Steady Shear Rheology and Fluid Mechanics of Four Semi-Solid Foods

The steady shear rheology of four semi-solid food materials (ketchup, mustard, apple sauce and tomato paste) was studied by generating and comparing flow data using cone and plate, parallel plate and capillary measurements over the shear rate range of 0.05–1600 see^?1. Super-position of flow data was demonstrated and correlations obtained; using the power law, Bingham Plastic, Herschel-Bulkley and Casson models were compared. In the low shear rate range (y = 0.05 – 1.0 set^?1), the Bingham Plastic model and in the high shear rate range (y = 1.0 – 1600 sec^?1), the Herschel-Bulkley model were shown to be most successful. Comparison of average velocity data with mathematical predictions using the power law, Herschel-Bulkley and Cas-son models showed that the equation using the Herschel-Bulkley model was best and should be used in the design of flow processes for the foods studied.     

AN ATTEMPT TO IDENTIFY AND MODEL TRANSIENT VISCOELASTIC FLOW IN FOODS2

Shear stress development data for commercial ketchup, mustard, mayonnaise, apple butter, butter, margarine and canned frosting were obtained using the cone and plate geometry of the Rheometrics Mechanical Spectrometer. At sudden imposition of four shear rates, .1, 1, 10, and 100 s^?1, shear stresses displayed different degrees of overshoots with margarine exhibiting a maximum overshoot of 320% that of the steady-state value at a shear rate of 100 s^?1. The actual extent of overshoot depended on the particular food and the particular shear rate applied. An attempt was made to explain observed transient shear stresses with the Bird-Leider equation, a four parameter empirical model which incorporates both steady viscous and elastic properties of food materials. This model assumes both the steady viscosity function, η, and the steady primary normal stress coefficient Ψ to have a prominant power-law region with increasing shear rate. This assumption is shown to be justified for all foods studied between shear rates of .1 s^?1 and 100 s^?1. When this assumption is justified a time constant Λ can be constructed. This time constant is found to be an approximate indicator of relative stress overshoot for the foods studied. It is found that the Bird-Leider equation provides a moderately good prediction of peak shear stresses and peak times and only a crude prediction of shear stress decay. Nevertheless, the model is a definite improvement over time independent models such as the power-law model.     

FLOW PARAMETERS OF SELECTED COMMERCIAL SEMI-LIQUID FOOD PRODUCTS2

The rheological characteristics of samples of commercial apple sauce, baby food (banana and peach), mustard and ketchup were evaluated by two successive shearing cycles in a coaxial viscosimeter. It was found that generally, both the Herschel-Bulkley and the modified Casson equations were equally good mathematical representatives of the experimental flow curves, especially after the sample has already been sheared once. The original Casson equation was generally a lesser appropriate model especially for the first flow curve. Time and shear effects on the flow curve features, and on the magnitude of the yield stress, were also studied. The results showed that although all the effects were roughly on the same order of magnitude, they varied considerably between the different types of products and within the same products of different manufacturers.     

MIXER VISCOMETRY to CHARACTERIZE FLUID FOODS WITH LARGE PARTICULATES

Mixer viscometry is an effective means of characterizing fluids containing particulates. an interrupted helical screw impeller used to determine the flow behavior of fresh concrete was scaled‐down to analyze fluid foods with large particulates. the mixer viscometer constant was determined to be 1.6 rad^?1 by the matching viscosity method. Large particulate food materials successfully investigated in this study included cream corn, salsa, smooth pasta sauce and chunky pasta sauce. Apparent viscosity curves were constructed from torque and angular velocity data. Testing materials exhibited shear‐thinning behavior and temperature dependence. Analysis revealed K and n values ranging from 10.1 Pa sⁿ to 40.3 Pa sⁿ and 0.17 to 0.36, respectively. Regression control charts, based on apparent viscosity and average shear rate data were constructed for each product. A protocol is presented for producing and utilizing these charts as a statistical quality control tool for industry.     

EFFECT OF PROCESSING CONDITIONS ON THE COMPOSITION AND RHEOLOGICAL PROPERTIES OF APPLESAUCE

The relation between the composition and rheological properties of applesauce was studied in two ways. For artificial applesauces, reconstituted from isolated applesauce particles and applesauce serum, the residual shear stress increases exponentially with pulp content. Below a particle size of 0.625 mm the values of residual shear stress and apparent viscosity are lower for smaller particles. The effect of the processing conditions (finisher screen openings and cooking time) and raw material (apple variety and ripeness) on particle size and pulp content was studied on sauce made in a pilot plant. The particle size and pulp content of these applesauces affect the rheological properties in the same way as was shown for the artificial applesauces.     

Influence of cultivar, fruit maturity and fruit anatomy on apple sauce particle size and texture

Particle size distribution, which largely determines the texture of finished apple sauce, was studied in relation to the fresh fruit properties of five apple cultivars. The different effect that continuing fruit storage has on particle size distribution of the sauce, depending on cultivar, is reported. Light microscopy supported the conclusion that the cell wall components affecting the separation of cells, and possibly re-aggregation in some instances, are mainly involved in these commercially important variations in texture. The possibility that vascular tissues in the fruit and starch granules in the cells may be other, lesser contributors to sauce texture is discussed. The study emphasizes the cultivar dependency of the properties reported.     

FLOW BEHAVIOR of TOMATO SAUCE WITH OR WITHOUT PARTICULATES IN TUBE FLOW1

Viscosity and density are two properties of fluids that are affected by temperature changes. the flow behavior of tomato sauce (7° and 14° Brix) in a tube viscometer was studied at varying concentrations of added particulates (2 and 5 wt%) at temperatures in the range of 70 to 95°C. the results indicate that the Power Law model described the flow behavior of the non-Newtonian fluids better than the Casson model. the effects of temperature, concentration of carrier fluids and particulates on the flow behavior indices and viscosity was studied. the effect of temperature on the flow behavior index (n) and consistency index (K) were modeled as exponential relationships. the values of n and K for 7° Brix sauce ranged from 0.30 to 0.86 and 0.04 to 0.34, respectively. For the 14° Brix sauce these values were 0.27 to 0.53 and 0.20 to 0.60 respectively. the values of n decreased and K increased with increase in concentration of solids and particulates. the relative changes in K and n were lower for higher concentrations of solids and particulates. It was found that temperature had a greater effect on K than on n. The effects of temperature on viscosity was modeled as an Arrhenius type equation from which the activation energies were calculated. the combined effects of temperature, concentration of solids in the sauce and added particulates on apparent viscosity can be predicted by a nonlinear model.     

Role of Pulp Content and Particle Size in Yield Stress of Apple Sauce

A paddle mixer in conjunction with a rotational viscometer was used to determine the yield stress and the shear rate-shear stress data of apple sauce. Magnitudes of yield stress obtained by extrapolation of the shear rate-shear stress data according to Casson, Herschel-Bulkley, and Mizrahi-Berk models were considerably lower than the experimental values. The experimental values were closer to the Bingham yield values obtained by extrapolation of the straight line portion of the shear rate-shear stress data. Pulp content and average particle size of the solids affected the magnitudes of the yield stress.     

Rheology of Apple Sauce: Effect of Apple Cultivar, Firmness, and Processing Parameters

Shear rate-shear stress data of 54 samples of apple sauce and their serums were determined, and power law parameters were derived for the data. The samples were from two apple cultivars (Rome Beauty and Rhode Island Greening) that were stored to three firmness values and processed utilizing three finisher screen sizes and speeds. Serum samples were mildly non-Newtonian, while the sauce samples were highly non-Newtonian fluids. Analysis of variance showed that apple cultivar, apple firmness and finisher screen opening accounted for a large variation in sauce consistency, while regression analysis showed that pulp content was important for the magnitude of the sauce consistency.     

Rheological,Textural and Flavour Properties of Yellow Mustard Sauce as Affected by Modified Starch,Xanthan and Guar Gum

Influence of a modified starch-gum thickening system on the rheological, textural and flavour properties of yellow mustard sauce was studied. The rheological measurements indicated that the sauces exhibited a weak gel-like, strong shear thinning behaviour. Dynamic viscoelasticity measurements showed that the sauces with modified starch (MS) and xanthan gum (XG) presented superior viscoelastic properties to those with MS and guar gum (GG) samples. All tested sauces showed non-Newtonian, pseudoplastic and thixotropic fluids characteristics. Parameters such as hardness, springiness, cohesiveness, gumminess and spreadability were used to evaluate the textural properties, and the results indicated that MS/XG was more influential than MS/GG on the textural properties. Sensory analysis suggested that 0.4 % MS/0.3 % XG, 0.4 % MS/0.4 % XG and 0.4 % MS/0.4 % GG were superior thickeners for the yellow mustard sauces. The flavours of these three sample groups with the highest sensory scores and a sample with only MS were analysed by an electronic nose, which showed that the electronic nose was able to distinguish their differences.     

甘油与鲁氏酵母共固定在高盐稀态酱油酿造中的应用

本文旨在研究相容性溶质之一的甘油对高渗透压环境下鲁氏结合酵母的保护作用,以及将甘油与鲁氏结合酵母共固定对高盐稀态酱油发酵的影响。添加不同浓度甘油至含3 mol/L氯化钠的YPD培养基中,观察酵母菌生长情况。同时,共固定甘油与鲁氏结合酵母,应用于高盐稀态酱醪发酵。结果显示,1.37 mmol/L甘油即可有效缓解高盐环境对鲁氏结合酵母的生长抑制作用,生长延滞期缩短达4~6 h。高盐稀态酱油发酵中试结果显示,与空白对照组相比,试验组蛋白质转化率提高幅度达2.23~5.64%,头油中各理化指标平均提前15 d达到空白组相同水平。综上所述,甘油作为一种相容性溶质可有效保护高盐环境下鲁氏结合酵母的生长繁殖,及其在高盐稀态酱醪发酵中的代谢性能,甘油与鲁氏接合酵母共固定技术能够提高酱油发酵的原料利用率、缩短发酵周期,在酱油酿造领域具有一定的实际应用价值。     

EFFECT OF PARTIAL REPLACEMENT OF SUCROSE BY CORN SYRUP ON QUALITY AND STABILITY OF CANNED APPLE SAUCE

SUMMARY— Apple sauces were made from Gravenstein apples under normal commercial processing conditions, using pure sucrose and combinations of sucrose and 62 D.E. corn syrup as sweeteners. Products were tested for storage stability of 68 and 86°F. Undesirable chemical and physical changes occurred rapidly at 86°F as indicated by the increase of hydroxymethyl furfural, darkening of serum color, decrease in consistency and increased can corrosion. This was accompanied by lower organoleptic color and ffavor scores. It appeared that the quality and storage stability of apple sauce were influenced more by higher storage temperatures and longer storage duration than by the type of sweeteners used in making the apple sauce. For a longer shelf fife and better quality retention, canned apple sauce should be stored at 68° F or lower. Results of this investigation indicate that corn syrup can be used lo replace 25% of the added sucrose in processing apple sauce.     

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.     

Physicochemical properties of cell wall materials from apple, kiwifruit and tomato

Cell wall materials (CWMs) were isolated from the fruit of ripe apple, kiwifruit and tomato using methods of isolation which maximised the water retaining capacity and viscosity generating properties of the CWMs. Aqueous suspensions of all three CWMs were able to form a gel-like matrix at a concentration of 1%. There was a dramatic enhancement in gel firmness of kiwifruit and tomato following a high shear treatment, but no such effect was apparent with apple CWM. Confocal microscopy showed that the shear-induced increase in viscosity was accompanied by fragmentation of the CWMs of kiwifruit and tomato which increased the available surface area for particle–particle and/or particle–solvent interaction. The viscosity of kiwifruit and tomato CWM dispersions was reduced in the presence of electrolytes indicating an important role for the double electrical layer in the gelling properties of the CWMs. The viscosifying properties of apple CWM were however independent of both shear and added electrolyte. This was attributed to the fact that CWM from apple resisted breakup under high shear. The greater connective integrity of the apple cell walls compared to that of kiwifruit and tomato is discussed in relation to differences in ripening induced changes to the pectic polysaccharides of the cell walls.     

Chemical and Physical Treatment Effects on Solid-Liquid Extraction of Apple Tissue

Various experimental treatments have been selectively applied to apple tissue in an effort to determine whether a solid-liquid extraction process could be utilized for manufacturing single strength beverage juice. Vacuum impregnation of enzymatic and chemical solutions showed a positive effect on accelerating the rate of diffusion in the tissues studied. The greatest overall effect on increasing the rate of diffusion was caused by a pretreatment with radio-frequency energy. Observed diffusion coefficients were 4.11 × 10^-6 cm²/sec with this treatment, as compared to 1.20 × 10^-6 cm²/sec for the control group of samples. Pretreatment techniques are suggested to enhance the rate of diffusion in apple tissue that may be of commercial value.     

挤压参数对酱油渣粗纤维含量影响研究

采用挤压膨化技术对酱油渣进行预处理,研究挤压工艺参数对酱油渣中粗纤维含量的影响。在单因素试验的基础上,以挤出物粗纤维含量为考察指标,以含水量、挤压温度、螺杆转速为挤压参数,运用中心组合试验设计（CCD）对挤压酱油渣中挤压参数进行优化。结果表明,最佳挤压膨化参数为含水量32%,挤压温度为100 ℃,螺杆转速为95 r/min。在此优化条件下,挤出物粗纤维含量为19.5%,与挤压膨化前原料相比,粗纤维含量降低了31.3%。该挤压膨化技术可以提高酱油渣的利用率。     

日本利用食品生产废料制调味料

为充分利用食品生产中的废料,该文介绍了日本利用酿酒废液和酒糟制作调味料、米渣蛋白制作发酵调味液、禽畜血制作复合调味粉和海鲜调味废液生产浓缩调味液等方法。     

Modeling Shearing Resistance of Powdery Starch for Simulation Studies of Extrusion Cooking Processes

Modeling extrusion cooking of starch requires the use of appropriate intrinsic kinetic equations. Knowledge of shear stress profile in a particulate system such as that in the transition zone of an extruder is crucial for calculation of degrees of conversion (gelatinization and melting) of starch. Shearing resistance of moistened powder starch as affected by temperature, normal pressure, effective shear rate, moisture content, and degree of starch conversion was studied in a model system. A modified vane shear testing device was used for experimental measurement of each individual effect. Within the experimental ranges studied (temperature 30 to 80°C, moisture content 16 to 35%, effective shear rate 0 to 550 s⁻¹, starch conversion 0 to 0.36 (36%), and normal pressure 0 to 83 kPa) parameter values in each functionality were evaluated. A single mathematical model useful for calculating shear stress was obtained by combining these effects in a single relationship. A good correlation was shown when the calculated shear stress was plotted against the experimentally measured. The methodologies developed here are useful for the studies of powdery food materials. The potential application of this correlation to the simulation of extrusion processes was discussed.     

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.     

酱油酿造中鲜啤酒糟利用的研究

鲜啤酒糟作为辅料用于酱油制曲，不仅可以降低原材料成本，而且容易使曲料处于疏松状态，大大提高制曲过程的通风效率，改善发酵过程的传质和传热效果。各试验组孢子发芽率基本相同，辅料取代率为20％和40％时，其孢子数、成曲和酱油质量与传统配料相当，蛋白质利用率分别为78．04％和78.31％。