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.     

Microwave Heat Treatment of Spinach: Drying Kinetics and Effective Moisture Diffusivity

The effect of microwave drying technique on moisture content, moisture ratio, drying rate, drying time, effective moisture diffusivity, and porosity of spinach (Spinacia oleracea L.) were investigated. By increasing the microwave output powers (180–900 W) and the sample amounts (25–100 g), the drying time decreased from 18 to 3.5 min and increased from 7.7 to 25 min, respectively. To determine the kinetic parameters, the drying data were fitted to various models based on the ratios of the differences between the initial and final moisture contents and equilibrium moisture content versus drying time. Among of the models proposed, Page's model gave a better fit for all drying conditions applied. The activation energy was calculated using an exponential expression based on Arrhenius equation. The relationship between the drying rate constant and effective moisture diffusivity was also estimated and gave a linear relationship.     

Microwave Heat Treatment of Spinach: Drying Kinetics and Effective Moisture Diffusivity

The effect of microwave drying technique on moisture content, moisture ratio, drying rate, drying time, effective moisture diffusivity, and porosity of spinach (Spinacia oleracea L.) were investigated. By increasing the microwave output powers (180-900 W) and the sample amounts (25-100 g), the drying time decreased from 18 to 3.5 min and increased from 7.7 to 25 min, respectively. To determine the kinetic parameters, the drying data were fitted to various models based on the ratios of the differences between the initial and final moisture contents and equilibrium moisture content versus drying time. Among of the models proposed, Page's model gave a better fit for all drying conditions applied. The activation energy was calculated using an exponential expression based on Arrhenius equation. The relationship between the drying rate constant and effective moisture diffusivity was also estimated and gave a linear relationship.     

Color Change Kinetics of Spinach Undergoing Microwave Drying

In this present study, the effect of microwave output power and sample amount on color change kinetics of Turkey spinach (Spinacia oleracea L.) were investigated by using microwave drying technique. The color parameters for the color change of the materials were quantified by the Hunter L (whiteness/darkness), a (redness/greenness), and b (yellowness/blueness) system. 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, while values of a and total color change (ΔE) increased during microwave drying. The mathematical modeling study of color change kinetic showed that L and b fitted to a first-order kinetic model, while a and total color change (ΔE) followed by a zero-order kinetic model. However, chroma and browning index (BI) followed a first-order kinetic model, while hue angle followed a zero-order kinetic model. To illustrate the relationship of the L, a, b, total color change (ΔE), chroma, hue angle, and browning index depending on the ratio of the microwave output power to sample amount, the data adequately fitted to a quadratic (second order polynomial) model. For calculation of the activation energy for color change kinetic parameters, the exponential expression based on an Arrhenius equation was used.     

春笋微波干燥动力学模型研究

在不同微波功率下研究春笋（5mm厚度，200g）干燥过程中失水速率和颜色的变化规律。失水速率随微波功率增大而增大，用拟和性较好的Page方程建立了水分比变化模型。色泽变化参数用亮度L、红色度a和黄色度b表示。红色度a值和黄色度b值上升而亮度L下降，笋片微波干燥后总体色泽加深。色泽各参数变化用食品中零级和一级反应模型来拟和，其中L和b的变化适合一级反应模型，a的变化适合用零级反应模型表达。     

Moisture Diffusivity Analysis in a Microwave Drying Process under Different Operating Conditions

This article deals with the kinetic analysis of the drying of sliced mushrooms (Agaricus bisporous) and apples (Golden Delicious), as representatives of vegetables and fruits, by the application of microwave. The drying experiments were carried out in monomode or multimode cavities, depending on the purpose of the study. In the former, the location of the temperature control is analyzed, and in the latter, the effect of pressure, air humidity, and temperature control. In the experiments, the mass loss was monitored over time and the drying kinetics described by means of a model, assuming effective diffusivity to be constant. The changes in the diffusion coefficient could be explained in terms of possible texture modifications of the product derived from the different conditions experienced during drying.     

Moisture Diffusivity Analysis in a Microwave Drying Process under Different Operating Conditions

This article deals with the kinetic analysis of the drying of sliced mushrooms (Agaricus bisporous) and apples (Golden Delicious), as representatives of vegetables and fruits, by the application of microwave. The drying experiments were carried out in monomode or multimode cavities, depending on the purpose of the study. In the former, the location of the temperature control is analyzed, and in the latter, the effect of pressure, air humidity, and temperature control. In the experiments, the mass loss was monitored over time and the drying kinetics described by means of a model, assuming effective diffusivity to be constant. The changes in the diffusion coefficient could be explained in terms of possible texture modifications of the product derived from the different conditions experienced during drying.     

Effect of Microwave Energy on Vacuum Drying Kinetics of Alginate-Starch Gel

Microwave energy drying under vacuum was investigated for alginate-starch hydrogel. Drying was conducted using 2450 MHz microwave energy at 25 mm Hg absolute pressure and different power levels; e.g., 300, 500, 700, 900, and 1100 watts. Drying was continued until final moisture content of the sample reached less than 1% wet basis. Moisture loss during drying was measured at 3-min intervals. Drying kinetics were used to describe both macroscopic and microscopic mechanisms of heat and mass transfer. Experimental drying kinetic data were fitted to a mathematical model. Experimental drying data points were fitted to an empirical model equation.     

Effect of Microwave Energy on Vacuum Drying Kinetics of Alginate-Starch Gel

Microwave energy drying under vacuum was investigated for alginate-starch hydrogel. Drying was conducted using 2450 MHz microwave energy at 25 mm Hg absolute pressure and different power levels; e.g., 300, 500, 700, 900, and 1100 watts. Drying was continued until final moisture content of the sample reached less than 1% wet basis. Moisture loss during drying was measured at 3-min intervals. Drying kinetics were used to describe both macroscopic and microscopic mechanisms of heat and mass transfer. Experimental drying kinetic data were fitted to a mathematical model. Experimental drying data points were fitted to an empirical model equation.     

Estimation of Effective Moisture Diffusivity of Okra for Microwave Drying

The effect of microwave output power and sample amount on effective moisture diffusivity were investigated using microwave drying technique on round okra (Hibiscus esculentus L.). The various microwave output powers ranging from 180 to 900 W were used for the determination of effective moisture diffusivity for constant sample amount of 100 g okra. To examine the effect of sample amount on effective moisture diffusivity, the samples in the range of 25-100 g were dried at constant microwave output power of 360 W. By increasing the microwave output powers and decreasing the sample amounts, the effective moisture diffusivity values ranged from 20.52 × 10^-10 to 86.17 × 10^-10 and 34.87 × 10^-10 to 11.91 × 10^-9 m²/s^-1, respectively. The modeling studies were performed to illustrate the relationship between the ratio of the microwave output power to sample amount and effective moisture diffusivity. The relationship between drying constant and effective moisture diffusivity was also estimated.     

Estimation of Effective Moisture Diffusivity of Okra for Microwave Drying

The effect of microwave output power and sample amount on effective moisture diffusivity were investigated using microwave drying technique on round okra (Hibiscus esculentus L.). The various microwave output powers ranging from 180 to 900 W were used for the determination of effective moisture diffusivity for constant sample amount of 100 g okra. To examine the effect of sample amount on effective moisture diffusivity, the samples in the range of 25–100 g were dried at constant microwave output power of 360 W. By increasing the microwave output powers and decreasing the sample amounts, the effective moisture diffusivity values ranged from 20.52 × 10^?10 to 86.17 × 10^?10 and 34.87 × 10^?10 to 11.91 × 10^?9 m²/s^?1, respectively. The modeling studies were performed to illustrate the relationship between the ratio of the microwave output power to sample amount and effective moisture diffusivity. The relationship between drying constant and effective moisture diffusivity was also estimated.     

Experimental Study on Microwave Vacuum Drying of Two-Porosity Level Media

Microwave vacuum drying experiments were performed on a laboratory scale dryer with a two-level porosity material: a packed bed of porous alumina beads. The incident microwave power and the vacuum pressure level were fixed, the main varying parameters being the beads diameter and porosity, and the mean pore diameter. The drying kinetics and the evolution of the product temperature are presented. The drying kinetics can be divided into two main periods. The first one corresponds to the drying from the bed voids according to evaporation mechanism that we describe with a stagnant film law. The second one corresponds to the drying from the particle pores and we divide it into two parts: we suggest that the former is dominated by capillarity driven moisture transport, and the latter is limited by the desorption kinetics of the few water layers left.     

Experimental Study on Microwave Vacuum Drying of Two-Porosity Level Media

Abstract

Microwave vacuum drying experiments were performed on a laboratory scale dryer with a two-level porosity material: a packed bed of porous alumina beads. The incident microwave power and the vacuum pressure level were fixed, the main varying parameters being the beads diameter and porosity, and the mean pore diameter. The drying kinetics and the evolution of the product temperature are presented. The drying kinetics can be divided into two main periods. The first one corresponds to the drying from the bed voids according to evaporation mechanism that we describe with a stagnant film law. The second one corresponds to the drying from the particle pores and we divide it into two parts: we suggest that the former is dominated by capillarity driven moisture transport, and the latter is limited by the desorption kinetics of the few water layers left.     

Optimizing Drying Conditions for the Microwave Vacuum Drying of Enzymes

The aim of this study was the methodological use of experimental planning for the optimization of microwave vacuum drying of enzymes using α-amylase as a model. A factorial in star designwas used to optimize the microwave vacuum–drying process, and the variables were power output and vacuum pressure. The material dehydrated by this technique was analyzed with regard to its enzymatic activity, water activity, and moisture content. Response surface methodology was used to estimate the main effects of vacuum pressure and power on the enzymatic and water activities. The experimental in star design revealed that microwave vacuum drying is influenced mainly by power. The dehydrated product showed high enzymatic activity and low water activity.     

Microwave Energy Absorption Behavior of Foamed Berry Puree Under Microwave Drying Conditions

The microwave energy absorption behavior of foamed berry puree was studied considering the variations in the physical properties of the material. The absorptions of microwave energy within foamed berry puree indicated fluctuating trends in decay as microwave drying progressed, which were attributed to the effects of temperature, moisture content, and density of the material. Mathematical models of the dielectric constant ?′ and dielectric loss factor ?″ as a function of temperature and moisture content were developed using second-order functions. During microwave drying of foamed berry puree, moisture content had the most important negative influence on the dielectric constant and dielectric loss factor, followed by temperature and porosity.     

Drying of Diced Carrot in a Combined Microwave-Fluidized Bed Dryer

Drying of diced carrot (∼90% wet basis) was carried out in a laboratory microwave fluidized-bed dryer (MFB) and in a standard fluidized-bed dryer (FB). It was found that the drying time in the MFB dryer is 2-5 times shorter than in the FB dryer. Drying efficiency (DE) is a function of moisture content, microwave power and temperature of drying agent. Higher values of DE are obtained for MFB dryer. For both drying systems the water removal was proceeding in two-stage falling rate period (except short initial term).     

Microwave Freeze Drying of Sea Cucumber Coated with Nanoscale Silver

To develop an improved dehydration method for sea cucumber, microwave freeze drying was tested as a potential method. According to our experimental results, microwave freeze drying can reduce drying time to about half of the traditional vacuum freeze-drying process. To ensure a high degree of sterilization, a novel nanoscale silver coating technique was combined with microwave freeze drying. Microwave freeze drying combined with nanoscale silver coating treatment leads to a much lower microorganism number with no significant effect on drying efficiency and sensory quality.     

Microwave Freeze Drying of Sea Cucumber Coated with Nanoscale Silver

To develop an improved dehydration method for sea cucumber, microwave freeze drying was tested as a potential method. According to our experimental results, microwave freeze drying can reduce drying time to about half of the traditional vacuum freeze-drying process. To ensure a high degree of sterilization, a novel nanoscale silver coating technique was combined with microwave freeze drying. Microwave freeze drying combined with nanoscale silver coating treatment leads to a much lower microorganism number with no significant effect on drying efficiency and sensory quality.     

Microwave-Assisted Thin Layer Drying of Wheat

Drying characteristics of Canada Western Red Spring (CWRS) wheat were studied using a domestic microwave convective oven. The effects of microwave power level, grain bed thickness, and initial grain moisture on the drying kinetics were investigated. Wheat samples with initial moisture levels of 0.18 to 0.29 kg water/kg of dry matter were dried for different drying periods of 180 to 360 s. The moisture loss data were recorded at regular short intervals. Then moisture loss data were fitted to various models (Page equation, modified drying equation, and Midilli equation) to study the drying kinetics of wheat. The results showed that wheat moisture loss increased with increasing microwave power level. A mathematical model was developed by coupling mass and energy balances, resulting in a system of non-linear equations. The predicted moisture loss data from the developed model were compared by fitting to experimental microwave data that were in good agreement.     

Energy Efficiency and Drying Kinetics of Recycled Paper Pulp

In this work, the influences of the air temperature and velocity on the drying kinetics of recycled paper pulp were analyzed. The increase of both variables positively influences the process, concerning the final moisture content and the drying time. However, optical microscopy and visual observation showed worse quality of the paper for drying conditions of high air temperature and velocity, presenting less uniformity and overdried surfaces. The dryer energy efficiency was evaluated by performance parameters and the results were compared with the ones obtained for other types of industrial paper dryers, presenting good agreement.