Drying and quality characteristics of fresh and sugar-infused blueberries dried with infrared radiation heating

We evaluated the finished product quality and infrared (IR) drying characteristics of fresh and sugar-infused blueberries dried with a catalytic infrared (CIR) dryer. IR drying tests were conducted at four product temperatures (60, 70, 80, and 90 °C) to evaluate the drying rate and the color and texture of the finished product. Fresh blueberries dried with convective hot air drying at 60 °C were used as control for comparison. The experimental data of moisture changes during IR drying were modeled with eight different models, including Page, modified Page, Thompson, Newton, Wang and Singh, and Henderson and Pabis, and two models developed in this study. The Thompson model showed the best fit to all experimental data. The CIR drying produced firmer-texture products with much reduced drying time compared with hot air drying. For fresh blueberries, CIR drying conserved drying time by 44% at 60 °C. The effective moisture diffusivity ranged from 2.24 × 10⁻¹⁰ to 16.4 × 10⁻¹⁰ m²/s and from 0.61 × 10⁻¹⁰ to 3.84 × 10⁻¹⁰ m²/s for fresh and sugar-infused blueberries, respectively.     

Analysis of giant pumpkin (Cucurbita maxima) drying kinetics in various technologies of convective drying

The paper analyses the results of the research on drying a variety of giant pumpkin (Justynka – 957). The research involved drying kinetics of pumpkin as well as changes in the volume of 10 mm pumpkin cubes, dried at the temperature of 80 °C, using free (natural) convection and in the forced convection in the tunnel dryer, with the drying factor speed of 1.2 m s⁻¹ and in the fluid bed dryer. Drying kinetics of pumpkin pieces dried in the tunnel dryer, fluid bed dryer and during two-stage initial drying in the tunnel, and in the fluid bed dryer were examined. Measurements results were used to verify the theoretical models of drying kinetics of the first period taking volume shrinkage into consideration, and the second period of the examined processes.     

Vacuum drying kinetics of Asian white radish (Raphanus sativus L.) slices

In this study, radish slices were dried as single layers with thickness of 4 and 6 mm in the ranges of 40-60 °C of drying air temperature in a laboratory scale vacuum dryer. The effect of drying air temperature and slice thickness on the drying characteristics was determined. Moisture transfer from radish slices was described by applying the Fick's diffusion model, and the effective diffusivity changes between 6.92 × 10⁻⁹ and 14.59 × 10⁻⁹ m²/s within the given temperature range. Effective diffusivity increased with increasing temperature. An Arrhenius relation with activation energy values of 16.49 and 20.26 kJ/mol for the thickness of 4 and 6 mm expressed the effect of temperature and sample thickness on the diffusivity. A non-linear regression procedure was used to fit nine thin-layer drying models available in the literature to the experimental moisture loss data. The models were compared based on the coefficient of determination, mean relative percent deviation, root mean square error, and the reduced chi-square between the observed and predicted moisture ratios. The logarithmic model has shown a better fit to the experimental drying data as compared to other models.     

Kinetics and modeling of whole longan with combined infrared and hot air

The aim of this research was to evaluate the effects of operating variables on the drying behavior of whole longan undergoing a combined infrared and hot air drying process, to determine its kinetic parameters, and to develop drying kinetic models. The single-layer drying experiments were carried out at infrared powers of 300, 500 and 700 W, drying air temperatures of 40, 60 and 80 °C, and air velocities of 0.5, 1.0 and 1.5 m/s. The samples were dried until attaining a final moisture content of 0.2 kg water/kg dry solid. The results show that the drying had a short constant rate period followed by a falling rate period in all cases. The drying rate and product temperature were significantly influenced by infrared power, temperature and velocity of ambient air. In the constant rate period, the mass transfer coefficient varied from 3.646 × 10⁻³ to 1.914 × 10⁻² m/s. It increased with increasing infrared power, but decreased as air velocity and air temperature increased. In the falling rate period, theoretical and semi-empirical drying kinetic equations were used to describe the drying kinetics of the product. It was found that the overall effective diffusion coefficient and drying constant varied from 7.012 × 10⁻¹¹ to 6.681 × 10⁻¹⁰ m²/s and 0.026 to 0.234 h⁻¹, respectively. Both parameters increased with increasing infrared power and air temperature, but decreased with increasing air velocity. Combined regression equations developed to predict the drying kinetic parameters (h_D, D_eff and k) for all three models gave a fairly good fit.     

Moisture diffusivity of rough rice under infrared radiation drying

To design efficient infrared (IR) dryers for rough rice, it is important to understand the drying behavior of rough rice under IR heating. The objective of this study was to determine the moisture diffusivity of rough rice under IR heating followed by cooling. The effects of initial moisture content, rice temperature, drying bed thickness, tempering, and cooling methods on moisture diffusivity and moisture diffusivity coefficient were investigated. Samples of freshly harvested medium grain rice (M202 variety) with initial moisture content (MC) of 25.8, 31.2 and 33.8 g moisture/100 g dry solid were used. They were dried with IR radiation intensity of 5348 W/m², for six exposure times, 15, 30, 40, 60, 90 and 120 s. The tested drying bed thicknesses were single-layer, 5 mm and 10 mm. The unsteady diffusion equation based on Fick’s law and slope methods were used to describe moisture diffusivity. The results indicated that rough rice moisture diffusivities under IR heating and cooling were significantly affected by rice temperature and tempering treatment, respectively. High heating rate and moisture diffusivity were achieved with IR heating. It took only 60, 90 and 120 s to achieve about 60 °C rice temperature with corresponding moisture diffusivities of 4.8 × 10⁻⁹, 3.6 × 10 ⁻⁹ and 3.4 × 10⁻⁹ m²/s during heating for drying bed thicknesses of a single layer, 5 mm and 10 mm, respectively. The moisture diffusivity coefficients during heating and cooling of IR dried rice with tempering were much higher than those of convective drying, which reflected the high drying rate of the IR drying method.     

Effect of processing methods on the concentrations of bioactive components of ginseng (Panax ginseng C.A. Meyer) adventitious roots

Adventitious roots of Korean mountain ginseng (Panax ginseng C.A. Meyer) were processed by using forced air drying methodology at 30, 50 and 70 °C for 1, 3, 5, 10 and 20 h with objective of developing suitable processing/drying technique. Drying of adventitious roots at 50 °C for 10 h was found suitable as desirable moisture content (3.13 g water/dry matter i.e. 10%) could be reached with dried roots. Roots which were dried by such treatment were also possessing higher amount of ginsenosides (1.5 mg g⁻¹ DW triols, 15.9 mg g⁻¹ DW diols and 17.4 mg g⁻¹ DW of total ginsenosides) and phenolics. Adventitious roots were also processed by using far infrared and freeze drying methods and results revealed that forced air drying method is superior to far infrared and freeze drying methods.     

Drying description of cylindrical pieces of bananas in different temperatures using diffusion models

Three diffusion models were used to describe drying of bananas cut into cylindrical pieces. Analytical solutions of the diffusion equation with boundary conditions of the first and third kind were used to describe the process. In the drying experiments using hot air, the cylindrical pieces had the following dimensions: length of about 21 mm and radius of 15 mm, on average. The drying air temperatures were 40, 50, 60 and 70 °C. To determine the process parameters, an optimizer was coupled to the analytical solutions. For the best model, the effective mass diffusivities were 2.53 × 10⁻⁸; 3.12 × 10⁻⁸; 6.19 × 10⁻⁸ and 7.32 × 10⁻⁸ m² min⁻¹, while the convective mass transfer coefficients were 1.93 × 10⁻⁵; 3.04 × 10⁻⁵; 3.18 × 10⁻⁵ and 4.97 × 10⁻⁵ m min⁻¹. The determination coefficients were greater than 0.9990 and the chi-squares were less than 5.3 × 10⁻³ for all simulations of the experiments.     

Electrohydrodynamic (EHD) drying of tomato slices (Lycopersicon esculentum)

The drying rate of tomato slices (Early Urbana L.) treated by a high voltage electrostatic field (HVEF) was investigated with an oven-drying and open-room drying sample, under identical conditions. ANOVA showed that the drying methods had a significant effect (P ? 0.01) on decreasing moisture content, surface temperature, and apparent color of tomato slices, but no difference was observed in shrinkage. Average drying rate for 3, 4, and 5 kV cm⁻¹ electrostatic fields over a period of 780 min increased by 1.3, 1.43, and 2 times, respectively, compared to that of the air-dried. Tomato slices dried with EHD⁺, which consumed only 16.5 mJ g⁻¹ of electric power, exhibited a better appearance (lightness and red color) with lower surface temperature than the air-dried and oven drying samples.     

Osmotic dehydration of raspberries with vacuum pretreatment followed by microwave-vacuum drying

Defrozen raspberries were osmotically dehydrated in sucrose solution initially at low pressure (1.33 kPa for 8 min), and then at ambient pressure (4 h). Moisture decreased from 84% to 49% (wet basis), and almost one half of water removal occurred at the vacuum period. Two different transport coefficients were obtained: 19.9 × 10⁻¹⁰ m²/s for transport of water under vacuum, and 3.2 × 10⁻¹⁰ m²/s for water transport at atmospheric pressure. Losses of vitamin C were high (80%) and reutilization of sucrose solution is suggested. Osmotically dried raspberries were microwave-vacuum dried (1.33 kPa for 40 min) under on–off temperature control by varying microwave settings. An undamaged dried product (7.8% wet basis) of high quality (color, taste, structure) was obtained.     

Thin layer drying characteristics of rapeseed (Brassica napus L.)

This study was performed to determine the most appropriate thin layer drying model and the effective moisture diffusivity of rapeseed. The thin layer drying tests were conducted at three different combinations of drying air temperature levels of 40, 50, and 60 °C and relative humidity levels of 30, 45, and 60%. The thin layer drying characteristics of rapeseed were determined. The Page (1949) model was the most adequate model for describing the thin layer drying of rapeseed. Drying occurred in the falling rate period and the rate of moisture removal from rapeseed was governed by the rate of water diffusion to the surface of the seed. Effective moisture diffusivities were calculated based on the diffusion equation for a spherical shape using Fick’s second law. Effective moisture diffusivity during drying varied from 1.72 × 10⁻¹¹ to 3.31 × 10⁻¹¹ m² s⁻¹ over the temperature range. The dependence of moisture diffusivity on temperature was described by an Arrhenius-type equation. The activation energy for moisture diffusion during drying was 28.47 kJ mol⁻¹.     

Drying of yellow pea starch on inert carriers: Drying kinetics,moisture diffusivity,and product quality

This study aimed at investigating the drying of yellow pea starch dispersions on inert solid carriers and determining the drying kinetics, moisture diffusivity and the product quality, quantified through damage index and final moisture content. Drying kinetics accomplished in a convective drying tunnel show that the overall mass transfer is controlled by internal migration of moisture within the starch particles. For a given inlet air temperature from 100 to 180 °C, the apparent diffusion coefficient derived from the drying curves increases exponentially with the instantaneous moisture content, with values ranging from 4 × 10⁻¹¹ to 3 × 10⁻⁸ m²/s. Due to low diffusivity and the thin coat formed on the surface of solid carriers, the resistance to internal diffusion is negligible as compared to the overall mass transfer resistance when drying of starch dispersions takes place on inert solid carriers. Drying of yellow pea starch dispersion on Teflon particles as inert carriers was studied in laboratory and pilot fast spouted bed dryer for inlet air temperatures from 140 to 240 °C, and initial solid content of 38%, mass (d.b.). The starch damage index for targeted product moisture content was below 2.5% in the inlet air temperature range from 120 to 210 °C, when atomizing from the bottom of dryer.     

Effect of hot air drying and sun drying on color values and β-carotene content of apricot (Prunus armenica L.)

In this study, sulphurated and nonsulphurated Hacihaliloglu apricots (Prunus armenica L.) which is the most widely produced cultivar in Turkey were used to study the effects of different hot air drying temperatures (50, 60, 70, and 80 °C) and sun drying on color and β-carotene content of apricot. The time required to obtain the desired final dry matter in hot air drying was lower than sun drying. Sulphuration also decreased drying time at all drying conditions. Color values and β-carotene content of hot air dried samples were favorable in comparison to air drying. β-carotene content in dried apricots at 70 and 80 °C was 7.14, 7.17 mg 100 g⁻¹ dry matter and 6.12, 6.48 mg 100 g⁻¹ dry matter for sulphurated and nonsulphurated apricots, respectively. A good relationship was found between treatments (drying temperatures and drying times) and β-carotene content for sulphurated and nonsulphurated apricots (R²=0.9422 and 0.9129, respectively).     

Mathematical model of pork slice drying using superheated steam

Superheated steam has received much attention as an effective technique for drying purposes because it produces dried products with high quality attributes. Although currently there are a number of works reporting the development of a mathematical model of superheated steam drying, they do not use a numerical method to estimate the effective moisture diffusivity value (D_eff value) of the product. The purposes of this work, therefore, were to develop a semi-empirical model for estimating the D_eff value of pork, and for predicting the evolution of the moisture content and the center temperature of sliced pork during superheated steam drying. The model was based on mass and energy-balance equations and was divided into three periods: heating up, constant drying rate and falling drying rate period. It was solved using an explicit finite difference method and used a grid search method to estimate the D_eff value of pork. The predicted results were compared with the experimental data of superheated steam drying of seasoned and unseasoned pork with slice thicknesses of 1 and 2 mm at a drying temperature of 140 °C. The comparison results showed that the developed model could estimate the ranges of the D_eff value of pork fairly well (D_eff = 3.311-12.471 × 10⁻¹⁰ m²/s for seasoned pork, and 4.200-15.056 × 10⁻¹⁰ m²/s for unseasoned pork) and could reasonably predict the evolution of the moisture content of the sliced pork. The predicted center temperature of the sliced pork was higher than the experimental data in the heating up period and in the first 5 min of the falling drying rate period, but it agreed well in the constant drying rate period and after the drying time of 10 min. Moreover, it was found that the slice thickness and the seasoning had an influence on the drying curves only in the constant drying rate and falling drying rate period.     

Chemical composition of cultivated seaweed Ulva clathrata (Roth) C. Agardh

Samples of cultivated Ulva clathrata were collected from a medium scale system (MSS, 1.5 × 1.5 m tank), or from a large scale system (LSS, 0.8 ha earthen pond). MSS samples were dried directly while the LSS sample was washed in freshwater and pressed before drying. Crude protein content ranged 20–26%, essential amino acids accounting for 32–36% of crude protein. The main analysed monosaccharides were rhamnose (36–40%), uronic acids (27–29%), xylose (10–13%) and glucose (10–16%). Some notable variations between MSS and LSS samples were observed for total dietary fibre (26% vs 41%), saturated fatty acids (31% vs 51%), PUFAS (33% vs 13%), carotenoids (358 vs 169 mg kg⁻¹ dw) and for Ca (9 vs 19 g kg⁻¹), Fe (0.6 vs 4.2 g kg⁻¹), Cu (44 vs 14 mg kg⁻¹), Zn (93 vs 17 mg kg⁻¹) and As (2 vs 9 mg kg⁻¹). The chemical composition of U. clathrata indicates that it has a good potential for its use in human and animal food.     

Effect of drying methods on the physical properties and microstructures of mango (Philippine ‘Carabao’ var.) powder

Mango powders were obtained at water content below 0.05 kg water/kg dry solids using Refractance Window® (RW) drying, freeze drying (FD), drum drying (DD), and spray drying (SD). The spray-dried powder was produced with the aid of maltodextrin (DE = 10). The chosen drying methods provided wide variations in residence time, from seconds (in SD) to over 30 h (in FD), and in product temperatures, from 20 °C (in FD) to 105 °C (in DD). The colors of RW-dried mango powder and reconstituted mango puree were comparable to the freeze-dried products, but were significantly different from drum-dried (darker), and spray-dried (lighter) counterparts. The bulk densities of drum and RW-dried mango powders were higher than freeze-dried and spray-dried powders. There were no significant differences (P ? 0.05) between RW and freeze-dried powders in terms of solubility and hygroscopicity. The glass transition temperature of RW-, freeze-, drum- and spray-dried mango powders were not significantly different (P ? 0.05). The dried powders exhibited amorphous structures as evidenced by the X-ray diffractograms. The microstructure of RW-dried mango powder was smooth and flaky with uniform thickness. Particles of freeze-dried mango powder were more porous compared to the other three products. Drum-dried material exhibited irregular morphology with sharp edges, while spray-dried mango powder had a spherical shape. The study concludes that RW drying can produce mango powder with quality comparable to that obtained via freeze drying, and better than the drum and spray-dried mango powders.     

Utility of solid phase spectrophotometry for the modified determination of trace amounts of cadmium in food samples

A modified selective, highly sensitive and accurate procedure for the determination of trace amounts of cadmium which reacts with 1-(2-benzothiazolylazo)-2-hydroxy-3-naphthoic acid (BTAHNA) to give a deep violet complex with high molar absorptivity (7.05 × 10⁶ L mol⁻¹ cm⁻¹, 3.92 × 10⁷ L mol⁻¹ cm⁻¹, 1.78 × 10⁸ L mol⁻¹ cm⁻¹, and 4.10 × 10⁸ L mol⁻¹ cm⁻¹), fixed on a Dowex 1-X8 type anion-exchange resin for 10 mL, 100 mL, 500 mL, and 1000 mL, respectively. Calibration is linear over the range 0.2-3.5 μg L⁻¹ with RSD of ?1.14% (n = 10). The detection and quantification limits were calculated. Increasing the sample volume can enhance the sensitivity. The method has been successfully applied for the determination of Cd(II) in food samples, water samples and some salts samples without interfering effect of various cations and anions.     

Modeling calcium and water intake in threshed corn grain during thermo-alkaline treatment

A mathematical model describing simultaneous solvent diffusion and gelatinization of starch was used to explain the water and calcium absorption in threshed corn grains during the thermo-alkaline treatment. A computer-aided nonlinear optimization technique was used to find the effective diffusion coefficients and the reaction rate constants of water and calcium in threshed corn grains at boiling temperature (92.5 ± 0.3 °C). The mathematical model shows good correlation between measured and predicted values of water and calcium intake. It is concluded that the cooking process is limited by the reaction of starch components with water and calcium. The effective diffusion coefficient for water varied between 1.18 × 10⁻¹⁰ and 1.45 × 10⁻¹⁰ m²/s and for calcium between 8.55 × 10⁻¹⁰and 16.77 × 10⁻¹⁰ m²/s. The diffusion of water and calcium in threshed corn was produced with a reaction rate constants in the range of 6.83 × 10⁻⁴ to 10.4 × 10⁻⁴ s⁻¹ for water and 2.7 × 10⁻⁵–7.6 × 10⁻⁵ s⁻¹ for calcium. According to these effective diffusion coefficient values the diffusive process seems to be slower for water than for calcium. However, the reaction rate constant values are approximately 10 times higher for water than for calcium which may indicate that a higher amount of solvent was linked in the water diffusion process due to the gelatinization. Low concentration of Ca(OH)₂ such as 0.10% did not significantly affect the water diffusion of threshed corn during the cooking process.     

Superheated steam drying characteristic and moisture diffusivity of distillers’ wet grains and condensed distillers’ solubles

Samples of distillers’ spent grains were prepared by blending different proportions of distillers’ wet grains (DWG) with condensed distillers’ solubles (CDS). Such samples when dried with superheated steam (SS) at 110, 130 and 160 °C showed typical behaviour of drying in the falling rate period. The overall moisture diffusivity (D_m) increased with a decrease in moisture content under all drying conditions. An increase in moisture diffusivity with respect to the SS temperature was also observed. For all drying conditions, the values of average diffusivities (D_m)_avg non-corrected for shrinkage ranged from 0.52 × 10⁻⁹ to 3.08 × 10⁻⁹ m²/s. For distillers’ spent grains of different ratios of DWG to CDS, the decrease in SS temperature from 160 to 110 °C caused a decrease in (D_m)_avg by 69-82%. Increasing the amount of CDS added to the DWG from 0% to 100% caused an increase in (D_m)_avg by 14-35% for the temperature range tested in this study. The values of (D_m)_avg corrected for shrinkage ranged from 0.17 × 10⁻⁹ to 0.86 × 10⁻⁹ m²/s for all drying conditions studied. The decrease in SS temperature from 160 to 110 °C caused a decrease in (D_m)_avg by 70-74%. Not much differences were observed for the same drying temperatures and different ratios of DWG to CDS. The differences between the values of average overall moisture diffusivity (D_m)_avg corrected and non-corrected for shrinkage were significant, nearly one order of magnitude.     

Modeling water loss and oil uptake during vacuum frying of pre-treated potato slices

The objective of this research was to determine the kinetics of water loss and oil uptake during frying of pre-treated potato slices under vacuum and atmospheric pressure. Potato slices (diameter: 30 mm; width: 3 mm) were pre-treated in the following ways: (i) raw potato slices “control”; (ii) control slices were blanched in hot water at 85 °C for 3.5 min; (iii) blanched slices were dried in hot air until reaching a moisture content of ∼0.6 g water/g dry basis. The slices were fried under vacuum (5.37 kPa, absolute pressure, at 120, 130 and 140 °C) and atmospheric conditions (at 180 °C). Two models based on the Fick's law were used to describe water loss: (i) with a constant effective diffusive coefficient; and (ii) with a variable effective diffusive coefficient. Oil uptake data were fitted to an empirical model, with a linear behavior for short times whereas the model was time independent for long times. The variable diffusivity model better fitted experimental water loss, giving values of effective diffusivity between 4.73 × 10⁻⁹ and 1.80 × 10⁻⁸ m²/s. The proposed model for the study of the kinetics of oil uptake fitted the experimental data properly. Control and blanched vacuum fried potato chips increased their final oil contents to 57.1% and 75.4% respectively, when compared with those fried at atmospheric pressure. However, the oil absorption of dried vacuum fried potato chips diminished by ∼30%.