SOME THEORETICAL AND EXPERIMENTAL CONSIDERATIONS ON THE THIN-LAYER DRYING OF FISH CRACKERS: PRODUCT EXPANSION ASSESSMENT

Fish crackers are semi-prepared starch-based products which must be expanded just prior to consumption. This work aims at the experimental and theoretical study of the thin-layer drying process of fish crackers in a thin disc geometry. The process was carried out in an insulated cabinet dryer and the experimental kinetic drying data were fitted using the analytical solutions resulting from both a drying model governed by the Fick' s second law and a model based on the lumped system, highlighting the adequacy of each of them. Therefore, it was possible to calculate the mass transfer coefficients for seven different blends offish crackers. Also, the effect of the drying time on the bulk density of the puffed product was evaluated for these seven blends. Both the kinetic drying parameters and the optimal bulk density responses were analyzed using the Simplex-Lattice Design over a mixture triangle within a minimal number of experiments.     

EFFECT OF DRYING METHOD ON SHRINKAGE AND POROSITY

ABSTRACT

The effect of drying method on bulk density, particle density, specific volume and porosity of banana, apple, carrot and potato at various moisture contents was investigated, using a large set of experimental measurements. Samples were dehydrated with five different drying methods: conventional, vacuum, microwave, freeze and osmotic drying. A simple mathematical model was used In order to correlate the above properties with the material moisture content. Four parameters with physical meaning were incorporated in the model: the enclosed water density p_w, the dry solid density p_s, the dry solid bulk density p_bo and the volume shrinkage coefficient β'. The effect of drying method on the examined properties was taken into account through its effect on the corresponding parameters. Only, dry solid bulk density was dependent on both material and drying method. Freeze dried materials developed the highest porosity, whereas the lowest one was obtained using conventional air drying.     

SOME ASPECTS OF MODELLING CONVECTIVE CORN DRYING

ABSTRACT

Specific heat claim of dewatering at large scale convective corn driers could be reduced to about 3000 kf/kg by means of an accurate modelling of the drying process. The main inadequecy of the models used in these days is the ignorance of change caused by interactions between some process parameters and material features during drying process.

In this study dehydration of seven Pioneer type hybrids was tested at model and large scale driers. By an empirical resolution of specific heat and bulk density functions of shelled corn furthermore by establishing a drying speed equation depending on the main grain- and process-features an appropriate result was provided.     

DENSITIES,SHRINKAGE AND POROSITY OF SOME VEGETABLES DURING AIR DRYING

Abstract

Bulk density, particle density, shrinkage and porosity were experimentally determined at various moisture content during air drying for apple, carrot and potato cubes. A simple mathematical model was used to predict the above properties versus material moisture content. Four parameters were incorporated in the model: enclosed water density, dry solids' density, bulk density of dry solids, and volume-shrinkage coefficient. The model was fitted to experimental data satisfactorily, and the parameters were estimated. The influence of varying drying conditions was also investigated.     

DRYING OF BIOACTIVE PRODUCTS: INACTIVATION KINETICS

ABSTRACT

A comprehensive experimental study of the drying of enzymes (E) and gin seng (GS) biomateriaJs provides a basis for mathematical modelling of the drying process with respect to the inactivation kinetics. Temperature of 20 - 120 °C was established for a number of enzymes while removing moisture with no thermal destruction. The kinetic parameters of inactivation were obtained for dry and wet enzymes and gin seng biomatenals. The software for kinetic parameters calculations for drying and inactivation of enzymes and gin seng biomateriaJs was drawn up, tested and verified experimentally. Methods of drying, design of dryers and regimes of drying of pure enzymes and gin seng biomaterials with minimum loss of bioactivity are suggested on the basis of model analysis and experimental data.     

SHRINKAGE OF APPLE DISKS DURING DRYING BY WARM AIR CONVECTION AND FREEZE DRYING

ABSTRACT

Volumetric and thickness shrinkage evaluated by direct measurement and n-heptane displacement were determined during convective and freeze drying of Golden delicious apples. For convective drying, the influence of blanching and diameter/thickness ratio of the apple disks used were analysed at different levels of moisture content under constant conditions. It was found that shrinkage of dried samples, both by convection and by freeze-drying, is anisotropic to a level which depends on sample geometry (ratio diameter/thickness) used. Blanching did not affect shrinkage results.

Based on results obtained a new model to predict bulk density of materials during drying is proposed, showing a better fit to experimental data than previous models reported in the literature. This model was further used to predict changes in apple porosity during drying.     

Quality Evaluation of Microwave-Dried Packham's Triumph Pear

Abstract

The objectives of this work were to carry out the microwave and microwave-convective drying of pear, in order to preserve the quality by reducing the drying time of the fruit; to compare the kinetic with convective drying mode data and to fit the comparative data to models from literature. The effect of osmotic dehydration and the variation in the microwave power were analyzed at constant values of air temperature and velocity. The experimental data fit well the proposed kinetic model. The processed pear was evaluated with respect to water content, quantity of calcium, phosphorus and potassium, water activity and apparent density. The best results were found for the samples osmotically dehydrated and dried in the microwave-convective dryer. The osmotic dehydration and the short drying times were important to maintain sample characteristics.     

Effect of outlet drying temperature and milk fat content on the physicochemical characteristics of spray-dried camel milk powder

Abstract

A composite face-centered experimental design was used to investigate the influence of spray drying conditions on the physicochemical characteristics of camel and cow milk powders. Response surface methodology (RSM) was deployed to appraise the effects of these processing parameters (the outlet drying temperature and the milk fat content) on water activity (a_w), glass transition temperature (T_g), bulk density, and free fat quantity. According to RSM analysis, it was noticed that the a_w and the T_g were primarily influenced by the outlet drying temperature instead of by milk fat content. Our results highlighted the negative effects of milk fat content and of the outlet drying temperature on the bulk density as well as on the free fat quantity of camel milk powder. Likewise, our findings underlined the negative effect of the outlet drying temperature on the bulk density of cow milk powder. However, the increase of fat content has led to the overexposure of fat at the free surface of the cow milk powder. Our results suggested a marked similarity of the overall thermodynamic behavior of both milks, during drying. Nevertheless, some differences were highlighted regarding the structuring of the particles of camel milk powder.     

Intergranular Air Movement and Grain Drying in Silos with Fully,Partially and Slanted Perforated Floor

ABSTRACT

Intergranular air movement and its relation with moving drying fmnt in a grain bulk were investigated experimentally. An improved computer simulation model was developed to analyze the drying or cooling process in a bed of grain with non-parallel airflow from a partially or slanted perforated floor. The model first simulates the airflow, then calc lates the heat and mass transfer between air and grain along the airflow streamlines. The results were compared with the simulated and experimental results from a fully perforated floor configuration. The degree of agreement between the computed and the experimental moisture contents depended upon the floor configuration. The model was not capable of predicting the temperatures to the accuracy of the predicted moisture contents, especially when airflow stream lines were not parallel to each other. For further improvement of the drying simulation model, an improved airflow model and computer program is required. Comparison of the simulated results with experimental data also     

DYNAMIC SHRINKAGE AND VARIABLE PARAMETERS IN BAKKER-ARKEMA'S MATHEMATICAL SIMULATION OF WHEAT AND CANOLA DRYING

Abstract

The bulk volume shrinkage was linearly related to instantaneous grain moisture reduction. The shrinkage coefficient was found to be primarily a function of air relative humidity. The Bakker-Arkema's bulk grain drying model was modified to incorporate the shrinkage equation. A correction factor for thin layer drying equation was also introduced to reduce deviation between the experimental and simulated moisture content. The Bakker-Arkema model showed significant improvement due to these modifications.     

Modeling of Drying Curves for Some Foodstuffs Using a Kinetic Equation of High Order

ABSTRACT

Non-linear regression was used to fit a high order kinetic model to drying curves for mango and cassava. For comparison purposes, the same experimental data were also adjusted by non-lines regression to a model based on exponential series, and to another exponential model by simple linear regression. The high order model fit the experimental data with higher precision (r2 Al.98) than the other exponential series models. The proposed higher order model is mathematically simple as compared to the exponential series, and could be used for simulation of drying processes.     

A fractional kinetic model for drying of cement-based porous materials

In this work, we attempt to characterize the drying phenomena of cement-based porous materials (CBPMs) using a fractional kinetic model that is represented by a function for the kinetics of complex systems and characterized by a stretched exponential and/or power-law function with two parameters: the order index n and the fractional time index α. The fractional kinetic model recovers the classic Lewis and Page drying models as well as the pseudo first-order and pseudo second-order adsorption/desorption models with appropriate n and α values and boundary conditions. The fractional kinetic and classic drying models (i.e., the Lewis, Henderson and Pabis, Page, and logarithmic models) were used to interpret the experimental drying data for cement pastes and mortars. Rearrangement of the fractional kinetic correlation generates a linear log ?log plot. The results showed that the values obtained using the fractional kinetic model and Page models were in better agreement with the experimental data than the values obtained using the other selected models. The results may also suggest that drying of CBPMs is more than a diffusion-controlled process.     

COMPARISON OF DIFFERENT DRYING KINETICS MODELS FOR SINGLE PARTICLES

ABSTRACT

Different kinetic drying models applied to non-shrinking materials are scrutinised and compared. Rigorous mechanistic models are difficult to apply because of the large number of unknown parameters; hence simpler alternatives have been applied instead. This paper focuses on the two most commonly used kinetic models, namely; the diffusion model and the characteristic drying curves. These were compared by plotting the predicted drying curves (moisture content versus time) in the same diagram as a reference curve. The response to different changes in drying conditions and sensibility to extrapolated conditions were tested. The parameters studied were the temperature, velocity and humidity of the gas and the size and initial moisture content of the panicles. The comparison was based on two approaches; one theoretical where the reference drying curves were generated by an rigorous drying model; and one experimental where the reference drying curves were measured using a thin-layer kinetics rig. The materials under study were softwood, ceramic clay, silica gel and purolit. The results were promising in the sense that the characteristic drying curves (CDCs) and diffusion model could both predict the response to most changes in external conditions. The predictions for drying above the boiling point were however less accurate than the ones below it, probably due to internal overpressure effects.     

Color Change Kinetics of Okra Undergoing Microwave Drying

In this present study, the effect of microwave output power and sample amount on color change kinetics of Turkey okra (Hibiscus esculenta L.) were investigated by using microwave drying technique. The color parameters for the color change of the materials were quantified by Hunter L (whiteness/darkness), a (redness/greenness), and b (yellowness/blueness) values. These values were also used for calculation of the total color change (ΔE), chroma, hue angle and browning index. The microwave drying process changed color parameters of L, a, and b, causing a color shift toward the darker region. The values of L and b decreased, whereas values of a and total color change (ΔE) increased during microwave drying. The mathematical modeling study of color change kinetics showed that L and b fit a first-order kinetic model, whereas a and total color change (ΔE) followed a zero-order kinetic model. However, chroma and browning index (BI) followed a first-order kinetic model, whereas hue angle followed a zero-order kinetic model. On the other hand, the data of the total color change (ΔE), chroma, hue angle, and browning index depending on the ratio of the microwave output power to sample amount were adequately fitted to a quadratic model. For calculation of the activation energy for color change kinetics parameters, the exponential expression based on Arrhenius equation was used.     

EFFECT OF DRYING METHOD ON SHRINKAGE AND POROSITY

The effect of drying method on bulk density, particle density, specific volume and porosity of banana, apple, carrot and potato at various moisture contents was investigated, using a large set of experimental measurements. Samples were dehydrated with five different drying methods: conventional, vacuum, microwave, freeze and osmotic drying. A simple mathematical model was used In order to correlate the above properties with the material moisture content. Four parameters with physical meaning were incorporated in the model: the enclosed water density p_w, the dry solid density p_s, the dry solid bulk density p_bo and the volume shrinkage coefficient β'. The effect of drying method on the examined properties was taken into account through its effect on the corresponding parameters. Only, dry solid bulk density was dependent on both material and drying method. Freeze dried materials developed the highest porosity, whereas the lowest one was obtained using conventional air drying.     

Prediction of Final Product Properties After Cocurrent Spray Drying

Abstract

The effect of drying and atomization conditions on the physical properties of powders for agglomerate-like materials and skin-forming material are studied in this article. A neural model is used for powder bulk and tapped density predictions.     

A NEW MODEL FOR SINGLE-LAYER DRYING

ABSTRACT

This paper presents a new empirical model for single layer drying process, which was verified with selected experimental data. The present model is also compared with other single layer drying models available in the literature, using laboratory as well as field data from literature.     

THE DEHYDRATION OF GARLIC. 1.DESORPTION ISOTHERMS AND MODELLING OF DRYING KINETICS

Abstract

Desorption isotherms for 1 mm thick garlic slices were determined at between 25 and 50°C and satisfactorily fitted with the G.A.B. equation. The kinetics of drying of slices of thickness 1.5 - 5.0 mm were determined at between 40 and 60°C using an air flow rate of 2.5 m-s^?, and the conditions affording a high-quality product m the shortest time were identified. After establishing how the effective diffusion coefficient of the garlic slices varied with their moisture content during drying, a diffusional model accounting for these variations was developed and satisfactorily fitted to the experimental kinetic data.     

Impact of Pulsed Electric Fields on the Dehydration and Physical Properties of Apple and Potato Slices

Abstract

The effect of pulsed electric fields (PEF) on drying and some physical properties of apple and potato was evaluated. Pulsed electric field intensities from 0.75 to 1.5 kV/cm with pulse duration within 100 and 300 μs were studied. The number of pulses applied was up to 120. Measurement of porosity and density were conducted using a mercury porosimeter. The drying process was carried out in a convective air oven at 70°C. The compressive strength of apples was reduced between 21 and 47% after treatment. The results show potential advantage for PEF enhanced juice extraction from the tissues even at moderate PEF treatment. PEF treatment increased porosity and particle density but decreased bulk density. Treating the apple samples with PEF resulted in generation of more pores of sizes in the order of cell wall thickness. Thus electric field application affected not only cell membranes but also cell wall integrity. PEF treatment enhanced drying rates of potato samples. Diffusion coefficients of PEF pretreated potato samples increased by up to 40%.     

MODELING OF ROUGH RICE DRYING IN THIN VERTICAL COLUMNS

ABSTRACT

The solution of classical diffusion equation based on the assumption of average moisture diffusion coefficient did not adequately represent natural convection drying of rough rice in thin vertical columns exposed on both sides to hot air. Instantaneous moisture diffusivity coefficients determined from experimental drying curves decreased continuously with an increase in exposure duration and were linearly related to moisture ratio. The proponionality constant which was called apparent moisture diffusion coefficient was distinctly related to air temperature, relative humidity, and initial moisture content of rough rice. The modified moisture diffusion model using the instantaneous moisture diffusion coefficient was found to best represent the moisture removal from bulk rough rice.