Use of hyperspectral imaging for the prediction of moisture content and chromaticity of raw and pretreated apple slices during convection drying

The feasibility of using spectral reflectance information in the visible—near infrared (400–1,000?nm) region to estimate moisture content (g_W/g_DM) and chromaticity (CIELAB) of apple slices was investigated during convection drying. Apple slices were pretreated with hot water blanching (50 and 70°C), acid application (citric and ascorbic), and combinations thereof before drying at 50 and 70°C. Prediction models for the space-averaged spectral reflectance curves were built using the partial least square regression method. A three-component partial least square regression (PLSR) model satisfied the minimal root mean square error (RMSE) criterion for predicting moisture content (avg. RMSEP?=?0.13, r²?=?0.99); importantly, the critical wavelengths remained the same across all pretreatments (540, 817, 977?nm). Similarly, PLSR modeling showed that the optimal set of wavelengths (in terms of RMSE) were invariant across pretreatment for CIELAB a* prediction (543, 966?nm) and CIELAB b* prediction (510, 664, 714, 914, 969?nm). The stability of the information content of these wavelengths across pretreatments indicates their independence of color changes. Additionally, the spatial information in the hyperspectral images was exploited to visualize the performance of the predictive models by pseudo-coloring their values for each pixel in a single apple slice across different drying times. This visualization of spatial distribution of predicted moisture content and chromaticity changes shows significant potential for use in online monitoring of the drying process.     

Aspergillus niger inactivation in microwave rotary drum drying of whole garlic bulbs and effect on quality of dried garlic powder

Abstract

Microwave rotary drum drying of whole garlic bulbs was investigated for the Aspergillus niger inactivation and moisture removal. The Weibull and Bigelow models were applied to microbial inactivation data. Garlic bulbs with initial moisture content in the range 1.95–2.14?g water g^?1?dry matter were dried up to 0.06?g water g^?1?dry matter. The microwave power density (PD) was varied from 1.03 to 2.67 Wg^?1 at 1.5 and 2.0 pulsation ratios (PRs). Effect of PD and PR on A. niger inactivation, product temperature, moisture diffusivity, moisture ratio, drying rate, color, and sensory parameters was studied. Page model was found to be a better fit for microwave rotary drying characteristics of whole garlic bulbs. Microwave rotary drum drying resulted in the average log reduction of A. niger between 1.12 and 1.60. Weibull model predicted A. niger inactivation better than the Bigelow model as it considered the nonlinearity associated with a microbial population in the sterilization process. Garlic powder prepared at 2.0 PR and 1.85 Wg^?1 PD was chosen as the best process based on sensory score. The cracking and peeling of garlic cloves were observed during microwave rotary drum drying. The SEM images confirmed the increase in the pore size of the microwave treated garlic sample than the untreated garlic which might be the reason for cracking and loosening of peel in garlic.     

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.     

Characterization of isotherms and thin-layer drying of red kidney beans,Part II: Three-dimensional finite element models to estimate transient mass and heat transfer coefficients and water diffusivity

Three-dimensional finite element models with consideration of shrinkage and irregular shape were developed to estimate the relationships among the transient heat and mass transfer coefficients, the transient water diffusivity, and the temperature and moisture content of the red kidney beans being dried under different drying conditions. An equation was developed to calculate the transient mass transfer coefficient using the measured time–moisture content data. This calculated transient mass transfer coefficient was further used to calculate the transient heat transfer coefficient. To verify the predicted temperature on the surface of the red kidney beans, surface temperature was measured using a handhold infrared thermometer. These measured temperature and time–moisture content data were used to determine the transient water diffusivity using the least square method when the red kidney bean kernel experienced a shrinkage during drying. Strong relationship among the transient heat and mass transfer coefficients, the water diffusivity, and the ratio of the transient heat and mass transfer coefficients was revealed. This relationship could be used to predict temperature and moisture content of the red kidney beans during the entire drying period. The Lewis number?=?27, and the ratio of the transient heat over mass transfer coefficients was 10765?J?m^?3?k^?1 at 30 and 40°C, and 10729?J?m^?3?k^?1 at 50°C. Shrinkage did not significantly influence the value of the estimated transient water diffusivity.     

A Model of Drying Kinetics of Acacia mangium Wood at Different Temperatures

The objective of this study was to determine the isothermal drying kinetics of Acacia mangium wood blocks by employing a relative humidity-controlled drying chamber. A model was developed based on solution of Fick's second law and evaluated through the coefficient of determination (R ² ), sum of square error (SSE), root mean square error (RMSE), and reduced chi-square (χ ² ). This model was compared to semi-theoretical models which are commonly used to describe the drying behavior of biomass in previous studies. The porosity and shrinkage characteristics of dried specimens were also evaluated. Based on the findings in this work, it was determined that the proposed model resulted in an excellent fit with experimental data for all four drying temperature levels of 30, 35, 40, and 45 ^° C to describe the isothermal drying kinetics of Acacia mangium . It appears that volumetric shrinkage of the samples decreased quadratically with decreasing moisture ratio. The activation energy of the drying process was determined to be 41.07 kJ/mol.     

Dielectric Properties and Optimization of Parameters for Microwave Drying of Petroleum Coke Using Response Surface Methodology

The dielectric properties of petroleum coke at five temperatures between 20 to 100 ^° C, covering different moisture content levels at 2.45 GHz, were measured using an open-ended coaxial probe dielectric measurement system. The effects of drying temperature, duration of drying, and sample mass on the moisture content and dehydration rate of petroleum coke was assessed utilizing the response surface methodology. The dielectric constant, loss factor, and loss tangent were all found to increase nearly linearly with increase in moisture content. Three predictive empirical models were developed to relate the dielectric constant, loss factor, and loss tangent of petroleum coke as a linear function of moisture content from 3–10%. An increase in temperature between 20 to 100 ^° C was found to increase the dielectric properties. The penetration depth was observed to increase linearly with decrease in moisture content in the range of 3 to 10%. A predictive empirical model was developed to calculate penetration depth for petroleum coke. Two mathematical models were established and analyzed using RSM to describe the relationship between the microwave drying conditions and the responses, moisture content, and dehydration rate. Statistical analysis with response surface regression showed that microwave drying temperature, duration of drying, and sample mass were significantly related to moisture content and dehydration rate. Based on the RSM analysis, the optimum process conditions were estimated to be a microwave drying temperature of 75 ^° C, drying duration of 10 sec, and sample mass of 60 g, with the resultant moisture content being 0.34 at a dehydration rate of 2.94 g/min.     

Study on quality attributes and drying kinetics of instant parboiled rice fortified with turmeric using hot air and microwave-assisted hot air drying

Abstract

This study investigated the quality and drying kinetics of instant parboiled rice fortified with turmeric (IPRFT) by using hot air (HA) and microwave-assisted hot air (MWHA) drying. The cooked long grain parboiled rice (LGPR) fortified with turmeric was dried with HA at temperatures of 65, 80, 95, and 110?°C. The microwave power density of 0.588 Wg^?1 was incorporated for drying with MWHA. Drying was performed until the dried IPRFT reached 16% (d.b.) of moisture content. The quality of the dried IPRFT was evaluated in terms of color, total phenolics content (TPC), total antioxidant capacity (TAC), rehydration ratio, volume expansion ratio, texture and microstructure. The results showed that the incorporation of microwave power with HA drying helped to reduce the drying time by 50% compared to conventional HA drying. A prediction of the moisture ratio by using the Page model provided the best R² and RMSE in drying kinetics. The drying conditions had small effects on the color, TPC, TAC, and microstructure of the dried IPFRT. The rehydration ratio, volume expansion ratio and texture of the rehydrated IPFRT showed minimal variations from changes in the drying conditions. The TPC and TAC of the dried IPRFT clearly increased compared to the TPC and TAC of the initial LGPR.     

Pulsed vacuum drying (PVD) of wolfberry: Drying kinetics and quality attributes

The effects of drying temperature (50, 53, 56, 59, 62, and 65°C) and pulsed vacuum ratio defined as the vacuum pressure duration versus atmosphere pressure duration (3:3, 6:6, 9:2, 12:5, 15:1, 18:4?min/min) on pulsed vacuum drying (PVD) characteristics and quality attributes of wolfberry in terms of polysaccharide content, color parameters (L^*, a^*, b^*, ΔE, and C), rehydration ratio and microstructure were investigated. Results revealed that appropriate PVD can reduce drying time by 73.2% compared to hot air drying at the same drying temperature. The moisture effective diffusivity (D_eff) ranged from 5.23?×?10^?10 to 9.73?×?10^?10?m²/s, calculated using the Weibull distribution model. The polysaccharide content, L^* (lightness), a^* (redness/greenness) of the PVD products were higher than those of the hot air-dried samples at the same drying temperature. The total color difference (ΔE) and color intensity (C) of PVD samples were close to those of the fresh ones. The retention rate of total polysaccharide content of PVD samples was about 49–77%, which was significantly higher than 30% of the hot air-dried samples. The surface of PVD wolfberry was highly porous, which may enhance moisture transfer during drying as well as rehydration processes. The results of current work indicate that PVD is a promising technology for wolfberry process, for the reason that PVD can reduce drying time significantly as well as enhance the quality attributes in terms of the total polysaccharide content, color parameters and rehydration ratio.     

Color prediction of mushroom slices during drying using Bayesian extreme learning machine

Abstract

Color is an important appearance attribute of fruits and vegetables during drying processing, as it influences consumer’s preference and acceptability. Establishing color change kinetics model is an effective way for better understanding the quality changes and optimization of drying process. However, it is difficult to quickly and accurately predict color change kinetics during drying as it is highly nonlinear, complex, dynamic, and multivariable. To alleviate this problem, a new model based on extreme learning machine integrated Bayesian methods (BELM) has been developed for the prediction of color changes of mushroom slices during drying process. The effects of drying temperature (55, 60, 65, 70, and 75?°C) and air velocity (3, 6, 9, and 12?m/s) on color change kinetics of mushroom slices during hot air impingement drying were firstly explored and the experimental results indicated that both drying temperature and air velocity significantly affected the color attributes. Then, to validate the robustness and effectiveness of BELM, the basic extreme learning machine (ELM) and traditional back-propagation neural network (BPNN) models have also been employed to predict the color quality. In terms of prediction accuracy and execution time, BELM could achieve least similar or even better performance than ELM and BPNN. It overcame the overfitting problems of ELM. The test results of optimal BELM model by two new cases revealed that the lowest R² and highest RMSE of BELM model were 0.9725 and 0.0563, respectively. The absolute values of relative errors between the actual and predicted values were lower than 8.5%.     

Modeling of combined far-infrared radiation and air drying of a ring shaped-pineapple with/without shrinkage

A ring shape is commonly used for industrial process of pineapple. Unfortunately, there has been no study on modeling of pineapple rings. Therefore we developed the mathematical model of pineapple rings during combined far-infrared radiation and air convection drying to investigate the evolutions of moisture content and qualities. The drying model based on the solution of Fick's law was used to estimate moisture diffusion coefficient (D). The D values with and without taking into account shrinkage phenomenon of dried products were compared. The kinetics of dried pineapple qualities such as color, shear force ratio and shrinkage during drying also were studied. Pineapples were pretreated, cut into rings and dried at far-infrared intensities of 1–5 kW/m² combined with air temperatures of 40–60 °C and air velocities of 0.5–1.5 m/s. The D values were found to increase with increasing intensity and air temperature. The D values with shrinkage consideration were lower than the D values without shrinkage consideration for all drying conditions. The quartic model gave a better fit over the other three polynomial models for describing the color kinetics. The thin layer drying models such as Page, Henderson and Pabis, Logarithmic and Midilli–Kucuk were modified in order to describe shear force ratio (SFR) of dried pineapple. The statistically analyses from this present study indicated that modification of drying models can be used to describe the kinetics of SFR and Midilli–Kucuk's form gave a better fit over the other form. The quadratic model was better than the linear model to predict shrinkage kinetics for all four dimensions (outer radius, inner radius, thickness and volume) of pineapple rings.     

The shrinkage properties of red pine wood assessed by image analysis and near-infrared spectroscopy

This work focused on the shrinkage and drying stress of red pine (Pinus densiflora) wood during kiln drying and investigated transverse shrinkage and moisture changes in thin specimens using digital image analysis and near-infrared spectroscopy, respectively. The effect of specimen thickness, which ranged from 1 to 10?mm on shrinkage, was analyzed under drying conditions with restrained stresses. The shrinkage due to moisture content was presented in the form of an exponential function and a linear function above and below the fiber saturation point, respectively. A shorter existence of the moisture gradient increased the transverse shrinkage. The tangential and radial shrinkage at the tissue level in 30-µm (longitudinal) thick slices was measured and compared with the shrinkage of above specimens with difference thicknesses. The transverse shrinkage of 1-mm-thick specimen is similar to the shrinkage measured using 30-µm-thick slice.     

Drying kinetics of poplar lumber during periodic hot-press drying

The drying kinetics of poplar lumber was experimentally investigated as a function of drying temperature (115, 135, 160, 185 and 205°C) during a periodic hot-press-drying process. Poplar lumber was dried under contact (compression ratio of 10%) and high-press states (compression ratio of 44%). Compared with the contact-state, the high-press-state showed higher drying rate and higher efficiency of removing free water than bound water in wood. Eight mathematical models from the literature were established to analyze the drying behavior. The Weibull model, with an average determination coefficient R² of 0.9958, fitted well for all applied drying conditions. The scale parameter decreased with increasing drying temperature and was lower for high-press-state drying compared with that for contact-state drying. Moisture diffusivity and activation energy were calculated according to the Weibull model. Diffusivity increased with increasing drying temperature, with the average value of 1.734?×?10^?6 and 3.313?×?10^?6?m²/s and activation energy of 34.79 and 32.85?kJ/mol for contact-state drying and high-press-state drying, respectively. Hot-press drying created an M-shaped curve of density distribution, with high density at the two surface regions gradually decreasing toward the core region. The contact state-dried wood showed increased density near the wood surface. Both average density and peak density improved in the case of high-press-state-dried wood. Furthermore, the hydrophilic index of wood for high-press-state drying was lower than that of the contact-state drying, and the opposite was true regarding crystallinity index. The hygroscopicity of high-press-dried poplar decreased with lower equilibrium moisture content and higher moisture excluding efficiency, compared with contact-state-dried poplar. The rapid, high-quality drying of poplar lumber through periodic hot-press was more potentially achieved by the high-press-state compared with contact-state drying.     

A Method of Determination of Concentration Dependent Effective Moisture Diffusivity

ABSTRACT

A method based on Fourier series solution to Fick's diffusion equation has been proposed to evaluate effective diffusivity (D) as a function of moisture content in agricultural materials undergoing shrinkage during drying process. The shrinkage kinetics of the particulate was used to correlate its instantaneous size (spherical equivalent diameter) as a function of material moisture content A computer program was used to evaluate D based on shrinkage kinetics and experimental drying data and relate it to moisture content. The method was used to obtain moisture diffusivity data for thin layer drying of grape and corn.     

DIFFUSIONAL MODEL WITH AND WITHOUT SHRINKAGE DURING SALTED FISH MUSCLE DRYING

Abstract

The drying process of salted pieces of shark muscle (Carckarhinus limbatus) was accomplished using three air conditions (20 ^°C -40 %RH; 30 ^°C - 30 %RH; 40 ^°C - 45 %RH) and two air velocities (0.5 m/s; 3.0 m/s). Shrinkage of material during drying was correlated as a linear function between linear dimension and moisture content. The experimental drying data were obtained using both the diffusional model with moisture content parameter (considering no shrinkage) and the diffusional model with moisture concentration parameter (considering shrinkage). The values of effective diffusivity varied between 1.50×l0^?10m²/s and 2 85×l0^?10m²/s for drying process considering no shrinkage and between 0.87×l0^?10m²/s and 1.61×l0^?10m²/s for process considering shrinkage. The activation energy was calculated assuming an Arrhenius' type equation. The values were 17.94 KJ/mol with the air velocity of 0.5 m/s and 21.94 kJ/mol with the air velocity of 3,0 m/s for effective diffusivity without shrinkage. The values were 2.04 kJ/mol with the air velocity of 0.5 m/s and 16.12 kJ/mol with the air velocity of 3.0 m/s for effective diffusivity with shrinkage. These low activation energy values, calculated considering the shrinking effect, show that the side effects during drying reduces the effective diffusivity dependence on temperature     

SHRINKAGE OF STRAWBERRIES DURING MICROWAVE DRYING

ABSTRACT

Strawberries were pretreated with ethyl oleate and sodium hydroxide solution to make the skin transparent to moisture diffusion. The treated berries were dried with convective air at 45°C and microwaves at two power levels of 0.1 and 0.2 W/g. During the drying process change in shrinkage ratio with respect to moisture ratio was studied. Also, the change in equivalent diameter of strawberries in correlation with moisture ratio was investigated. During drying the variation in surface and centre temperatures with moisture content and time was studied. It was observed that there is a direct relation between the shrinkage and moisture ratio. The equivalent diameter of the berry has a logarithmic function with respect to the moisture ratio.     

DIFFUSION MODELS OF PAPAYA AND MANGO GLACe’ DRYING

ABSTRACT

The objective of this research was to develop diffusion models for papaya and mango glace’ drying. Effective diffusion coefficients of papaya and mango glace’ were evaluated by regression analysis of the experimental data to drying kinetic equation. Models 1 and 2 were developed by assuming that effective diffusion coefficients were constant and varied proportionally with the moisture ratio. Model 3, which the Arrhenius factor was a second-degree polynomial function of moisture content, was developed by assuming that the value of effective diffusion coefficient was constant over a short time interval. Model 4, which was similar to Model 3, was developed by considering the effect of volume shrinkage during drying. Four diffusion models were compared and it was found that the predicted values of moisture contents calculated by using Models 1 and 2 were close to experimental values during the early period of drying. Models 3 and 4 were able to have better predictions particularly towards the final period of drying. However, Model 4 was complicated. Therefore, Model 3 was recommended for calculating drying curves of papaya and mango glace’ drying.     

DETERMINATION OF CROSS-GRAIN PROPERTIES OF CLEARWOOD SAMPLES UNDER KILN-DRYING CONDITIONS AT TEMPERATURE UP TO 140° C

ABSTRACT

Small specimens of Pinus radiata have been tested to determine the creep strain that occurs during the kiln drying of boards. The samples have been tested over a range of temperatures from 20°C to 140°C. The samples, measuring 150 × 50 × 5 mm, were conditioned at various relative humidities in a pilot-plant kiln, in which the experiments at constant moisture content (MC) in the range of 5-20% MC were undertaken to eliminate mechano-sorptive strains. To determine the creep strain, the samples were brought to their equilibrium moisture content (EMC), then mechanically loaded under tension in the direction perpendicular to the grain. The strain was measured using small linear position sensors (LPS) which detect any elongation or shrinkage in the sample. The instantaneous compliance was measured within 60 sec of the application of the load (stress). The subsequent creep was monitored by the continued logging of strain data from the LPS units.

The results of these experiments are consistent with previous studies of Wu and Milota (1995) on Douglas-fir ( Pseudotsuga menziesii ). An increase in temperature or moisture content causes a rise in the creep straw while the sample is under tension. Values for the instantaneous compliance range from 1.7 × 10^?3 to 1.28 × 10^?7 MPa^?1 at temperatures between 20°C and 140°C and moisture content in the range of 5-20%. The rates of change of the creep strains are in the Order of magnitude 10^?7to10^?8s^?1 for these temperatures and moisture contents. The experimental data have been fitted to the constitutive equations of Wu and Miloia (1996) for Douglas-fir to give material parameters for the instantaneous and Creep strain components for Pinus radiata.     

Kiln-, Solar-, and Air-Drying Behavior of Lumber of Tectona grandis and Gmelina arborea from Fast-Grown Plantations: Moisture Content,Wood Color,and Drying Defects

Tectona grandis and Gmelina arborea are common in commercial reforestation in the tropics. However, color variations, moisture content, and drying defects are also present in dried lumber. Moisture content variations, drying defects, and color changes were evaluated in the present work for three drying methods (kiln, solar, and air drying) during three seasons (dry, rainy, and transition season) in Costa Rica. According to the results, kiln drying had the fastest drying times, regardless of the season. On the other hand, air drying had slower drying time and higher final moisture content. With regard to defects, kiln drying produced the highest number and magnitude of defects in both species, whereas air drying showed the lowest quantity and severity of defects. No variations due to the drying methods or the season were observed in check and split, though solar drying presented intermediate values in all drying defects. The seasons of the year did not present any effect on drying defects. Finally, T. grandis dried lumber is darker than green lumber, and dried G. arborea wood is clearer. In addition, there is an increase in red ( a ^* ) and yellow ( L ^* ) tonalities, and color changes (Δ E ^* ) are considered perceptible or very perceptible in both species. No differences were found among the three drying methods in Δ E ^* , although the season of the year affected dif L ^* and dif C ^* significantly.     

A Simulation Tool for the Optimization of Lumber Drying Schedules

Abstract

A two-dimensional wood drying model based on the water potential concept is used to simulate the convection batch drying of lumber at conventional temperature. The model computes the average drying curve, the internal temperature and moisture content profiles, and the maximum effective moisture content gradient through board thickness. Various scenarios of conventional kiln-drying schedules are tested and their effects on drying time, maximum effective moisture content gradient, final moisture content distribution within and between boards, and energy consumption are analyzed. Simulations are performed for two softwood species, black spruce (Picea mariana (Mill.) B.S.P.) and balsam fir (Abies balsamea (L.) Mill.). The simulation results indicate that the predictive model can be a very useful tool to optimize kiln schedules in terms of drying time, energy consumption, and wood quality. Such a model could be readily combined with intelligent adaptive kiln controllers for on-line optimization of the drying schedules.     

Evaluating a Solar Dryer for In-Shell Drying of Split Pistachio Nuts

Abstract

A thin-layer forced air solar dryer was designed to study the feasibility of drying pistachio nuts. The dryer was tested during the 2001 and 2002 drying seasons. The maximum temperature in the solar collector reached 56°C, which was 20°C above the ambient temperature. The required drying time was 36 h. During the first day of drying (0800 to 1700 h) the moisture content dropped to about 21% (wb). The final moisture content of the dried nuts was 6% wb, which was 1% below the recommended storage moisture. The drying constant of the pistachio nuts during solar drying was determined using two mathematical models, a one-term series solution of Fick's diffusion equation and an exponential decaying model. There was no significant difference between the two models (α = 0.05). In general, the quality of solar dried nuts was better than the conventional heated air due to slower drying rates.