PERCEPTION OF GRITTINESS IN AN OIL-IN-WATER EMULSION

Microcrystalline cellulose was dispersed as a gritty substance in an emulsion, and sensory evaluation was conducted to examine the effect of the presence of oil on grittiness felt in the mouth. Samples were prepared with three types of microcrystalline cellulose of average particle size 14, 38, and 76 μm and with a concentration in water of 0.03–2.7%, with three types of emulsion with an oil-volume fraction of 0.2–0.7, and with three rates of homogenization of 500–15,000 rpm. The flow behavior and loss modulus of each sample were measured and sensory evaluation was made of the perceived grittiness. A multiple regression analysis of the data shows that the proportion of people who could perceive grittiness was influenced by the following factors and in that order: concentration of microcrystalline cellulose, oil droplet size, loss modulus, and particle size of microcrystalline cellulose. The proportion of people who perceived grittiness also increased with increasing oil droplet size. This was conceivably caused by the uneven distribution of microcrystalline cellulose particles promoted by large oil droplets. An equation was developed relating the proportion of people perceiving grittiness to the physical properties of the sample. The result indicates that factors effecting grittiness perception are identical for emulsions, aqueous suspensions, viscous suspensions and gels, studied previously.     

RHEOLOGICAL CHARACTERIZATION OF A MODEL FOOD SUSPENSION CONTAINING DISCS USING THREE DIFFERENT GEOMETRIES

The objective of this study was to characterize the flow behavior of a solid-liquid food model which imitates Mexican sauces. The model food suspension consisted of seeds suspended in a shear-thinning fluid (Avicel and Xanthan gum). The effects of size and particle concentration were investigated using a traditional disc geometry in wide gap (spindle), and a ribbon adapted to a rotational viscometer. The effect of particle size was evaluated in a tube viscometer. Power-law parameters and apparent viscosity were estimated in the shear range of each viscometer. The experimental apparent viscosity showed good agreement with predictions obtained using a theoretical expression of relative viscosity for uniform spheres. In all the viscometers investigated, shear-thinning behavior of the suspension was observed, as the aqueous phase, due to low interactions among particles. The ribbon geometry appears to be the best option for flow characterization of food suspensions containing coarse disc shaped particles.     

EFFECT OF CONCENTRATION ON THE RHEOLOGY AND SERUM SEPARATION OF TOMATO SUSPENSIONS

The °Brix value of the tomato concentrate, from which tomato suspensions were prepared, was shown to have a large effect on the resulting apparent viscosity and storage modulus. The apparent viscosity of a tomato suspension prepared from a 30 °Brix tomato concentrate was only 35% of that of a suspension prepared from a 4.9 °Brix juice, both standardized on the same water unextractable solids (WUS) (0.65%) and total tomato solids (TS) level. After homogenizing the difference in apparent viscosity was only about 10–15%. A similar trend was found for the dynamic moduli. The decrease in rheological parameters of the nonhomogenized suspensions is probably partly related to the decrease in diameter of the tomato particles due to the concentration process. Moreover, microscopic fracture of the cellulosic, microfibrillar network of the cell wall plays a part. Serum separation of diluted nonhomogenized tomato suspensions was higher if made from a concentrate that was concentrated to a higher °Brix value. This phenomenon is discussed in terms of variations in uniaxial compression of the network in the diluted tomato suspensions caused by gravitational force.     

Size,shape, and identity of surface crystals and their relationship to sensory perception of grittiness in soft smear-ripened cheeses

Soft smear-ripened cheeses undergo extensive surface crystallization and radial demineralization of calcium, magnesium, and phosphorus, which likely contributes to radial softening during ripening. Furthermore, anecdotal evidence suggests that grittiness is a common characteristic of smear-ripened cheeses. The primary aims of the present study were to evaluate the intensity of perceived grittiness while assessing other key sensory attributes in US artisanal and European protected designation of origin smear-ripened cheeses, and to relate perceived grittiness to the size, shape, and identity of crystals present in the cheese surface smears. Fully ripened wheels of 24 different varieties of smear-ripened cheeses, 16 produced in the United States and 8 in the European Union, were obtained from retail sources. A trained sensory panel (n = 12) was employed to evaluate intensity of grittiness. Crystals present in the cheese smears were identified by powder X-ray diffractometry and polarized light microscopy, and further evaluated in polarized light microscopy micrographs by image analysis for size and shape characteristics. Mean sensory scores for the 24 cheeses ranged from no perceived grittiness to easily identifiable grittiness. Surface crystals included ikaite, struvite, calcite, and brushite, and mean crystal length and area ranged among cheeses from 27 to 1,096 μm, and 533 to 213,969 μm², respectively. Panel threshold for grittiness occurred at a mean crystal length of about 66 μm and mean crystal area of about 2,913 μm². Cheeses with mean values at or below these thresholds displayed negligible perceived grittiness. In contrast, for cheeses with mean values above these thresholds, the mean sensory scores for grittiness were highly correlated with mean crystal length and crystal area (r = 0.93 and 0.96, respectively). Results suggest that surface crystals in soft smear-ripened cheeses influence sensory perception of texture in complex ways that likely include radial softening and grittiness development. A better understanding of factors that govern surface crystal formation may lead to improved control over crystallization and more consistent cheese texture.     

MEASUREMENT AND PREDICTION OF THE PRESSURE DROP INSIDE A PIPE: THE CASE OF A MODEL FOOD SUSPENSION WITH A NEWTONIAN PHASE

The aim of this study was to measure the pressure drops of a solid-liquid food model and to compare pressure drop estimations obtained from proposed correlations for asymmetric distributed suspensions in a horizontal pipe. The model food suspension consisted of alginate spheres suspended in a Newtonian sugar syrup of medium viscosity. The suspension was pumped into a horizontal pipe and measurements for three different sphere diameters and solid-phase concentrations were carried out. Particle velocity, necessary for pressure drop estimations, was predicted using the Eulerian approach, which assumed solid and liquid phases as continuous. Considerations taken were: one dimensional flow of fluid and particles, drag force acting on the particles and constant pressure drop. The momentum equations were solved by the fourth order Runge-Kutta method. Predicted particle velocities showed a retarded parabolic profile compared to the fluid. Drag expressions used, considerably influenced the predicted particle velocities. Estimated pressure drops for the suspensions using the predicted particle velocities agreed with the experimental pressure drops when the tube-particle diameter ratio was higher than 5.8.     

Rheological Behaviour of an Insoluble Lemon Fibre as Affected by Stirring, Temperature, Time and Storage

In this work, the effect the preparation method (two different stirring systems at two temperatures and times), fibre concentration (between 2% and 3%), temperature (between 10 °C and 50 °C) and storage time (between 24 h and 50 days at 5 °C) had on the flow properties of a suspension of dietary lemon fibre prepared with a 45° Brix sucrose solution were evaluated. This information will be helpful in order to discover the best possibilities of using fibre to increase the viscosity of certain kinds of products, depending on the processing, storage and consumption conditions. The obtained results indicate that all the aspects which contribute to increase component solubilisation and the interaction of the insoluble fraction with the aqueous phase when preparing the suspension, such as a decrease in particle size, a rise in temperature or a longer homogenization time, entail a higher apparent viscosity. Moreover, favoring the solubilisation in the preparation process leads to a more stable rheological behaviour of the suspension during storage. As expected, the apparent viscosity of suspensions was dependent on the shear rate, concentration and temperature. A thixotropic behaviour of fibre suspension was only observed at a very low shear rate (5 s⁻¹).     

EVALUATION OF THE SEPARATE CONTRIBUTIONS OF VISCOSITY AND SWEETNESS OF SUCROSE TO PERCEIVED VISCOSITY,SWEETNESS AND BITTERNESS OF VERMOUTH3

The separate effects of sweetness and viscosity of sucrose on the sensory properties of vermouth were evaluated in systems: (1) varying in sucrose concentration and viscosity (2) with constant sucrose concentration but varying in viscosity, and (3) constant viscosity, but varying sucrose concentration. Twenty-one trained judges rated oral viscosity, sweetness and bitterness, while the physical viscosity of the Newtonian systems was measured by capillary viscometry. Both perceived sweetness and oral viscosity increased, while bitterness decreased as sucrose was increased, and as the physical viscosity of the vermouths increased. However, samples in which viscosity was increased by the nonsweet Polycose® were rated sweeter and less bitter than vermouth solutions of the same sucrose concentration, but lower physical viscosity. Similarly, when vermouths of identical viscosity were compared, the vermouths with higher sucrose concentration were judged to be more viscous. Viscosity alone contributed 20-30% of the perceived increase in sweetness due to sucrose addition. The effect of viscosity in reducing bitterness was of the same magnitude. The increase in perceived viscosity caused by addition of sucrose arose from approximately equal contributions of physical viscosity and sweetness of sucrose.     

THE ROLE OF PARTICLE SIZE DISTRIBUTION OF SUSPENDED SOLIDS IN DEFINING THE SENSORY PROPERTIES OF MILK CHOCOLATE

The melting of chocolate in the mouth is a dynamic process. The time evolution of the perceived flavor and texture of chocolate during fat melting and sugar dissolution has been observed and quantified using time-intensity sensory methodology. Five milk chocolates varying in particle size distribution and rheology were prepared. Additionally, two chocolates varying in particle size were standardized to the same viscosity. Particle size and rheology significantly influenced effort, thickness, chocolate and sweetness attributes, although in some unanticipated ways. Averaging time-intensity responses to produce consensus curves generally yielded the same conclusions as averaging parameters extracted from individual curves. However, the later were amenable to statistical analysis using ANOVA and partial least squares regression. Multivariate analysis was a useful technique for identifying those physical properties most correlated with sensory perception.     

INFLUENCE OF GRANULE SIZE ON VISCOSITY OF CORNSTARCH SUSPENSION

The influence of granule size and size distribution in gelatinized suspensions of 2.6% cornstarch heated at fixed temperatures between 70–90C on the power law viscosity was measured by laser diffraction. In the early stages of gelatinization, where the granule size standard deviation was less than 12 μm, dilatant behavior was observed over the shear rate range 200–1100 _S ⁻¹. At constant starch concentration and without granule rupture, suspension consistency, K, increased exponentially with granule mean diameter while the flow behavior index, n, decreased linearly with increase in the extent of gelatinization and the standard deviation of the granule size. The variation of K with granule size and that of n with standard deviation were found to be independent of temperature over 70–90C. In the later stages of gelatinization, where the granules lose their integrity, suspension viscosity progressively decreased as granule rupture continued.     

EVALUATION OF A SLIDING PIN CONSISTOMETER FOR MEASUREMENT OF THE HARDNESS AND SPREADABILITY OF BUTTER AND MARGARINE

A sliding pin consistometer (SPC) has been shown to be particularly suitable for the assessment of hardness and spreadability of butter and margarine. It appears advantageous over other methods in that it is portable, self-compensating for wear, and is convenient and rapid to use on undamaged samples in their original packaging. Four products, hard and soft butter, and hard and soft margarine, with product temperatures in the range 0.8 to 20.0deg;C, were used. The hardness and spreadability of these products at these temperatures were also scored by a panel of 21 adults using a 9-point scoring scale. SPC measurements explained 96% of the variation in panel scores for both hardness and spreadability. The maximum panel score for spreadability was at an SPC value of 5.5 × 10⁻²N for all four products. The SPC should prove useful to manufacturers of butter and margarine in assessing consumer preference for their products.     

EFFECT OF RHEOLOGICAL INTERRELATIONSHIPS BETWEEN STARCH GEL AND FAT ON THE FAT DISPERSION IN FARINACEOUS GEL MATRIX

The rheological interrelationships between starch gel and fat clearly affected the fat dispersion pattern in the farinaceous matrix when soybean-oil-based plastic fat was dispersed in modified tapioca starch gel. A gradual increase in fat particle size with concomitant decrease in fat particle numbers (=0.95) was seen as both viscosity and rigidity of starch gel were decreased. The fat particle size gradually got larger with an increase in fat hardness and began to increase sharply as the fat reached its plastic range (30–40% solid fat). The fat particle size was markedly reduced as both the starch gel to fat viscosity ratio and the shear rate were increased. The viscosity of fat-starch gel mix was highly correlated with fat particle size (r=0.95). The fat viscosity, the rigidity of gel matrix, and the shear rate applied during dispersion appeared to be the most important rheological parameters which determine the overall dispersion pattern of fat in the farinaceous gel matrix.     

Simulation of the Vacuum Infusion Process using Idealized Components: Effects of Pore Size and Suspension Concentration

Vacuum infusion of porous food matrices (i.e., extruded starch crackers) with calorically dense suspensions of food powders in fat was investigated in an ideal system. Experiments involved infusion of model matrices with lipid suspensions consisting of milled, size-characterized sucrose in corn oil. The influences of pore size/particle size ratio and suspension concentration on the penetration of liquid and particles were determined. A mathematical model that allows prediction of future behavior was fitted to the test results. The model indicates that dry-weight particle penetration is strongly correlated with pore size and independent of initial particle concentration. Infusion of liquid plus particles was increased by raising porosity and lowering particle concentration.     

Extension of Einstein's viscosity equation to that for concentrated dispersions of solutes and particles

A viscosity equation for concentrated solutions or suspensions is derived as an extension of Einstein's hydrodynamic viscosity theory for dilute dispersions of spherical particles. The derivation of the equation is based on the calculation of dissipation of mechanical energy into heat in the dispersion, subtracting the energy dissipation in the portion of solutes or particles. The viscosity equation derived thus was well fitted to the viscosity-concentration relationship of the concentrated aqueous solutions of glucose and sucrose. For the suspensions of bakers' yeast, the concentration dependency of viscosity was expressed well with some modification for the flow pattern around suspended particles. It is suggested that these viscosity equations can be widely applied to both diluted and concentrated dispersions of various solutes and particles.     

THICKENING OF SOY PROTEIN SUSPENSIONS WITH CALCIUM*

The objective of this study was to increase the apparent viscosity of 1-7% soy protein suspensions using calcium. The thickening effect, measured by apparent viscosity, depended upon the calcium concentration. Maximum apparent viscosity was obtained with a calcium to protein molar ratio of 20-50 moles of calcium required per mole of protein (M.W. 100 000) decreased with an increase in the protein concentration. Effective stirring was necessary during and after calcium addition to attain maximum thickening and stability. Heat treatment of the protein suspension prior to calcium addition enhanced the extent of apparent viscosity increase. Higher protein concentration, improved stability of the thickened mixture. The established optimum thickening conditions leading to a stable homogenous suspension involved addition of 12.5 mM CaCl₂ to 5% protein suspension preheated at 80 d?C for 30 min.     

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.     

RHEOLOGICAL PROPERTIES OF NONCOHESIVE APPLE DISPERSION WITH HELICAL AND VANE IMPELLERS: EFFECT OF CONCENTRATION AND PARTICLE SIZE

The proportionality constant, k_s, between shear rate, γ, and agitation velocity, N, for a helical ribbon‐screw (HRS) agitator was 17.8. Using the HRS agitator, values of consistency index K and the flow behavior index n of 14 apple pulp suspensions at seven different solids concentrations and two average particle diameters 0.71 mm and 1.21 mm were determined; in addition, values of the Casson viscosity η_c and yield stress σ_OC were also calculated. The magnitudes of K increased and of n decreased with increase in pulp concentration. Experimental values of the vane yield stress, σ_Oν, measured with a six‐blade vane increased with increase in pulp content. The values of σ_OC obtained using the Casson model were close to the experimental values σ_Oν. The effect of particle size on the relative viscosity, η_r, was correlated with Peclet number.     

Impact of particle size distribution on rheological and textural properties of chocolate models with reduced fat content

ABSTRACT:  With an increasing consumption of lipids nowadays, decreasing the fat content in food products has become a trend. Chocolate is a fat-based suspension that contains about 30%wt fat. Reducing fat content causes an increase in the molten chocolate viscosity. This leads to 2 major issues: difficulties in the process and a loss of eating quality in the final product, reported to have poor in-mouth melting properties, remain hard, and difficult to swallow. Literature shows that optimizing the particle size distribution (PSD), that is, having one with an increased packing fraction, can decrease the viscosity of highly concentrated suspensions. This study focuses on the impact of the PSD and fat content on the rheological properties, melting behavior, and hardness of chocolate models (dispersions of sugar in fat). We show that optimizing the PSD while reducing the fat content to a critical amount (22%wt) can decrease the viscosity of the molten material and reduce the hardness of the crystallized chocolate models. Melting in the mouth, characterized by an in vitro collapse speed, is faster for the samples with an optimized PSD. The decrease in the viscosity by optimizing the PSD in systems with a constant fraction of medium phase is based on the decrease of interparticle contact, reducing the particle aggregates strength, and structure buildup during flow or meltdown. In its crystallized state, the particle network is less interconnected, providing less resistance to breakage and meltdown.     

THE RELATIONSHIP BETWEEN HAZE AND THE SIZE OF PARTICLES IN BEER

Haze measurements have been obtained for suspensions of polystyrenelatex particles of known diameter using two light scattering instruments which measure at angles of 90° and 13° respectively. The results agree well with the theory of light scattering and demonstrate the significant effects of particle size and angle of detection upon the instrumental values for haze. This information has been used to correlate the particle size distributions of a number of beers, as measured by Coulter Counter, with the corresponding, measured haze values.     

CONTRIBUTION OF GLYCEROL, ETHANOL AND SUGAR TO THE PERCEPTION OF VISCOSITY AND DENSITY ELICITED BY MODEL WHITE WINES

The contribution of glycerol, ethanol and sugar to the perception of viscosity and density of model wine (MW) solutions was examined. In study 1, the effects of individual components on perceived viscosity (PV) and perceived density (PD) were studied using 5, 20 or 50 g/L glycerol; 3, 7 or 15% v/v ethanol and 0, 80, 150 or 250 g/L sugar concentrations. In study 2, model ice wine mixtures of 8, 10 or 12% ethanol and 150, 250 or 300 g/L sugar were assessed for PV and PD. The physical viscosity and density of the MWs were also measured in both studies. Across the range of concentrations investigated, sugar influences the perception of viscosity and density the most, ethanol has a moderate effect and the contribution of glycerol is nominal. In model ice wine solutions, PV and PD increased with sugar concentration, but were minimally affected by changes in ethanol concentration. The PV elicited by the model ice wine solutions was well described by a linear model using physical viscosity as the independent variable (r: 0.907). This information may be useful for predicting the sensory properties of the ice wine for quality control purposes.     

Model for Evaluating Turbidity in Cloudy Beverages

A model was developed to simulate diluted emulsions of clouding agents in beverages using uniform latex particles (ULP) at different concentrations and particle sizes ranging from 0.10 to 5.85 μm. The model allows determination of optimum concentration and diameter of suspended particles in diluted suspensions. Turbidity measurements showed that, for a given particle concentration, the haze of a diluted suspension reached a maximum when the diameter of the ULP was decreased to 0.2-0.3 μm. A comparison of typical citrus oil in water beverage emulsions with diluted ULP suspensions showed that, when size of suspended oil globules was varied, a similar optimum particle size was found.