paper describes the effects of simple shear flow on the formation and properties of colloidal gelatin particle suspensions. Microscopy and light scattering show that simple shear flow of a phase-separating gelatin-dextran mixture gave smaller particles with a narrower size distribution. Upon gelation due to a temperature decrease, the viscosity of the gelatin increased, which altered the coalescence and break-up behaviour of the particles formed. The small particles obtained by a high shear during processing aggregated into larger particle clusters, once particle solidified upon gelation. The particle size can be predicted using correlation with droplet break-up and coalescence considering the properties before gelation. The sizes of the clusters can be predicted with the coalescence behaviour using the properties after gelation. Clusters originating from small particles resist more deformation, resulting in pronounced rheological effects (e.g. increase viscosity, increased strain softening point).     

Effects of particle size distribution and composition on rheological properties of dark chocolate

Control of chocolate viscosity is vital to its quality and production cost, and directly influenced by solids particle size distribution (PSD) and composition. Effects of PSD and composition on rheological properties of molten dark chocolate were investigated by varying PSD [D₉₀ (90% finer than this size) of 18, 25, 35 and 50 μm], fat 25, 30 and 35% and lecithin (0.3 and 0.5%) using a shear rate-controlled rheometer. PSD, fat and lecithin content significantly affected all rheological parameters, with significant interaction among factors. Increasing particles size gave significant reductions in Casson plastic viscosity, Casson yield value, yield stress, apparent viscosity and thixotropy, with greatest effect with 25% fat and 0.3% lecithin, which reduced with increasing fat and lecithin contents. Statistical analysis revealed that fat exerts the greatest effect on the variability in all the rheological properties followed by PSD and lecithin. PSD, fat and lecithin could be manipulated to control dark chocolate rheology, influencing quality whilst reducing production cost.     

Particle Size Distribution in Tomato Concentrate and Effects on Rheological Properties

The particle size distribution of a tomato concentrate was determined by wet sieving. Wet sieve fractions were then investigated by microscopy and a method based on laser diffraction. Both methods showed that the size of many particles was considerably larger (up to two to three times) than the diameter of the pores through which they have passed during wet sieving. This was explained by the deformability of the tomato cell wall. Effects of particle size distribution on rheological properties were studied by standardizing wet sieve fractions (dry matter, pH). Highest values for yield stress and apparent viscosity were found for the 90–125 and 125–180 μm wet sieve fractions.     

RHEOLOGICAL BEHAVIOR OF LOQUAT (ERIOBOTRYA JAPONICA) JUICES

The rheological behaviour of two different loquat juices was studied. Juices containing pectins and pulp exhibited non-Newtonian with yield stress behavior. Juices from which pectins and pulp were removed exhibited Newtonian behavior. The Bingham model described the relationship between shear stress and shear rate for the first type of juice and the Newtonian model described the second type. The effect of temperature on the Bingham plastic viscosity and the Newtonian viscosity was described by Arrhenius equation. The effect of soluble solids contents was described by power-law and exponential expressions. Finally, two equations that described the combined effect of temperature and concentration were developed.     

芋头浆的流变特性

研究不同质量分数芋头浆在不同温度下的流变学性质。静态流变性质测定结果表明：在研究的质量分数（10%～30%）和温度（0～80 ℃）范围内,芋头浆是具有假塑性的非牛顿流体,其流变特性服从Herschel-Bulkley模型;随着质量分数的增大,芋头浆的非牛顿性在逐渐增强,浆体的屈服应力和黏稠系数逐渐增大,流变特性指数逐渐减小;随着温度的升高,芋头浆的表观黏度不断降低,浆体的非牛顿性逐渐减弱,黏稠系数逐渐减小,流变特性指数逐渐增大,温度与芋头浆黏稠系数的关系可用Arrhenius方程进行拟合;动态流变性质测定结果表明：芋头浆显示弱凝胶特性。     

Rheological characterization of edible films made from collagen colloidal particle suspensions

A rheological characterization of collagen edible films is proposed through the experimental evaluation of shear elastic modulus, toughness, hydration capability and stress and stretch ratio at fracture. These properties are obtained from hydration, simple extension and compression tests and analyzed through the BST (Blatz, Sharda, & Tschoegl, 1974) hyperelastic model. Also precursor collagen particle suspensions, with solid concentrations in the range 0.5–4% w/w, are studied to evaluate their thixotropic responses in sudden imposed shear rates and shear loops. These responses are a consequence of particle aggregations leading to cluster formations. The particle size distribution function of suspensions is determined via scanning electron microscopy. Films are formed by casting and then fixed through either a coagulation process with a salt solution or a chemical process involving covalent cross-links with glutaraldehyde. Results indicate that these collagen films behave as colloidal particulate networks composed of particles and clusters. Also it is found that the fractal dimension of clusters is an intrinsic property of collagen particle suspensions, independently from the maturation time. Clusters in these suspensions are formed with a rather open architecture (low fractal value) due to rather large particle attractive forces. The evaluation of the BST rheological parameters allows one the estimation of the energy amount required to get film fracture for different collagen and cross-linker concentrations. Since the final films have to satisfy several quality requirements before using, the interplay between their stiffness and toughness is presented and discussed.