Diffusivity Deff Research Articles

Microwave-vacuum drying behavior of rosehips: Experimental investigation and mathematical modeling

In this study, the microwave-vacuum drying of rosehips (Rosa canina) was investigated and the effect of different drying conditions during the microwave vacuum drying process on the drying kinetics of rosehips was determined. For this purpose, microwave vacuum drying experiments were carried out until a moisture content less than 10 % by weight was attained at three power (50, 100, and 150 W) and three pressure (40, 75, and 110 mBar (abs)) levels. The drying times ranged from 75 to 195 min depending on the power level and vacuum degree applied. Seven different mathematical models, which are most commonly used in the literature, were fitted to the experimental data, and among these models, the most suitable model was selected by considering the statistical criteria of the highest regression coefficient (R2), the lowest chi-square (χ2), total squared error (SSE) and root mean square error (RMSE). The drying rate (DR) increased with increasing microwave power levels under all pressure levels. The Midilli model was proposed as the best-fit model for predicting the drying behavior of rosehip plants under all drying process conditions. The effective moisture diffusion (Deff) of rosehips under different drying conditions during the MVD process ranged from 5.81⨮10−8-17.32⨮10−8 m2/s and increased with the increasing microwave power at constant pressure.

Process Modeling and Convective Drying Optimization of Raspberry Pomace as a Fiber-Rich Functional Ingredient: Effect on Techno-Functional and Bioactive Properties.

This study aimed to transform raspberry pomace, a by-product of the berry industry, into a sustainable, fiber-rich functional ingredient using convective drying. Drying experiments were conducted at temperatures of 50, 60, 70, 80, and 90 °C to identify the optimal conditions that balance process efficiency and preservation of functional and bioactive properties. The best results were achieved at 70 °C, where a high drying rate (DR) of 0.46 kg H2O·kg-1 db·min-1, effective moisture diffusivity (Deff) of 1.53 × 10-10 m2·s-1, and activation energy (Ea) of 34.90 kJ·mol-1 were observed. The Page model accurately represented the drying behavior (R2 = 0.9965-0.9997). Total dietary fiber (TDF) content remained stable across temperatures (52.52-64.76 g·100 g-1 db), while soluble dietary fiber (SDF) increased by 43.40%, resulting in a solubility (SOL) of 71.8%, water-holding capacity (WHC) of 8.2 mL·g-1 db, and oil-holding capacity (OHC) of 3.0 mL·g-1 db. High retention of bioactive compounds was achieved at 70 °C, including phenolics (32.10 mg GAE·g-1 db) and anthocyanins (25.84 mg C3G·g-1 db), resulting in significant antioxidant activities (DPPH: 33.29 mg AAE·g-1 db, IC50 0.016 mg·mL-1; ABTS: 35.85 mg AAE·g-1 db, IC50 0.029 mg·mL-1). These findings demonstrated the potential of convective drying at 70 °C to efficiently transform raspberry pomace into a high-quality functional ingredient. This process promotes sustainable production and waste reduction in the berry industry.

The effect of cold plasma pretreatment on drying efficiency of beetroot by intermittent microwave-hot air (IMHA) hybrid dryer method: Assessing drying kinetic, physical properties, and microstructure of the product

This study examined the effects of cold plasma (CP) pretreatment with durations of 1, 3, and 5 minutes on drying kinetics, microstructure, and physical properties, including shrinkage, rehydration ratio (RR), and bulk density of beetroot dried samples using intermittent microwave-hot air (IMHA) drying at 40 °C and pulse ratios (PR) of 1 and 2. While increasing PR decreased drying rate (DR) and effective moisture diffusivity (Deff), increasing microwave power from 180 to 600 W increased both, reducing drying time and specific energy consumption (SEC). Extended CP-pretreatment doubled DR, 66% increased Deff, and 24% reduced SEC. Both increasing CP-pretreatment time and microwave power had similar effects on shrinkage, RR, and bulk density, but CP-pretreatment was more prominent; reducing shrinkage by 18%, bulk density by 23%, and increasing RR by approximately 36% in 5-minutes. X-ray imaging showed that 600 W of microwave power increased porosity by 87%, while 5-minute CP-pretreatment increased it by 27%. As the optimum condition, CP-pretreatment for 5 minutes, continuous microwave application, and 600 W of MW power produced the best kinetics and physical properties. Overall, the results demonstrated that the appropriate CP-pretreatment duration could produce high-quality dried samples.

Artificial intelligence as a tool for predicting the quality attributes of garlic (Allium sativum L.) slices during continuous infrared-assisted hot air drying.

Effective drying methods are a highly suitable solution for ensuring stable food supply chains, reducing postharvest agricultural losses, and preventing the spoilage of perishable fruits and vegetables. Moreover, machine learning techniques are innovative and dependable, especially in addressing food spoilage and optimizing drying processes. This study utilized a continuous infrared (IR) hot air dryer to dry garlic (Allium sativum L.) slices. The experiments were conducted at different levels of IR power, air velocities (V), and temperature (T). The relationships between the input process parameters (IR, T, and V) and response parameters, including effective moisture diffusivity (Deff), drying time, and physicochemical properties of the dried slices (rehydration ratio [RR], total color change, flavor strength, and allicin content in the garlic), were modeled using an artificial neural network (ANN). Our findings showed that the maximum Deff of 6.8×10-10m2/s and minimum drying time of 225min were achieved with an IR of 3000W/m2, an air velocity of 0.7m/s, and a temperature of 60°C. The total color change and RR values increased with IR and higher air temperature but declined with higher air velocity. Furthermore, the garlic's flavor strength and allicin content levels decreased as the IR and air temperature increased. The results demonstrated a significant influence of the independent parameters on the response parameters (p<0.01). Interestingly, the ANN predictions closely matched the test data sets, providing valuable insights for understanding and controlling the factors affecting drying behaviors.

Analysis of the interaction between airflow and high-voltage electric fields on drying characteristics of carrots using heat pump-electrohydrodynamics combined drying

The study investigates the drying characteristics of carrots under different coupling forms of airflow and high-voltage electric fields (parallel flow, PF, and cross flow, CF) using heat pump-electrohydrodynamics (EHD) combined drying. The results show that, compared to single heat pump drying, the combined drying under PF mode reduces carrot drying time by 13.33 %–31.58 %, increases effective moisture diffusivity (Deff) by 17.80 %–32.32 %, increases specific moisture extraction rate (SMER) by 12.25 %–34.26 %. While the combined drying under CF mode reduces carrot drying time by 12.5 %–18.18 %, increases Deff by 7.27 %–13.14 %, increases SMER by 4.64 %–12.58 %. The improvements in parameters under the CF mode are weaker than those under the PF mode. Additionally, the β-carotene content under PF mode is consistently higher than under CF mode. Based on the experimental results, the Modified Page model was improved, yielding an updated model MR = aexp(-(kt)^n), with an R2 value of up to 0.9999–1, which provides theoretical guidance for optimizing the heat pump-EHD combined drying process.

Drying kinetics and mathematical modeling of coconut meat slices: Insight into pretreatment and drying synergic effect

Coconut consumption provides nutritional and health benefits to humans. Yet, poor postharvest and preservation methods result in the loss of coconut fruit bunches yearly. Investigations into achieving drying techniques that result in optimum drying rates coupled with consumer's desired end products that are both commercially and nutritionally viable remain paramount in the food industry. Consequently, osmotic dehydration is commendable for its low-cost pretreatment merit. Therefore, the study examined the drying-kinetics, energy consumption, effective moisture diffusivity (Deff), vitamin C retention, color, and rehydration behavior of coconut cultivars (Sri Lanka Green Dwarf × Vanuatu Tall (SGD × VTT), Catigan (CAT), and Tacunan Green Dwarf (TGD)) meat slices. Samples were osmotically pretreated with sucrose solution (30 %/30 min) and subjected to oven drying (80, 90, 100, and 110 °C (air velocity of 2 m/s) and lyophilization (−45 ± 2 °C) methods. A mathematical model was employed to predict the effect of osmotic pretreatment on drying dynamics and the assessment of utilized energy, vitamin C content, color, and rehydration of coconut meat slices at different drying conditions. The oven-dried sample's color changed (p < 0.05) compared to lyophilized samples. Drying-kinetics models were validated using determination coefficient (R2) and root mean square error (RMSE). The Asymptotic model satisfactorily suited the samples' drying data goodness fitting based on R2≥0.90−0.99 and low RMSE ≤0.01−0.12 compared to other models for both drying methods. Deff ranged between 1.10 × 10−07 m2s−1 and 7.90 × 10−08 m2s−1 for all the drying methods. CAT sample retained high vitamin C content compared to SGD × VTT and TGD samples. Rehydration ratio values were significant at lower temperatures among oven-dried experimental samples whereas TGD samples exhibited a significant rehydration values compared to SGD × VTT and CAT lyophilized samples. Among the drying methods, oven drying exhibited low energy consumption with shorter drying time and optimum Deff per adopted temperature ranges compared to lyophilization. The study revealed that temperature, time, the sucrose solution, and the thickness of the coconut slices strongly influenced the drying kinetics of the osmotically pre-treated coconut meat slice's drying features.

Thin layer drying and effect of temperature on the drying characteristics of bushbuck (Gongronema latifolium) leaves

Determination of the drying properties of agricultural products holds several benefits, such as nutrient preservation, processing and storage. The effect of air temperature on the drying properties and kinetics of bushbuck leaves at 30, 40, 50, 60 and 70 °C temperature was investigated. The drying time declined as the temperature rose, indicating a falling rate drying phenomenon. Drying models such as Henderson and Pabis, Newton, Modified Page, Page, Midilli and others, Logarithmic, and Two-term were applied and fitted to the experimental data's moisture ratio. The non-linear regression fitting method results showed that the Midilli and other models gave the best-fit description for the drying process. The values obtained for the coefficient of determination (R2) were observed to have varied from 0.9948 to 0.9995 for the various drying models evaluated. In contrast, the sum of square error (SSE) and root mean square (RMSE) estimate was observed to vary from 0.0056 to 0.0007 and 0.0310 to 0.0163, respectively. On the estimate for the effective moisture diffusivity (Deff), it was observed that it depends on temperature and extends from 1.33×10−9 to 4.83×10−9 m2/s. The value of the activation energy was 26.05 kJ/mol. From this study, it can be deduced that the Arrhenius model could predict the temperature effect on the drying process of bushbuck leaves.

Ultrasound-assisted vacuum drying of limequat peels and characterization of thermal, morphological and functional properties

This work aimed to determine drying behavior and energy consumption of limequat peels dried using ultrasound-assisted vacuum drying (UAVD), vacuum-assisted drying (VAD), oven drying (OD) and vacuum drying (VD), and investigate thermogravimetric decomposition, morphological, elemental and spectral analyses of dried peels with energy efficiency analysis including specific moisture extraction rate (SMER), moisture extraction rate (MER) and specific energy consumption (SEC). The UAVD considerably shortened drying time by 49 %, 34 % and 15 % as compared to the OD, VAD and VD. The highest drying rate was achieved at the UAVD. The effective moisture diffusivity(Deff) values in descending order were UAVD>VD>VAD>OD. Proximate analysis showed that limequat peels dried using the UAVD had the highest fixed carbon (25.35 %) and ash (3.03 %) contents, but the lowest volatile matter (61.68 %). Dried limequat peels exhibited similar thermal decomposition behavior. The UAVD caused porous and rough surface formation, and microchanneling effect. Carbon (>62.56 %) and oxygen (>15.98 %) were the major elements in dried limequat peels. The lowest O/C (0.25) and H/C (0.85) ratios were obtained for the limequat peels dried using the UAVD. Fourier-transform infrared spectroscopy (FTIR) spectra showed primarily O–H, C–H, CO, CC and C–O–C stretching vibrations. The highest SMER (0.0053 kg/kWh) and MER (0.0012 kg/h) values, and the lowest SEC (188.27 kWh/kg) value were determined for the UAVD. In conclusion, the UAVD was found to be the most appropriate drying method for the drying of limequat peels.

Effect of ultrasonic pretreatment on textural properties and sensory attributes of cooked faba beans

Drying process extends the shelf-life of fresh faba beans and makes them available all year round. Dried and cooked faba beans are used to make a variety of traditional food products. Ultrasonic pretreatment, as a modern food processing technology, can shorten the drying time of fresh legumes and improve the quality and sensory properties of products. So, the present study aimed to analyze the impact of the ultrasonic treatment process (0, 5, 10, and 15 min, 40 kHz, and 150 W) on the mass transfer rate, drying time, and effective moisture diffusivity (Deff) of fresh faba beans. Also, the effect of ultrasonic treatment on textural properties and sensory attributes of cooked faba beans was studied. By using the ultrasonic process, the rate of water extraction from fresh faba beans, and thus their dehydration rate, can be increased. With increasing the duration of ultrasonic pretreatment from 0 to 15 min, the drying time of fresh faba beans decreased from 250 min to 150 min (p < 0.05). The Deff was calculated by Fick’s second law, and it significantly increased from 0.70 × 10−9 m2 s−1 to 1.05 × 10−9 m2 s−1 when the sonication duration was extended from 0 to 15 min (p < 0.05). The Page model best fitted the drying kinetic of fresh faba beans with a coefficient of determination (r) > 0.9968, and the sum of squared error (SSE) and root mean squared error (RMSE) were also closer to zero compared to other models. The rehydration ratio of dried faba beans (after cooking) significantly increased from 308.4 % to 327.1 % with the extension of processing time from 0 to 15 min (p < 0.05). The maximum and minimum crust hardness and texture firmness values were for the untreated and sonicated samples for 15 min, respectively. The sonication increased the sensory acceptance of the cooked faba beans and the highest appearance, odor, texture, flavor, and overall acceptance were for the 10 min sonicated faba beans.

Kinetics of Vegetable Oils (Rice Bran, Sunflower Seed, and Soybean) Extracted by Pressurized Liquid Extraction in Intermittent Process

The research focuses on optimizing vegetable oil production processes for human consumption, emphasizing green and efficient extraction methods using renewable solvents with minimal toxic residues. Pressurized liquid extraction (PLE), especially with ethanol, is studied for its efficiency and low solvent usage in intermittent processes. By evaluating extraction parameters and kinetics, the study aims to determine optimal conditions for higher extraction rates and yields, providing insights into production costs and other factors. Specifically, the research examines the behavior of extraction kinetics for vegetable oils like rice bran, sunflower seeds, and rolled soybeans. It also seeks to determine mass diffusivity in semi-continuous processes and to model PLE in intermittent processes using Fick’s Law and Mathematica Wolfram Software v11.2. The effective diffusivity (Deff) for rice bran oil in pressurized ethanol varied between 13.09 and 15.70 × 10−12 m2/s, and the Deff value of sunflower seed oil was between 8.10 and 12.60 × 10−12 m2/s. For rolled soybean oil, the Deff value ranged from 17.25 to 31.29 × 10−12 m2/s. The mass diffusivity values of vegetable oils in pressurized ethanol remained within the same order of magnitude. The mass diffusivity for PLE in an intermittent process presented values of 5.97 × 10−12 m2/s for rice bran oil with 3 extraction cycles. The Deff value for sunflower seed oil in pressurized ethanol was 1.38 × 10−12 m2/s, with 4 cycles, and for rolled soybeans, the Deff value was 1.77 × 10−12 m2/s in 3 cycles. The Deff value found in the intermittent extraction process was lower than that in the semi-continuous process. The total solvent renewal in the semi-continuous extraction process significantly impacted the diffusivity values for all extracted oils, as this process utilizes much more solvent compared to the intermittent process for all matrices studied. Various factors, including geometry, average particle diameter, extraction temperature, and rinse solvent volume, can affect the differences in curve behavior between the semi-continuous and intermittent processes. Despite these factors, the intermittent process is considered more viable for implementation due to its favorable economic and environmental characteristics, primarily because it requires a much smaller amount of solvent.

PEA GRAINS IN DRYING: UNRAVELING THE KINETICS OF HOT-AIR DRYING AND EXPLORING MATHEMATICAL MODELS FOR MOISTURE DIFFUSION

Pea drying studies were assessed to learn more about the kinetics and properties of drying in a hot-air dryer. Research was done on impact of temperatures and pre-treatments on drying behaviours. The drying rate graphs demonstrated that the entire drying procedure took place when rates were declining. To properly understand the experimental data, four mathematical models (Henderson &amp; Pabis, Page, Wang &amp; Singh, and Aghbashlo et al.) were used. The Page model was discovered to be the ideal one to depict peas' curves of drying. The identification of the Page model as the most suitable for depicting pea drying curves underscored the applicability in modeling drying behaviors in similar agricultural products. With Fick's second law of diffusion, effective moisture diffusivity (Deff) sorted from 2.45x10-10 to 6.55x10-10 m2/s at given temperature. Deff was expressed as a function of temperature with an Arrhenius type equation. For samples from Potas, Blanch, and Control codes, the activation energy for moisture diffusion was computed as 21.48, 22.82, and 22.32 kJ/mol, respectively. The computation of activation energy for moisture diffusion for different samples offered practical information for optimizing drying processes under various conditions. The results showed the importance of pea drying kinetics and practical implications for industry on drying efficiency and product quality.

Drying kinetics of lemon (Citrus lemon) seeds on forced-air convective processing

The convective drying kinetics of Citrus lemon seeds at different air temperatures (60–160 °C, 0.3 m.s−1), as well as the effect of air velocity (v) and technology (tray and rotary drum (RD) drying), were investigated. Internal seed temperature profiles showed that most of the process would occur under internal mass transfer control. Each drying curve was fitted with a theoretical diffusion model to determine the effective diffusivity (Deff), and with nine empirical models. Deff were 0.65 × 10−10-13.10 × 10−10 m2.s−1 and the activation energy was 19.90 kJ.mol−1. Deff increased by 85% when v was raised by 50%; this effect was partially compensated by seed movement when using RD (62% increment). A two-term exponential model with arrangements over the pre-exponential terms demonstrated the complementarity of both terms in explaining the seed dehydration process. In addition, convective heat transfer coefficients were calculated (0.48–0.65 W.m−2 K−1). Overall, the results provide valuable kinetic parameters to characterize the dehydration process for further design and simulation of drying equipment.

Microwave-vacuum drying: Modeling validation of drying and rehydration kinetics, moisture diffusivity and physicochemical properties of dried dragon fruit slices

This study investigated the drying of dragon fruit slices with varying samples (0.5 cm, 1 cm, and 1.5 cm) using a microwave-vacuum dryer at power levels of 400 W, 600 W, and 800 W, under a vacuum pressure of 600 mm Hg. The comprehensive assessment included drying kinetics, effective moisture diffusivity (Deff), rehydration behavior, color changes, and ascorbic acid content. Results indicated a substantial moisture content reduction from an initial 614.28% to an average of 7.14% (dry basis) post-microwave vacuum drying. The Wang and Singh model proved most suitable, exhibiting high R2 values and low RMSE values, providing accurate insights into the drying process. Dragon fruit samples showed Deff values from 4.381 × 10−3 to 4.084 × 10−2 cm2/min, increasing with microwave power level. Rehydration, modeled by the Peleg model, revealed that the highest power level had the highest R2 and lowest RMSE values. Notably, 1.5 cm slices at 400 W exhibited minimal color change (18.32) and retained the most ascorbic acid (6.94 mg/100 g). This study offers valuable insights into dragon fruit drying, highlighting its impact on moisture content, modeling, and product quality.

Experimental investigation, performance analysis, and optimization of hot air convective drying of date fruits via response surface methodology

A laboratory-scale hot air convective dryer (HACD) was used to dry date fruits surplus at 0.5 ± 0.02 kg kg−1 to a safe moisture level of 0.35 kg kg−1 under drying temperatures (T) of 50–70 °C with airflow rates (Q) of 0.18 and 0.28 m3 h−1. Kinetics, modeling, energy, economic feasibility, and color difference of the date fruits were analyzed and then optimized using response surface methodology (RSM) with two drying factors and eight responses. The drying time to reach the desired moisture level ranged from 9 to 28 h under different drying conditions. The proposed mathematical model expressed the moisture behavior over drying time with the highest R2 = 0.9998 and 0.9999, respectively, for 0.18 and 0.28 m3 h−1. Effective moisture diffusivity (Deff) was calculated using the starting accessibility parameter and varied between 9.9 × 10−8 and 3.3 × 10−7 m2 s−1. The energy analysis revealed that the specific energy consumption (SEC) varies between 22.04 and 43.05 kWh.kg−1 and the drying efficiency (η) are 16.91, 16.14, and 25.38% for 50, 60, and 70 °C, respectively. The RSM optimization using a multi-level design with two centurium points denoted the optimum responses for the highest drying temperature. The lowest payback period (Pb) of the drying system was estimated to be 0.45 years for T = 70 °C and Q = 0.28 m3 h−1. The optimum drying time, Deff, total energy consumption (Et), SEC, η, and total color change (ΔE) were estimated to be 9 h, 3.3 × 10−7 m2 s−1, 33.91 kWh, 22.04 kWh.kg−1, 27.69%, and 1.69, respectively.

On the modelling of the effective longitudinal diffusion in bi-continuous chromatographic beds

We report on the possibility to extend to bi-continuous packings the two models for the effective longitudinal diffusion Deff, or B-term band broadening, recently proposed for discontinuous chromatographic beds. In bi-continuous packings, like monolithic columns, solutes experience a connected end-to-end pathway in both the mobile and stationary zones, as opposed to discontinuous packings, wherein the stationary adsorptive zone is distributed over a set of isolated elements. Since it is unclear whether a densely packed bed of spherical particles should be treated as a continuous or a bi-continuous medium, this extension is also crucial to fully understand the behaviour of packed particle beds. The proposed models for the effective longitudinal diffusion Deff originate from the adoption of the Two Zone Moment Analysis (TZMA) method by which Deff can be expressed as a linear combination of two essential quantities γm and γs, referred to as effective zone-diffusion factors. In the present work we propose two analytical models for γm and γs that now cover both the discontinuous and the bi-continuous case. To validate the theory, several bi-continuous packings are investigated, including the tetrahedral skeleton model (TSM), six different Triple Periodic Minimal Surface (TPMS) monoliths and randomly packed beds of spheres. For all of these, the models provide highly accurate results for Deff over a wide range of porosities and zone retention factors k″. The comparison with literature experimental data for both monolithic silica columns and columns packed with fully porous and porous-shell particles is also presented.

Convective Drying of the Zucchini Slices; Impact of Pretreatments on the Drying Characteristics and Color Properties, Evaluation of Artificial Neural Network Modeling and Thin-Layer Modeling

This study focused on the impact of citric acid, hot water blanching, and ultrasound pretreatment on the drying of zucchini slices, color properties, and the comparison of artificial neural network (ANN) and thin-layer modeling. The pretreatments enhanced the drying rate and reduced drying time. Ultrasound pretreatment was observed as the most effective, with a reduction rate of the drying time as 40%. Besides, mass transfer and moisture diffusion phenomena were positively affected by pretreatments, depending on the increment of the drying rate. The highest mass transfer coefficient (hm), moisture diffusivity (D) by the Dincer and Dost model, and effective moisture diffusivity (Deff) by the Crank equation were obtained with ultrasound pretreatment. On the other hand, Midilli and Kucuk, Parabolic, and Page gave the best predictions among the thin-layer models. However, ANN modeling had a better performance than thin-layer modeling due to a higher determination coefficient (R2) and lower root mean square error (RMSE) values. Color properties of the zucchini slices were affected by drying processes. In general, the redness and yellowness of the zucchini slices increased; however, lightness did not show statistical significance. Additionally, citric acid pretreatment gave the lowest total color difference (∆E).

Changes in Moisture Desorption Rate of Shelled Corn Layers in a Low-Temperature Deep-Bed Drying Column

To optimize grain drying processes, high-moisture shelled corn was dried in a device using a combination of three temperatures (45, 55 and 65 °C) and hot-air velocities (0.7, 1.1 and 1.3 m·s-1). The grain moisture and temperature, and the relative humidity (RH) of interstitial airflow were determined intelligently in grain layers of 7.5 to 32.5 cm with 5.0 cm intervals. The change in RH of interstitial airflow in grain layers of 7.5-27.5 cm with drying time all revealed the shape of a hyperbolic line and took turns to lag. These RH lines shortened with an increased drying temperature from 45 to 65 °C and hot-air velocity from 0.7 to 1.3 m·s-1. The temperature lines were raised and shortened with an increase in drying temperature and hot-air velocity. A modified moisture diffusion exponential equation was developed to analyze the moisture desorption rate of corn kernels. For the average sorption rate curve from grain layers of 2.5-32.5 cm at 1.3 m·s-1 of hot air, the transition points from adsorption to desorption occurred at 2.4 h, 2.7 h, and 3.0 h with drying temperatures of 65 and 45 °C, respectively, and represented the earliest and largest initial desorption rates among the three hot-air velocities. The moisture desorption rate of samples increased with increasing drying temperature. Compared with the average value of grain layers, at the same hot-air velocity, the kernel effective diffusivity (Deff) values dried at 55 °C were correspondingly higher than those dried at 45 and 65 °C. At the same drying temperature, the kernel Deff values tended to increase with an increase in hot-air velocity, whereas the activation energy decreased. These results suggested that an increase in drying temperature and hot-air velocity may considerably shorten adsorption time and increase desorption rates of shelled corn in deep bed drying.

Comparative study on microwave and tray drying of beef: Effect of partial salt replacement on drying kinetics and structural characteristics

Beef cuts were dried by tray drying (TD), microwave drying (MD), and TD+MD. Salting as pre-treatment was carried out with NaCl or NaCl+KCl salts to evaluate the effect of sodium reduction. The beef was divided into nine groups: three were subjected to TD, MD, and TD+MD; for the other six groups, dry salting was applied with 100% NaCl or 50% NaCl + 50% KCl, followed by MD, TD, or TD+MD. Processing times of TD, MD, and TD+MD were about 660, 250, and 300 min, and effective diffusivities (Deff) were 1.33 × 10-8, 3.88 × 10-8, and 3.57 × 10-8 m2/s, respectively. Compared with TD, the MD procedure resulted in significantly harder texture and lower rehydration ratio (p &lt; 0.05). SEM images of dried beef indicated fractures and disruption after TD, while a compact structure was obtained with MD. Both salt types contributed a softer texture in rehydrated MD, but KCl did not change the hardness values of dried meat. MD could have great potential for drying meat by reducing drying time, and KCl could be applied as a substitute for NaCl without adversely affecting the structural quality.

DRYING OF CHERRY LAUREL JUICE USING FOAM MAT DRYING TECHNIQUE AND INVESTIGATING THE EFFECT OF DRYING TEMPERATURE ON DRYING CHARACTERISTICS AND BIOACTIVE COMPONENTS

This study aimed to optimize the foam properties for the foam mat drying (FMD) process and investigate the effect of drying temperatures (60, 70, and 80 °C) on the cherry laurel juice's drying characteristics and bioactive properties. Egg white protein (EWP), carboxymethyl cellulose (CMC), and mixing time (MT) variables were optimized using the Taguchi method to achieve the juice foam with maximum foam capacity and stability. The optimal conditions determined were 10% EWP, 0.3% CMC, and 12 min of MT. The drying times and effective moisture diffusivities (Deff) for 60, 70, and 80 °C were recorded as 160, 120 and 90 min and 6.09×10-9, 7.74×10-9 and 11.33×10-9 m2/s, respectively. As the drying temperature increased, the total phenolic and total monomeric anthocyanin contents, and antioxidant activity values increased, but ascorbic acid content decreased. This research demonstrates that the FMD process can successfully be applied to dry juices with pronounced bioactive properties.

Evolution and Modelling of the Moisture Diffusion in Walnuts during the Combination of Hot Air and Microwave–Vacuum Drying

To understand the moisture transfer mechanism of walnuts during the combination of hot air (HA) and microwave–vacuum (MV) drying (HA-MVD) process, the drying characteristics and moisture diffusion characteristics of walnut during HA-MVD were investigated. The results indicated that the HA-MVD of walnuts occurred mainly in the falling-rate stage. The value of effective moisture diffusivity (Deff) dropped continuously with the decrease in moisture content (MC) during the HA drying, while switching to MV drying could truncate the decrease in Deff and still maintain a high value until the end of drying. The HA temperature, MC of the transition point, microwave power, and MV thermostatic temperature have significant effects on the moisture diffusion characteristics of walnuts. The values of Deff for walnuts ranged from 2.33 × 10−9 m2/s to 6.89 × 10−8 m2/s. The third-order polynomial prediction model of Deff related to the sample MC and drying conditions was established to describe the dynamic change in the Deff of walnuts during the HA-MVD process. The application of MVD in the final stage of drying could rapidly increase the internal vapor pressure of the walnuts, accelerate the diffusion speed of the internal moisture, and re-enhance the drying rate. The findings have practical value for the development of efficient and energy-saving drying methods in the walnut industry.