PREDICTING THE ELECTRORHEOLOGICAL BEHAVIOR OF MILK CHOCOLATE

Electrorheology is the study of the effects of electric fields on the flow properties of fluids. These materials generally exhibit an increase in apparent viscosity and a greater yield stress over an unelectrified sample. The phenomenon requires an electric field and polar particles suspended in an insulating oil. A standard concentric cylinder viscometer, fitted with custom made electrical attachments, was converted into an electrorheometer. This system allowed control of DC voltage (0–450 Volts mm^?1), fluid temperature (35C–40.5C), and shear rate (0.022 s^?1– 8.744 s^?1) while observing the resulting effects on the shear stress. Dimensional analysis was used to study the rheological response of milk chocolate when subjected to electric fields. Dimensionless groups were identified to explain the phenomena, and multiple regression analysis was used to predict the electrorheological flow behavior of milk chocolate. Over the ranges of input variables, the electric field-induced forces dominated the rheological response over thermal forces, and a prediction equation for apparent viscosity was developed as a function of electric field strength and shear rate. This mathematical expression allows for prediction of milk chocolate rheology in the presence of an electric field.     

ELECTRORHEOLOGICAL BEHAVIOR OF MILK CHOCOLATE

Electrorheology is an area of study that evaluates changes in flow properties upon the application of an electric field. Electrorheological fluids generally exhibit an increase in apparent viscosity and a greater yield stress over an unelectrified sample. The phenomenon requires an electric field, polar particles in suspension, and an insulating oil. Milk chocolate meets these criteria and displays unique behavior when exposed to an electric field. A concentric cylinder viscometer, fitted with special electrical attachments, was used for data collection. This system allowed for control of the applied dc voltage, fluid temperature, and shear rate while observing the resulting effects on the shear stress. Data analyses show that, at constant temperature, the shear stress increases as the voltage increases. Continued analyses depict that shear stress increases as temperature increases when subjected to a constant shear rate and voltage. These results establish milk chocolate as a bona fide electrorheological fluid. The chocolate industry may benefit from this research by gaining knowledge of a new technique to externally control the flow properties of milk chocolate, allowing the development of unique processes and products.     

A micromechanical based finite element model approach to accurately predict the effective thermal properties of micro-aerated chocolate

Micro-aeration is a method to modify the sensorial attributes of chocolate but also affects the material properties of chocolate, which in turn, determine its material response during manufacturing and oral processes. This study aims to define the effect of micro-aeration on the thermal properties of chocolate by considering the changes of chocolate microstructure due to micro-aeration. Micro-aeration was found to alter the chocolate microstructure creating a layer of a third phase at the porous interfaces, which is argued to consist of cocoa butter of higher melting properties. A multiscale Finite Element Model is developed, which was confirmed by macroscale heat transfer measurements, to parametrically simulate the structural changes of micro-porous chocolates at the microscale level and estimate their effective properties, such as thermal conductivity and specific heat capacity. The developed multiscale computational model simulates the porous chocolate as a two-phase (chocolate- pores) or three-phase material (chocolate-cocoa butter layer- pores). The investigation identified a new, complex transient thermal mechanism that controls the behaviour of micro-aerated chocolate during melting and solidification. The results showed a maximum 13% reduction of k_eff and 15% increase of C_peff with 15% micro-aeration resulting to a slower transient heat transfer through the micro-aerated chocolate. The reason is that the micro-aerated chocolate can store a larger amount of thermal energy than its solid counterpart. This effect slows down the transient heat transfer rate in the chocolate and modifies melting/solidification rate and impacts sensorial attributes during oral processing and cooling during manufacturing.     

THERMAL PROPERTIES OF CHEDDAR CHEESE: EXPERIMENTAL AND MODELING

Thermal properties (thermal conductivity, thermal diffusivity and heat capacity) of Cheddar cheese were measured as a function of cheese age and composition. The composition ranged from 30–60% moisture, 8–37% fat, and 22–36% protein (wet basis). The thermal conductivity and heat capacity ranged from 0.354–0.481 W/m °C and from 2.444–3.096 kJ/kg °C. Both thermal conductivity and heat capacity increased with moisture and protein content and decreased with fat content. The thermal diffusivity ranged from 1.07×10^?7 ? 1.53 × 10^?7 m²/s. There was no significant relationship between thermal diffusivity and moisture, fat and protein content of cheese. No statistically significant effect (at the 10% level) of age (0 to 28 wk) on thermal properties was observed. Models predicting thermal properties as a function of cheese composition were developed and their predictive ability was compared with that of empirical models available in the literature. In addition, several theoretical thermal conductivity models were evaluated for their usefulness with Cheddar cheese. Published thermal conductivity models cannot accurately predict (mean error was from 3.4 to 42%) the thermal conductivity of Cheddar cheese.     

Thermo‐physical properties of composite bread dough with maize and cassava flours

Composite wheat–cassava and wheat–maize flours were produced in ratio 100:0. 60:40, 50:50, 40:60 and 0:100 respectively. Thermo‐physical properties of bread dough were determined. For wheat –cassava composite bread dough, moisture content ranged between 44.02 ± 2.04 to 51.31 ± 2.99% dry basis (db), density (1035.2 ± 20.4 to 975.6 ± 12.6 kg m^?3), specific heat capacity (2.51 ± 0.61 to 3.01 ± 0.42 kJ kg^?1 K) and thermal conductivity (0.362 ± 0.13 to 0.473 ± 0.12 W mK^?1). While wheat–maize mixture gave 44.14 ± 1.94 to 45.09 ± 1.26%(db) of moisture content, 981.4 ± 16.3–960.4 ± 22.5 kg m^?3 density, 1.77 ± 0.17–2.61 ± 0.63 kJ kg^?1 K specific heat capacity and 0.36 ± 0.07–0.39 ± 0.02 W mK^?1 thermal conductivity. Effects of substitutions was significant on moisture content and thermal conductivity of dough while non significant influence was recorded on density and specific heat capacity at P < 0.05.     

Thermophysical Properties of Papaya Puree

The effects of soluble solids content and temperature on thermal properties of papaya puree were studied. Density and specific heat were measured using a pycnometer and differential scanning calorimeter, respectively, while thermal conductivity was measured using a line heat source probe. Thermal diffusivity was then calculated from the experimental results of the specific heat, thermal conductivity, and density. Thermal properties of papaya puree were experimentally determined within a soluble solids content range of 10 to 25 °Brix and temperature between 40 and 80°C. The density, specific heat, thermal conductivity, and thermal diffusivity of papaya puree were found to be in the ranges of 1014.6 to 1098.9 kg/m³, 3.652 to 4.092 kJ/kg °C, 0.452 to 0.685 W/m °C, and 1.127?×?10^?7 to 1.650?×?10^?7 m²/s, respectively. Moreover, the empirical models for each property as a function of soluble solids content and temperature were obtained.     

Thermophysical Properties of Sugarcane,Palmyra Palm,and Date-palm Granular Jaggery

Effect of moisture content on thermo-physical properties of sugarcane, palmyra palm, and date-palm granular jaggery were investigated. Thermal conductivity and diffusivity were determined by line-heat-source transient heat-transfer methodology, while specific heat was calculated from additional data on bulk density of the samples. Thermal conductivity, diffusivity, specific heat, and bulk density was found to vary from 0.08 to 0.39 W m^?1 K^?1, 0.10 to 0.13 × 10^?6 m² s^?1, 1.19 to 2.97 kJ kg^?1 K^?1, and 510 to 1310 kg m^?3, respectively, for a moisture range of 2.0–14.3 (%d.b.); all at an average temperature of 30°C. All these properties except—thermal diffusivity—followed an increasing trend; with the increase in moisture content, each showed a high correlation coefficients. The variation of thermal diffusivity was found to be insignificant.     

Thermal Properties of Sweet Potato with its Moisture Content and Temperature

Thermal properties of sweet potato were experimentally determined and modeled as a function of temperature and moisture content. The purpose is to develop empirical correlations that could predict thermal properties during sweet potato processing. Thermal conductivity from the study was 0.49 ± 0.038 Wm^?1K^?1 (mean ± s.d.), thermal diffusivity was 1.2?×?10^?7 ± 9.05?×?10^?9 m²s^?1, specific heat was 3660 ± 477.4 Jkg^?1K^?1, and density was 1212 ± 73.5 kgm^?3. All properties were determined within temperature range of 20 to 60°C and moisture content range of 0.45 to 0.75 w.b. Prediction models for the thermal properties of sweet potato were developed as a function of product temperature and moisture content with experimental data from this study. Mechanistic models were also developed for thermophysical properties of sweet potato using major food components of the product. Developed models were all presented and compared.     

Influence of local convective heat flux on solidification,contraction and wall detachment behavior of molded chocolate during air cooling

The cooling process is an important step during chocolate production. It influences final product quality characteristics such as gloss, texture and melting behavior. Furthermore, it is a high energy consuming operation and its optimization leads to an increase in energy efficiency of the chocolate production. Dark chocolate was cooled in a pilot-scale cooling tunnel with cooling air temperatures of T_air = 2, 12 and 18 °C and air mean velocities of v_in = 1.5, 3.5, and 6.0 m s⁻¹. Convective heat transfer coefficients at the top and the bottom of the mold were received from model calculations applying a CFD model. Crystallization and detachment behavior from the mold walls were newly analyzed by measuring the damping characteristics of ultrasound waves transferring the filled molds during cooling. In addition, for this-like treated well-tempered dark chocolate, the crystallization and detachment behavior were analyzed in further detail. The convective heat transfer from the bottom of the mold increases in flow direction due to the existence of a typical mold geometry-dependent recirculating zone of the cooling air below the chocolate mold and also dependent on the local air velocity. It was shown that depending on intensity and homogeneity of the heat transfer in the air-cooling phase, the structure density of the chocolate can be increased which has a positive impact on resulting product quality characteristics. Moreover, the detachment of the chocolate from the mold wall was demonstrated to have an optimum for typical chocolate plate formats with 125 g weight at an apparent heat flux of 550 W/m², for which the time until detachment reaches a minimum.     

Determination of the caffeine contents of various food items within the Austrian market and validation of a caffeine assessment tool (CAT)

The caffeine content of 124 products, including coffee, coffee-based beverages, energy drinks, tea, colas, yoghurt and chocolate, were determined using RP-HPLC with UV detection after solid-phase extraction. Highest concentrations of caffeine were found for coffee prepared from pads (755?mg?l^?1) and regular filtered coffee (659?mg?l^?1). The total caffeine content of coffee and chocolate-based beverages was between 15?mg?l^?1 in chocolate milk and 448?mg?l^?1 in canned ice coffee. For energy drinks the caffeine content varied in a range from 266 to 340?mg?l^?1. Caffeine concentrations in tea and ice teas were between 13 and 183?mg?l^?1. Coffee-flavoured yoghurts ranged from 33 to 48?mg?kg^?1. The caffeine concentration in chocolate and chocolate bars was between 17?mg?kg^?1 in whole milk chocolate and 551?mg?kg^?1 in a chocolate with coffee filling. A caffeine assessment tool was developed and validated by a 3-day dietary record (r ^2?=?0.817, p?<?0.01) using these analytical data and caffeine saliva concentrations (r ^2?=?0.427, p?<?0.01).     

HYBRID NEURAL MODELING OF THE ELECTRICAL CONDUCTIVITY PROPERTY OF RECOMBINED MILK

This paper focuses on modeling the electrical conductivity of recombined milk by a hybrid neural modeling technique. It aims to establish a model that accounts for the effect of milk constituents (protein, lactose, and fat) and temperature on the electrical conductivity of recombined milk. Such a model should provide physical insight to the underlying relationship, in addition to its high precision.

A hybrid neural model was established by combining a mechanistic model to explain the major interrelation and an ANN model to deal with the difference and noise. Two mechanistic models and two 4-layer ANN models were developed. The best mechanistic model in terms of the smallest sum square error (SSE) combined a linear equation describing the effect of milk component concentration and a non-linear equation describing the effect of temperature. For this model, the correlation coefficient between the actual electrical conductivity and the modelled electrical conductivity was 0.9878 and SSE was 1.3376. Combining it with the 4-layer ANN model that produced the smallest SSE, the resulted hybrid neural model provided the best performance, with a correlation coefficient of 0.9982 between the actual electrical conductivity and the modelled electrical conductivity and a SSE of 0.1410.

Abbreviations: ANN, artificial neural network; EC, electrical conductivity (mS/cm); c, concentration (mol.m^?3); D, diffusion coefficient (m².s^?1); F, Faraday constant (A.s.mol^?1); ΔG, Gibbs free energy of activation for the reaction (kJ.mol^?1); K, specific conductivity (Ω^?1.m^?1); k, dissociation constant (mol.m^?3); R, ideal gas constant (J.K^?1.mol^?1); T, temperature (K); Λ₀, molar conductivity at infinite dilution (Ω^?1.m².mol^?1); Λ_c, molar conductivity at finite dilution (Ω^?1.m².mol^?1); z _i , charge number     

Thermal Properties of Kerstingiella geocarpa Seeds as Influenced by Moisture Content

The specific heat capacity, thermal conductivity and thermal diffusivity of Kerstingiella geocarpa seeds were determined as a function of moisture content. The initial moisture content of the seeds determined using the ASAE standard test was 10.0 % (d.b). The specific heat capacity of Kerstingiella geocarpa seed increased from 155.83 to 204.45 Jkg^?1k?1, as the moisture content increased from 10 to 30 % (d.b). The thermal conductivity of the seed increased from 5.13 × 10^?2 to 4.87 × 10^?1 Wm^?1k^?1, as the moisture content increased. The thermal diffusivity of the seed increased from 2.35 × 10^?4 to 3.66 × 10^?3 m²s^?1, as the moisture content increased. These values indicate the ability of the Kerstingiella geocarpa seed to retain heat when processed. The regression models that could be used to adequately express the relationships existing between the thermal properties of the Kerstingiella geocarpa seed and moisture content were established.     

THERMOPHYSICAL PROPERTIES OF PINK GUAVA JUICE AT 9 AND 11°BRIX

The effect of temperature on the conservation of pseudoplastic characteristics and on the physical properties of pink guava juice (Psidium guajava L.) variety Beaumont: B‐30 with two different total soluble solids (9°Brix and 11°Brix) was investigated. It was found that the juice exhibits pseudoplastic behavior in the range of shear rate between 40 to 160 s^?1 and within pasteurization temperature of 60–90C. While the flow behavior index (n) and density (p) increased, consistency coefficient (K), thermal conductivity (k) and specific heat capacity (C_p) decreased with increasing temperature. The linear regression equations or models for flow behavior index, consistency coefficient, density, thermal conductivity and specific heat capacity were determined with correlation coefficients ranging from 0.75 to 1.00.     

THERMOPHYSICAL PROPERTIES OF FRESH AND ROASTED COFFEE POWDERS1

The present work deals with experimental determination of bulk specific heat, bulk thermal conductivity, bulk and true density and moisture content of Columbian and Mexican coffee bean powders. Specific heat was determined by DSC, thermal conductivity by modified Fitch apparatus, density by stereopycnometer and moisture contents by standard vacuum oven method. Specific heat values showed marginal rise over the temperature range (45 to 150C) studied. Thermal conductivity values, determined in the temperature range of 20–60C were not found to have any definite trend with rise in moisture in the experimental range of 4.8 to 9.8% moisture (dry basis). Bulk density of powders varied appreciably (1.298 to 0.882 g.cm^?3), while the change was negligible for true density (1.361 to 1.092 g.cm^?3) with the degree of roasting. Statistical analysis of the data shows the reliability of the experimental determinations. Suitable correlations were developed to determine bulk specific heat and bulk density.     

PERFORMANCE MODELS FOR CONTINUOUS DIELECTRIC PASTEURIZATION OF MILK

The steady-state performance of a continuous parallel-plate heat exchanger was generally predicted for nonfat milk solutions of measured conductivity by a model equation obtained from energy balance on the exchanger. Electrical properties of the milk were determined from the Hasted-Debye models for aqueous ionic solutions. Heating characteristics of an experimental exchanger agreed closely with predicted values for various flow rates and voltage gradients at temperatures of interest in pasteurization of biological fluids. Such models could be employed in the development of electrical pasteurization or sterilization processes for a variety of food products. Electrical heating processes would reduce thermal denaturation of heat-labile food constituents, as compared with conventional heating processes, due to rapid heat penetration, uniform heating and low surface temperatures and would give products of improved nutritional value and organoleptic quality. Theoretical considerations also suggest that higher thermal death rates would be obtained for vegetative microbial contaminants at process temperatures and holding times comparable to those of conventional heating processes.     

Survival, growth, and thermal resistance of Listeria monocytogenes in products containing peanut and chocolate

Outbreaks of listeriosis associated with the consumption of ready-to-eat foods have raised interest in determining growth, survival, and inactivation characteristics of Listeria monocytogenes in a wide range of products. A study was undertaken to determine the thermal tolerance of L. monocytogenes in a peanut-based beverage (3.1% fat), whole-fat (3.5%) milk, wholefat (4.0%) and reduced-fat (1.0%) chocolate milk, a chocolate-peanut spread (39% fat), and peanut butter (53% fat). The D60 degrees C value (decimal reduction time at 60 degrees C) in peanut beverage (3.2 min) was not significantly different (P > 0.05) than the D60 degrees C value in whole-fat milk (3.3 min) or whole-fat chocolate milk (4.5 min) but significantly lower (P < or = 0.05) than the D60 degrees C value in reduced-fat chocolate milk (5.9 min). The pathogen was significantly more resistant to heat when enmeshed in chocolate-peanut spread (water activity [aw] of 0.46; D60 degrees C = 37.5 min) and peanut butter (aw of 0.32; D60 degrees C = 26.0 min) than in liquid products. At 10 degrees C, the pathogen grew most rapidly in whole-fat chocolate milk and slowest in peanut beverage. At 22 degrees C, populations increased significantly within 12 and 16 h in whole-fat milk and reduced-fat chocolate milk, respectively, and within 8 h in whole-fat chocolate milk and peanut beverage. Initial populations (3.37 to 4.42 log CFU/g) of L. monocytogenes in chocolate-peanut spread and peanut butter adjusted to an aw of 0.33 and 0.65 declined, but the pathogen was not eliminated during a 24-week period at 20 degrees C. Survival was enhanced at reduced aw. Results indicate that a pasteurization process similar to that used for full-fat milk would be adequate to ensure the destruction of L. monocytogenes in peanut beverage. The pathogen survives for at least 24 weeks in chocolate-peanut spread and peanut butter at an aw range that encompasses that found in these products.     

Effect of temperature and bulk density on thermal conductivity of spray-dried whole milk powder

The thermal conductivity of whole milk powder was determined by a steady-state guarded hot-plate method at temperatures ranging from 11·8 to 43·2°C, at bulk densities 0·512 and 0·605 g cm^?3.It was found that thermal conductivity increased with increasing temperature and with increasing bulk density. Thermal conductivity increased from 0·036 W m^?1 K^?1 at 11·8°C to 0·077 W m^?1 K^?1 at 43·2°C for bulk density 0·512 g cm^?3, while for bulk density 0·605 g cm^?3 thermal conductivity increased from 0·058 W m^?1 K^?1 at 16·6°C to 0·093 W m^?1 K^?1 at 42·8°C.     

Effective Thermal Conductivity of Rice Flour and Whole and Skim Milk Powder

ABSTRACT: The effective thermal conductivity for 3 kinds of powdered food (rice flour, whole milk powder, and skim milk powder) was measured at selected moisture contents, temperatures, and bulk densities. The transient heat probe method using twin probes was used for the determination of the effective thermal conductivity. The effects of moisture content, temperature, and bulk density on the effective thermal conductivity of samples were investigated. The observed values were compared with the values calculated from the thermal conductivity of air and powder, using the 3 kinds of structural model for thermal conductivity, that is, the series, parallel, and random heat transfer models. An improved random heat transfer model, in which a correction term was incorporated in the random heat transfer model, with the term written as a function of moisture content and temperature, was developed.     

Impact of amorphous and crystalline lactose on milk chocolate properties

Chocolate mass of low viscosity is preferred for most applications. Milk powder influences processing behaviour, flow properties and taste of milk chocolate. The project aimed to investigate influences of skim milk powders containing amorphous or crystalline lactose on flow properties after producing samples by roller milling and conching or alternatively by ball milling. For the first case, it was found that mass consistency before roller milling is strongly influenced by lactose type; producers must specify it and adapt initial mass fat content. Little impact on final products was found after processing milk powders at equilibrium moisture. If predried powders are used for reducing conching time, crystalline lactose leads to chocolate with slightly lower viscosity. At ball mill processing, crystalline lactose resulted in significantly lower viscosity, for example 15% at 40 s^?1; thus, for this process, it can be recommended to use special milk powders high in crystalline lactose content.     

SHELF-LIFE EVALUATIONS OF LIQUID FOODS TREATED BY PILOT PLANT PULSED ELECTRIC FIELD SYSTEM

There is a pressing need to validate the shelf-life extension of Pulsed Electric Field (PEF) treated foods. This study was designed to evaluate the shelf-lives of cranberry juice and chocolate milk as a function of PEF and the interaction of PEF+heat treatments. Cranberry juice was exposed to PEF and PEF+heat (60C), and chocolate milk to PEF+heat (105 and 112C). Microbial analysis and color measurement were performed on untreated and treated cranberry juice and chocolate milk aseptically packaged and stored at 4, 22, and 37 C for 197 and 119 days, respectively. Microbial analysis of cranberry juices demonstrated that the shelf-life of PEF and PEF+heat treated juices stored at 22 and 37 C increased significantly during 197 days (p<0.05). The shelf-life of chocolate milk treated by PEF+105C and PEF+112C increased significantly at all storage temperatures (p<0.05). The PEF nor PEF+heat treatments did not result in any significant differences in color retention of either cranberry juice or chocolate milk (p>0.05). This study presented that PEF and PEF+heat treatments were very effective to increase shelf-lives of cranberry juice and chocolate milk.