Relationship between In-line Viscosity and Bostwick Measurement during Ketchup Production

ABSTRACT:  The Bostwick consistometer remains an integral part of assessing the consistency of tomato products in the factory. This work addresses the blending of tomato pastes, packed at different Bostwick readings, for use in tomato ketchup production. The objective of this study was to correlate in-line viscosity measurements of 12 °Bx tomato concentrates to final product quality. Five blends of tomato concentrate were prepared by blending 2 pastes and diluting the mixture to a soluble solids level of 12 °Bx. In-line viscometry measurements at process temperature were made using magnetic resonance viscometry. The resulting Herschel–Bulkley parameters were used to evaluate an apparent viscosity at a characteristic shear rate. The apparent viscosity and Bostwick measurement for the blends were correlated based on a gravity current flow analysis, yielding a coefficient of determination of over 0.99. Ketchup was made from the tomato concentrate blends at 3 levels of natural tomato soluble solids (NTSS). The ketchup Bostwick measurement was then correlated to the ratio of (η/ρ)^−1/5 of the 12 °Bx tomato concentrate yielding coefficients of determination of 0.97, 0.97, and 0.91 for NTSS levels of 6%, 7%, and 7.8%, respectively. This study demonstrates that final product quality can be predicted from in-line viscosity measurements of an intermediate product.     

RHEOLOGICAL BEHAVIOUR OF KIWI FRUIT JUICE CONCENTRATES

The rheological behaviour of diluted kiwi concentrates (22.5–63.0 °Brix) over the temperature range 4 to 70C, was studied. The values below 55.7 °Brix fit the power law while above 55.7 °Brix fit the Herschel-Bulkley equation. Maximum and minimum consistency index values were 62225 and 16 mPa. s ⁿ . Concentrates showed a yield stress at 55.7 °Brix, from 5 to 11 Pa, and 63.0 °Brix, from 19 to 53 Pa. Yield stress was correlated with temperature by means of a linear equation. Arrhenius activation energies were in the range of 28.97 to 33.89 kJ/mol. The average value of the flow behaviour indexes varied from 0.85 (sample at 22.5 °Brix) to 0.59 (sample at 63.0 °Brix). Simple equations are proposed to describe the combined effect of temperature and soluble solids content on consistency index and rheological behaviour index.     

FLOW BEHAVIOR OF GUAVA PUREE AS A FUNCTION OF TEMPERATURE AND CONCENTRATION

Flow behavior of guava puree was determined with a tube viscometer. The puree samples (9.8-16.0° Brix) exhibited shear-thinning behavior. The flow behavior index of the power law model was nearly constant for all the samples over a temperature range of 25-60°C; its mean value was 0.43 with a standard deviation of 0.031. The apparent viscosity decreased with increase in temperature and the activation energy offlow was found to be 3.7 kcallg mole. The apparent viscosity increased as the concentration of the purees was increased; the increase was proportional to concentration raised to a power of 2.7. The Mizrahi-Berk model described well the flow data of the purees. The magnitude of the shear rate exponent was about 0.48, indicating that the purees were suspensions in shearthinning media.     

IN-LINE MONITORING OF TOMATO CONCENTRATE PHYSICAL PROPERTIES DURING EVAPORATION

This work continues the development of an ultrasonic sensor system for in‐line measurement of the physical properties of fluid foods. The test system was a semi‐batch evaporator in which juice from three varieties of processing tomatoes was concentrated from 5 to 24 Brix. The physical properties of the tomato concentrates were measured and correlated to ultrasound properties. Speed of sound was linearly correlated with density, soluble solids content and total solids content of the tomato concentrates. Shear viscosity of the tomato concentrates flowing in viscometric pipe flow was evaluated using ultrasonic Doppler velocimetry (UDV). The UDV technique combines a fluid velocity profile and a simultaneous pressure drop to create a rheogram. Simple shear viscosity was modeled as power law behavior for tomato concentrates as a function of solids content for the three processing varieties. Off‐line measurements of apparent viscosity were well correlated to the in‐line measurements.     

QUALITY DIFFERENCES BETWEEN FRESH PACK AND REMANUFACTURED TOMATO SAUCE

Tomato sauce can be made directly from fresh tomatoes during the tomato season, which is referred to as the fresh pack method, or made from tomato paste that has been diluted back to sauce after the season ends, which is referred to as the remanufactured method. The objective of this study was to determine if the two methods produced significant quality differences either initially or after use by the consumer, such as baking on a pizza. Particle size, viscosity and the concentration of volatiles responsible for fresh tomato flavor decreased during processing to 8°Brix then remained constant. Color, lycopene, volatiles, syneresis and HMF showed no significant difference between fresh pack sauce and remanufactured sauce. Remanufactured sauce had smaller particle size and a lower viscosity than fresh pack sauce. Baking did not create or decrease differences between the sauces.     

Rheological behaviour of blueberry cloudy juice (Vaccinium corymbosum L.)

The rheological behaviour of blueberry cloudy juice ( Vaccinium corymbosum L.), prepared from fresh berries, was studied as a function of solids concentration, in the range 25–61 °Brix, at different temperatures (5–50 °C), with a control rate (CR) rheometer. Cloudy juice was concentrated by vacuum evaporation, and solutions at other concentrations were prepared from the concentrate by adding the liquid collected as distillate. The juices were slightly thixotropic between 45 and 61°Brix. For lower concentrations, the thixotropy was low and could be easily eliminated by shearing. The power law model was applied to fit the pseudoplastic behaviour. The activation energy for flow, evaluated with the Arrhenius–Guzman equation, increased with solids concentration and ranged from 4.6 to 24 kJ gmol^–1. A non-linear correlation, accounting for temperature and concentration effects on the consistency coefficient, was identified.     

EFFECT of PROCESSING CONDITIONS ON the PHYSICOCHEMICAL and SENSORY CHARACTERISTICS of STANLEY PLUM PASTE

Stanley plums were processed into pastes by heat concentration to 25 and 30°Brix. the soluble solids of these two pastes were increased to 40 and 45°Brix, respectively, by sugar addition. the influence of processing techniques on the physicochemical and sensory characteristics of pastes was evaluated. Heat concentration resulted in a significant decrease in titratable acidity, total anthocyanins and total pectin. Pastes showed pseudoplastic behavior within the shear rate range of 20 to 100 rpm. Sugar addition had darkening effect on color, but no noticeable effect on rheological properties of the pastes. It was not feasible to concentrate plum pastes beyond 40°Brix. Paste pH was not affected by processing conditions. Sensory evaluation indicated that preference could be adequately predicted by flavor and color under the condition that °Brix/acid ratio was suitable.     

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).     

Rheological Behaviors of Sumac Concentrate

The individual and interactive effects of temperature (20–50°C), and total soluble solids (TSS) (50–70°Brix), on rheological characteristics of sumac (Rhus coriaria) concentrate were studied using a computer controlled rheometer. Sumac concentrate exhibited Newtonian characteristics for TSS of 50–60°Brix, with a slight deviation corresponding to 70°Brix. The rheological parameters met the criteria of good fit (r² > 0.9983) and provided information for characterizing the effect of temperature and TSS on the flow behavior of sumac concentrate. It was observed that TSS, and temperature considerably affected the apparent viscosity index individually.     

CREEP AND DYNAMIC RHEOLOGICAL BEHAVIOR OF TOMATO CONCENTRATES: EFFECT OF CONCENTRATION AND FINISHER SCREEN SIZE

Based on laser diffraction, pulp particles > 900 μm were detected in tomato concentrates; particles greater than 100–200 μm were found in serum from a concentrate. Creep-compliance and dynamic rheological data showed that viscoelastic properties of 21 °Brix tomato concentrates using a 0.84 mm finisher screen were higher than those from a 0.69 mm screen. Both types of viscoelastic properties were sensitive to increase in concentration in that they increased with increase in Brix of the concentrates. Magnitudes of instantaneous modulus (G₀= 1/J₀) of the tomato concentrates were of the same order of magnitude as the storage modulus (G') at 1 rad s^-1.     

RELATIONSHIP BETWEEN THE BOSTWICK MEASUREMENT AND FLUID PROPERTIES

Consistency of tomato concentrates was evaluated in a Bostwick consistometer. The concentrates were produced in a semibatch evaporator at soluble solids content from 5.3 to 24.0°Brix. The apparent viscosity, yield stress and density were measured at 20C. With respect to the gravity current analysis, the Bostwick measurement correlated well with the theoretical ratio of the apparent viscosity to density (R² = 0.96). For the concentrates with yield stress values in the range of 60–200 Pa, the predicted extent of flow based on the slump analysis was within 2% of the measured extent of flow in the Bostwick consistometer.     

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.     

Effects of temperature,shear rate and constituents on rheological properties of tahin (sesame paste)

In this paper, rheological properties of tahin are reported at temperatures from 20 to 70 °C and shear rates in the range 0.13–500 s^?1. Temporary hysteresis loops were observed in the first cycle of the flow curves. The steady shear behaviour of tahin was pseudoplastic and described by a power law model. The consistency coefficient exhibited strong temperature dependence for which the activation energy of flow was 21.6 kJ mol^?1. The flow behaviour index of tahin tended to increase whereas the consistency coefficient tended to decrease during storage at room temperature. Tahin oil exhibited Newtonian behaviour with a strong dependence of viscosity on temperature. The activation energy of flow for tahin oil was 35.7 kJ mol^?1. While reconstituted suspensions containing up to 20% solids exhibited Newtonian behaviour, those with more solids and the original tahin showed pseudoplastic behaviour. The Krieger–Dougherty model fitted the suspension viscosity data well. Below 20% solids level there was no effect of particle size on the viscosity of the reconstituted suspensions. It was shown that for the same amount of solids the viscosity of a ‘polydisperse’ suspension was lower than that of a ‘monodisperse’ suspension. Copyright © 2004 Society of Chemical Industry     

DEVELOPMENT AND PROCESS OPTIMIZATION OF RED RADISH CONCENTRATE EXTRACT AS POTENTIAL NATURAL RED COLORANT

Red radish concentrate extracts produced from two radish cultivars, red-skinned cv. Fuego and red-fleshed cv. Chinese Red Meat, were evaluated as potential sources of natural colorants. Unit operations were developed and optimized. Anthocyanins were extracted using a modified abrasive peeler or a hammermill for cultivars Fuego and Red Meat, respectively. The anthocyanin extract was further purified by standard juice processing operations and concentrated by conventional evaporative technology and/or direct osmosis. Anthocyanin recoveries of 80–90% as compared to solvent/resin purification were obtained. Anthocyanins extracted from epidermal tissue resulted in juices with fairly low initial °Brix (1.3°), which facilitated juice concentration to levels of 17° Brix containing 400 mg anthocyanin/100 mL concentrate. Radish concentrate provided color similar to FD&C Red #40. Sensory analysis showed     

The role of particle size distribution of suspended solids in defining the flow properties of milk chocolate

The flow characteristics of molten milk chocolate, like most dense suspensions, are a function of the maximum packing fraction ((_m) of the suspended solids. Milk chocolates were prepared from mixtures of two relatively narrow coarse (d_4,3 = 17 μm) and fine (d₄,₃ = 8.5 μm) size distributions of non‐fat solids to contain 0, 25, 50, 75, and 100% of the coarse component. Solids bed density (a measure of maximum packing fraction) correlated with the apparent viscosity of milk chocolates (r = ‐0.98). The highest value for solids bed density and lowest value for apparent viscosity were measured for size distributions with 75% of solids from the coarse fraction. Casson yield value correlated with d_4,3 (r = ‐0.98) and specific surface area (r = 0.93). The maximum packing fraction of binary mixtures of two distinct sizes of non‐fat chocolate solids attained a maximum value for a specific volume ratio of the components. The maximum in _m corresponded with the minimum viscosity in molten chocolate at a given solids volume concentration.     

RHEOLOGY OF MULBERRY PEKMEZ

The rheological behavior of mulberry pekmez (concentrated mulberry juice, °Brix = 72.0) with different solid contents (62.8, 55.8 and 46.0) was studied over the temperature range of 10, 20, 30, 40, 50 and 60C using a Controlled Stress Rheometer. Mulberry pekmez was found to exhibit Newtonian behavior. The effect of temperature can be described by means of Arrhenius equation. The activation energies for flow of samples vary from 53.11 to 12.73 kJ/mol depending on soluble solid contents. The effect of soluble solids on viscosity can be described by an exponential equation. The best model to describe the combined effects of temperature and soluble solids content on viscosity is η= 3.40 X 10^-10 exp (0.12C + 3723/T).     

EFFECTS OF pH ON QUALITY OF STORED TOMATO JUICE

Tomato juice was prepared by the hot-break method and filled hot into cans containing sufficient concentrated HCl to adjust pH to 4.0, 3.5, 3.0, 2.5 and 2.0. Controls were also prepared with no HCl added. Product was stored at ambient (18–22°C) and 40°C up to 3 months. As pH decreased below 4.0, consistency also showed a significant decline through pH 2.0. At the same time there was no apparent pH effect on serum viscosity. Further studies indicated that this effect was noticeable after 4 hr, at pH 3.0 to 5.0. Addition of as much as 1% NaCl to tomato juice had no effect on consistency of tomato juice. Lightness (Hunter color L ) decreased with pH after 3.5, redness (a_L) decreased after pH 4.0, and yellowness (b_L) decreased after pH 3.0. All storage effects were more profound at the higher temperature. The storage of tomato juices at pH less than 4.0 does not appear to be advantageous to the processor.     

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.     

Viscosity Reduction by Homogenization of Orange Juice Concentrate in a Pilot Plant Taste Evaporator

Controlling viscosity is critical to efficient evaporation and pumping of citrus concentrates. Viscosity was reduced by a commercial homogenizer installed between the third and fourth stage of a pilot plant TASTE evaporator. Juice was concentrated to 65°Brix with and without homogenization. The results showed a 13% decrease in viscosity due to homogenization. Mean non-homogenized values were 279 mPa.s (s.d. = 7.5) on the 65°Brix control and 242 mPa.s (s.d. = 10) on the homogenized concentrate, both measured at 3.50 set¹, which was calculated to be the shear rate for these samples within the third stage of this evaporator. This decrease in viscosity also reduced the energy consumption about 3 to 4% or produced a higher (2 to 3) °Brix concentrate. Homogenization did not significantly affect the juice color, acid, pulp or vitamin C.     

EFFECT OF TEMPERATURE ON VISCOSITY OF FRUIT JUICES AND PUREES

SUMMARY: The viscosities of selected fruit juices and purees were measured with a coaxial-cylinder viscometer in the temperature range 20–70°C. Depectinized apple juice and Concord grape juice were Newtonian fluids at all concentrations and their viscosity decreased considerably at higher temperatures. Cloudy apple and orange juices changed from Newtonian to pseudoplastic at concentrations higher than 50 and 20° Brix. respectively. Temperature had a smaller effect on viscosity of cloudy juices than of clear juices. The apparent viscosity of fruit purees (pseudoplastic fluids) decreased slightly at higher temperatures. The activation energy for flow increased with the juice concentration and decreased with the presence of suspended particles in the fruit product. The data and conclusions are useful in the design and operation of efficient food-processing equipment.