Effective Water Diffusivity Research Articles

Understanding of Water Transport through Membrane Electrode Assembly in PEFC

In a polymer electrolyte fuel cell (PEFC), water generation, electroosmosis drag, and back diffusion change the humidity, which affects transport properties such as proton conductivity, effective oxygen diffusion coefficient, and permeance of the feed gas through a membrane. Since the sorption and desorption of water in the electrolyte membrane is slower than other processes such as the oxygen reduction reaction, the proton transport, and the oxygen diffusion, dynamic water behavior should be considered to estimate the cell performance precisely. In this study, the water permeation flux through a membrane electrode assembly (MEA) was measured, and the effective water diffusion coefficients in a membrane and catalyst layer (CL) were formulated as a function of temperature and the moisture content respectively. Dynamic moisture content change in MEA was simulated with the measured effective diffusion coefficients. The experimental results showed that desorption was slower than sorption in the identical moisture content range particularly at the beginning, and this tendency was successfully reproduced using the moisture content distribution obtained by numerical simulation.

Thermo-economic analysis of sun drying patio coffee in the Sierra Mariscal, Chiapas-México

This study shows a thermo-economic analysis of patio coffee drying in the Sierra Mariscal Chiapas-México to optimize bed thickness. The drying time, specific energy, thermal efficiency, water-effective diffusivity, and drying batch costs were correlated with bed thickness and solar irradiation. The initial and final coffee moisture contents were 53 % and 11–12 % (w.b). The bed thickness was in terms of kilograms of coffee uniformly spread on a square meter (2.0, 5.0, 10.0, 15.0, and 20.0 kg/m2). The five experimental campaigns involved five tests over a harvest season. The water-effective diffusion coefficient increases with bed thickness (0.38–91.2 × 10−10 m2/s). The solar irradiation requirement and the efficiency of the patio drying linearly increase with bed thickness while specific energy exponentially decreases. The lower specific energy was (7.1–10.4 MJ/kg) for the higher bed thickness (20.0 kg/m2), with (24.0–38.0 h) of drying time and (0.22–0.32) of efficiency. The optimized coffee bed thickness was 10 kg/m2, with a specific energy of 8.8–9.6 MJ/kg. When bed thickness increases, the thermal efficiency increases almost linearly 5.5 times, exponentially reducing the drying cost per batch five times. However, increasing drying times shall lessen the quality of physical-chemical and sensorial coffee.

Quality and Process Optimization of Infrared Combined Hot Air Drying of Yam Slices Based on BP Neural Network and Gray Wolf Algorithm

In this paper, the effects on drying time (Y1), the color difference (Y2), unit energy consumption (Y3), polysaccharide content (Y4), rehydration ratio (Y5), and allantoin content (Y6) of yam slices were investigated under different drying temperatures (50–70 °C), slice thicknesses (2–10 mm), and radiation distances (80–160 mm). The optimal drying conditions were determined by applying the BP neural network wolf algorithm (GWO) model based on response surface methodology (RMS). All the above indices were significantly affected by drying conditions (p < 0.05). The drying rate and effective water diffusion coefficient of yam slices accelerated with increasing temperature and decreasing slice thickness and radiation distance. The selection of lower temperature and slice thickness helped reduce the energy consumption and color difference. The polysaccharide content increased and then decreased with drying temperature, slice thickness, and radiation distance, and it was highest at 60 °C, 6 mm, and 120 mm. At 60 °C, lower slice thickness and radiation distance favored the retention of allantoin content. Under the given constraints (minimization of drying time, unit energy consumption, color difference, and maximization of rehydration ratio, polysaccharide content, and allantoin content), BP-GWO was found to have higher coefficients of determination (R2 = 0.9919 to 0.9983) and lower RMSEs (reduced by 61.34% to 80.03%) than RMS. Multi-objective optimization of BP-GWO was carried out to obtain the optimal drying conditions, as follows: temperature 63.57 °C, slice thickness 4.27 mm, radiation distance 91.39 mm, corresponding to the optimal indices, as follows: Y1 = 133.71 min, Y2 = 7.26, Y3 = 8.54 kJ·h·kg−1, Y4 = 20.73 mg/g, Y5 = 2.84 kg/kg, and Y6 = 3.69 μg/g. In the experimental verification of the prediction results, the relative error between the actual and predicted values was less than 5%, proving the model’s reliability for other materials in the drying technology process research to provide a reference.

Thin‐Layer Drying Model, Drying Rate, and Effective Water Diffusion Coefficient of Pelleted Feed

In this study, classic thin‐layer drying models such as the Page model, Verma model, and Two‐term model were used to fit the thin‐layer drying data of feed. Based on this, a novel thin‐layer drying model for pelleted feed (modified Verma model) was proposed. The results indicate that the new model is the optimal choice for describing the drying kinetics of pelleted feed for growing pig and calf. The drying rate of pelleted feed is linearly correlated with the feed moisture content. The effective water diffusion coefficient for pelleted feed of growing pig and calf ranges from 1.86 × 10−10 to 2.75 × 10−9 m2/s and 3.32 × 10−10 to 3.87 × 10−9 m2/s, respectively. The activation energy (Ea) for moisture diffusion in both types of feed is 26.42 kJ/mol and 25.86 kJ/mol, respectively. By establishing predictive models for model parameters based on air temperature and air velocity variables, the new model demonstrates extrapolation capability, wide applicability, and practical value. This work lays the foundation for developing a similarly characterized deep‐bed cooling drying model for pelleted feed.

Water Effective Diffusion Coefficient in Dairy Powder Calculated by Digital Image Processing and through Machine Learning Algorithms of CLSM Micrographs.

Rehydration of dairy powders is a complex and essential process. A relatively new quantitative mechanism for monitoring powders' rehydration process uses the effective diffusion coefficient. This research focused on modifying a previously used labor-intensive method that will be able to automatically measure the real-time water diffusion coefficient in dairy powders based on confocal microscopy techniques. Furthermore, morphological characteristics and local hydration of individual particles were identified using an imaging analysis procedure written in Matlab©-R2023b and image analysis through machine learning algorithms written in Python™-3.11. The first model includes segmentation into binary images and labeling particles during water diffusion. The second model includes the expansion of data set selection, neural network training and particle markup. For both models, the effective diffusion follows Fick's second law for spherical geometry. The effective diffusion coefficient on each particle was computed from the dye intensity during the rehydration process. The results showed that effective diffusion coefficients for water increased linearly with increasing powder particle size and are in agreement with previously used methods. In summary, the models provide two independent machine measurements of effective diffusion coefficient based on the same set of micrographs and may be useful in a wide variety of high-protein powders.

Evaluation of water diffusion, water vapor permeability coefficients, physicochemical and antimicrobial properties of thin films of nopal mucilage, orange essential oil, and orange pectin

There is a growing interest in the development of biodegradable, safe materials to extend the shelf life of food and replace non-biodegradable plastics. Several materials have been investigated that can be used as edible coatings to extend the shelf life of fruit and vegetable products. In the present work, the design and characterization of different films of nopal mucilage, orange pectin, and orange essential oil were investigated for their potential use as edible coatings. It was found that the pectin concentration had a significant effect (p<0.05) on the thickness, color, and transparency of the edible films. According to the results, the formulation 0.5% mucilage-0.25 % pectin-0.25 % essential orange oil was chosen. Infrared spectroscopy showed no changes in the chemical compounds of the film formulation. The XRD pattern showed that this thin film is amorphous and contains calcium oxalate of nopal mucilage and oleic acid. In the water vapor permeability tests, the films containing orange essential oil in their formulation showed a higher effective water diffusion and water permeability coefficients as compared to the other formulations. In addition, the concentration of orange essential oil has an antimicrobial effect (p<0.05) on some bacteria of interest for food safety. This work demonstrates a new methodology and measurement technique to determine the effective water diffusion and water permeability coefficients for edible thin films based on the photoacoustic effect.

Effect of Sonication and Edible Coating on Total Phenolic Content, Antioxidant Capacity, and Physical Characteristics of Infrared-Dried Sweet Cherries

This research studied the influence of combined ultrasonic (40 kHz, 150 W, for 3 min) and 0.2% xanthan gum (XG), guar gum (GG), and wild sage seed gum (WG) coating pretreatments on total phenolic content, antioxidant activity, drying time, effective water diffusivity coefficient ( D eff ), rehydration ratio (RR), total color difference ( Δ E ), and surface shrinkage (SS) of infrared-dried sweet cherries. The ultrasonic pretreatment increased the water transfer rate and water diffusivity during infrared drying and decreased the drying time of fresh sweet cherries. The edible coating enhanced the total phenolic content, antioxidant activity, dehydration time, and RR and decreased the D eff , Δ E , and SS values of infrared-dried sweet cherries. The highest value of total phenolic content (3469.7 μg galic acid/g dry) was recorded for pretreated sweet cherry samples by GG. The mean antioxidant activities for uncoated, XG-coated, GG-coated, and WG-coated sweet cherries were 35.64, 59.88, 54.38, and 61.19%, respectively. In this study, the sweet cherry D eff varied from 2.23 × 10 − 9 m2/s (for untreated cherries) to 5.00 × 10 − 9 m2/s (for sonicated and uncoated cherries). The experimental data for the drying curves were fitted to various single-layer equations, and the Page equation using the experimental constants best described the drying rate of sweet cherries. The mean Δ E values for uncoated, XG-coated, GG-coated, and WG-coated sweet cherries were 15.11, 9.91, 8.74, and 10.69, respectively.

Effects of ultrasound and microwave pretreatments of carrot slices before drying on the color indexes and drying rate

The aim of this study was to examine the impacts of microwave pretreatment (MWP) and ultrasonic pretreatment (USP) on drying time (DT), mass transfer kinetics, effective water diffusivity (Deff), rehydration rate, color index (L*, a*, b*), and the surface shrinkage of carrot slices when dried in a hot air dryer (70 °C). The microwave process was performed for 0, 15, 30, 45, and 60 s before drying of carrot slices. In addition, the ultrasound process was performed in an ultrasonic bath (40 kHz and 150 W) for 0, 5, 10, 15, and 20 min. The results confirmed that the MWP and USP decreased the DT (higher water loss) of carrot slices. Deff values for microwave-pretreated slices were considerably higher than those for nontreated carrot slices (p < 0.05). The Deff calculated by Fick's second law was increased from 8.69 × 10−10 to 10.96 × 10−10 m2 s−1, and from 7.56 × 10−10 to 9.39 × 10−10 m2 s−1, for samples pretreated by microwave and ultrasound, respectively. The empirical value for the drying curves were fitted to the common thin film-equations, and Page's equation was the most suitable to describe the dehydration rate of carrot slices. The average rehydration ratio of nontreated, microwave-treated, and ultrasound-treated carrot slices were 432.3 %, 449.2 %, and 360.9 %, respectively. The redness, yellowness, and surface shrinkage parameters of pretreated samples by microwave were higher than the nontreated slices. The lightness and redness parameters of pretreated carrot slices by ultrasound were higher than the nontreated samples under all conditions.

Effects of gum-based coatings combined with ultrasonic pretreatment before drying on quality of sour cherries

Application of pretreatment methods such as ultrasound and edible coatings is used to reduce processing time and/or preserve food product quality in drying technology. The aim of this research was to measure the impacts of gum-based coatings (guar, sodium alginate, and basil seed gums) in combination with sonication before drying on total phenolic content (TPC), antioxidant capacity (AC), effective water diffusivity (Deff), total color difference (ΔE), surface shrinkage (SS), and rehydration ratio (RR) of sour cherries. Ultrasonic pretreatment (40 kHz, 150 W, at 25 °C, for 12 min) increased the TPC, AC, Deff, and RR, and decreased the drying time, ΔE, and SS values of sour cherries. Edible coating increased the TPC, AC, drying time, and RR, and decreased the Deff, ΔE, and SS values of sonicated sour cherries. The TPC for untreated, uncoated-sonicated, guar gum-coated, sodium alginate-coated, and basil seed gum-coated sour cherries were 2965.9, 3398.1, 3480.8, 3511.0, and 3898.3 µg gallic acid equivalent/g dry, respectively. The highest value of AC (71.2±3.7 %) was observed on coated sour cherries by basil seed gum. The experimental data for drying curves were fitted to several widely used models, and the Midilli model using the experimental constants that best represent the drying rate of sour cherries. The edible coatings significantly reduced the color changes and shrinkage of dried sour cherries, with the lowest ΔE and SS values in the basil seed gum-coated samples (p < 0.05).

Evaluation of osmodehydration and vacuum-assisted osmodehydration as pre-treatments during fruit drying process: The effect on drying rates, effective water diffusion and changes in product quality

This work evaluates the effect of applying osmodehydration (OD40 at atmospheric pressure) and pulsed-vacuum osmodehydration (ODVP40, at 498 mmHg) as pre-treatments before apple (cv. Granny Smith) drying. The pre-treatments were evaluated in terms of time-dependent free moisture content (MK), drying rates (DR), effective water diffusion (D), product shrinkage and color changes. The ODVP40 pre-treated samples (40 °Brix grape juice at 40 °C) had a higher total soluble solids content (p < 0.05) and lower moisture content (p < 0.05). Drying experiments were performed at three temperatures (50, 60, and 70 °C) and 3.5 m/s air-flow. Page model best fitted the MK (R2 >0.996) and DR (R2 >0.827). A response surface model was used to estimate the Page model parameters as a function of the initial sample's temperature (T) and total soluble solids concentration (SSo). D values (considering product shrinkage) were computed as 3.56–5.48 × 10−10 m2/s, 6.86–14.35 × 10−10 m2/s, 30.70–72.81×10–10 m2/s for fresh, OD40 and ODVP40 apple, respectively.

Effect of ultrasonic power on moisture migration and microstructure of contact ultrasound enhanced far-infrared radiation drying on taro slices

To clarify the moisture migration and microstructure of taro in contact ultrasound enhanced far-infrared radiation drying (CUFRD), low-field nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), paraffin sectioning and microscopic observation techniques were applied to explore the changes of the drying curves, water status, microstructure, porosity, microscopic images and distribution curves of cell microstructure parameters of taro under different ultrasound powers of 0, 40, and 80 W. The results showed that applying contact ultrasound (CU) during drying was beneficial to accelerating the dehydration process and improving the porosity of taro slice. With the augment of CU power, the drying times of taro reduced by 16.67% to 25.00%, and the effective water diffusion coefficient was improved by 14.72% to 31.38%. In addition, the application of CU resulted in an increase firstly and then decrease in the cross-sectional area and perimeter distribution curves of taro cells and a widening of the peak shape of the distribution curve of taro cell roundness. In conclusion, CU application could cause faster internal moisture migration, and higher CU power had more obvious effect on microstructure and cell morphological parameters of taro during CUFRD.

Discrepancy of Effective Water Diffusivities Determined from Dynamic Vapor Sorption Measurements with Different Relative Humidity Step Sizes: Observations from Cereal Materials

Water diffusivity, a critical parameter for cereal processing design and quality optimization, is usually concentration-dependent. dynamic vapor sorption (DVS) system provides an approach to establishing the relationship between water concentration and diffusivity. However, the usual relative humidity (RH) jump during practical sorption processes is usually greater than that adopted in DVS measurements. Water vapor sorption kinetics of glutinous rice grains, glutinous rice flour and wheat flour dough films were measured using the DVS system to verify if varying RH step sizes can obtain identical diffusivities within the same range. The effective diffusivities were determined according to Fick's second law. The results revealed that increasing RH step size led to a higher estimated diffusivity, regardless of whether the water concentration gradient or potential chemical gradient was considered a driving force for water diffusion. This finding was further confirmed by a linear RH scanning DVS measurement. The water concentration-dependent diffusivity obtained from a multi-step DVS measurement, according to Fick's second law, will overestimate the required time for practical cereal drying or adsorption. Thus, this paradoxical discrepancy needs a new mass transfer mechanism to be explained.

Monitoring the Changes in Heat Transfer and Water Evaporation of French Fries during Frying to Analyze Its Oil Uptake and Quality.

The effect of frying temperature on heat transfer, water loss kinetic, oil uptake kinetic, and quality of French fries was evaluated. With increasing frying temperature, the core temperature of fries increased, and the Biot number and heat transfer coefficient (h) first decreased and then increased significantly (p < 0.05). The water loss rate (kw) and water effective diffusion of fries increased with the increasing frying temperature. The kw of fries fried at 150−190 °C were 0.2391, 0.2414, 0.3205, 0.3998, and 0.3931, respectively. The oil uptake rate (ko) first increased and then decreased with increasing frying temperature, and the ko of samples fried at 150−190 °C were 0.2691, 0.2564, 0.4764, 0.3387, and 0.2522, respectively. There were significant differences in the a*, L*, ΔE, and BI between fries with different temperatures (p < 0.05), while there was no significant difference in the b* (p > 0.05). The hardness and crispness of fries increased with increased frying temperature. The highest overall acceptability scores of fries were fried at 170 °C. Therefore, the changes in color, texture overall acceptability, and oil content were due to the Maillard reaction and the formation of porous structure, which was induced by h and water evaporation of fries when they changed.

Dynamic Water Transport through the Perfluorinated Sulfonic-Acid Membrane

IntroductionThe proton exchange membrane (PEM) is indispensable material for proton transport in PEFC. Since RH affects the effective proton conductivity and the effective oxygen diffusivity through the catalyst layer as well as the proton conductivity, the electroosmotic drag coefficient, the effective diffusivity of water, and the gas permeances of PEM, water behavior which determines relative humidity is most important.To estimate the PEFC performance over time, the dynamic change in transport properties of PEM should be reproduced over full range of operating temperature and moisture content. Though water diffusion in Nafion™ membrane was extensively investigated [1, 2], the transport properties have not been formulated as the function of both temperature and moisture content. In this study, the effective water diffusivity and the skin layer water transfer coefficient were formulated from the experimental results measured by the permeation method and the sorption/desorption method.Experimental–Permeation experimentsA Nafion™ membrane, NR-212, N115 or N117 with different thickness (at relative humidity, RH of 50 %), 51 μm, 127 μm, and 183 μm, respectively, was set in a Japan Automobile Research Institute (JARI) standard cell whose active area was reduced to 2.0 cm×2.0 cm. The cell was placed in the constant temperature and humidity oven (ESPEC, LHL-113). Nitrogen was supplied to both sides of the cell at 300 cm3/min (20 °C, 1 atm). The relative humidity of the supplied gas was controlled by the bubbler temperature. The water vapor flowing out of the cell was collected with an ice-cooled trap to estimate the water permeation flux of the membrane.–Sorption/desorption experimentsThe membrane was placed in a desiccator in which RH was controlled by saturated salt solution method at room temperature (22 °C). The weight of the membrane was recorded constantly. After reaching equilibrium, the membrane was placed in another RH condition and weighed.Results and discussionThe moisture content of the membrane, λ was calculated by a GAB sorption equation in which paraments were fit using reported water equilibrium experimental data [3, 4, 5, 6] as shown in Fig. 1. Schematic diagram of permeation mechanism is shown in Fig. 2. Water permeation flux through the membrane, N A (M) is expressed as follows: N A (M)=c (M) ρ (M) (λ -m -λm )/(1/k A++1/k A-+δ (M)/D eA (M)) (1)where c (M) is the ion-exchange capacity [mol/kg], ρ (M) is the density of dry membrane [kg/m3], λ is the moisture content, k A is the skin layer mass transfer coefficient [m/s], δ (M) is the membrane thickness [m] and D eA (M) is the effective diffusivity [m2/s]. The subscript A means absorbed water, m is the surface of the membrane, - is the supply side and + is the permeate side. Total resistances calculated by eq. (1) were plotted against the membrane thickness. D eA (M) and k A calculated from the trendlines are shown in Figs. 3 and 4, and Arrhenius plots of D eA (M) are shown in Fig. 5.Skin layer mass transfer coefficient, k A can be obtained directly from the sorption/desorption experiments at low temperature. k A obtained from the permeation and sorption/desorption experiments are summarized in Fig. 6 and they are located on an identical line. The transport properties at λ= 5 are expressed as follows as an example: D eA (M) = 3.35×10–5 m2 s–1 exp(–3760 K/T) k A = 1.27×105 ms–1 exp(–8330 K/T)Since these transport properties depend on the moisture content, the desorption is faster than sorption and vice versa even at completely same range of moisture content. This is because the moisture content in the skin layer is always different during sorption and desorption even with the same moisture content variation range.ConclusionsFrom the permeation experiments and the sorption/desorption experiments, the transport properties over wide range of temperature and moisture content of the perfluorinated sulfonic-acid membrane were formulated. Considering the change in k A and D eA depending on the moisture content, the sorption and desorption rate are unequal even in identical RH range.AcknowledgementThis work was supported by the FC Platform Program: Development of design-for-purpose numerical simulators for attaining long life and high-performance project (FY 2020–FY 2022) conducted by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Dynamic Water Transport through the Perfluorinated Sulfonic-Acid Membrane

Proton exchange membrane (PEM) is essential material for the proton transport in a polymer electrolyte fuel cell (PEFC). Since relative humidity (RH) in a cell affects the effective proton conductivity and the effective oxygen diffusivity through the catalyst layer as well as the proton conductivity, the electroosmotic drag coefficient, the effective diffusivity of water, and the gas permeances of the PEM, water behavior which determines relative humidity is important. To estimate the PEFC performance over time, the dynamic change in the moisture content of the PEM is needed to know. In this study, the PEM is considered to consist of a bulk layer and skin layers on both sides of the bulk layer. The bulk layer effective diffusion coefficient and the skin layer water transfer coefficient were formulated from the experimental results measured by the steady-state permeation method and the unsteady-state sorption and desorption method.

Development of a differential photoacoustic system for the determination of the effective water diffusion and water vapor permeability coefficients in thin films

This paper focused on developing a methodology and metrology using a differential photoacoustic (PA) system to determine the effective water vapor diffusion coefficient (Deff) and the effective permeability coefficient (Π) in thin films as a piece of paper and standard polystyrene for a controlled relative humidity. The methodology proposes a new differential photoacoustic system, including the water reservoir, relative humidity, and temperature detectors. Two cells, reference/sample, were used to obtain the instrumental function to reduce the electronic and environmental noises. A method based on the study of ln[1−(S−S0)/ΔS]=t/τD and the behaviors of R2 as a function of the number of data was proposed to assess the region in which the photoacoustic signal should be processed to determine each effective coefficient. S is the amplitude of the PA signal, S0 is the initial amplitude value, ΔS is the change, t (time), and τD is the water vapor diffusion time. The effective water diffusion coefficient (Deff) for water and polystyrene was 1.90 × 10−11 m2/s and 3.09 × 10−11 m2/s, respectively. The permeability coefficient value for the piece of paper was 4.18 × 10−9 mol kg−1 cm−2 s−1 Pa−1, while for polystyrene, it was 6.80 × 10−9 mol kg−1 cm−2 s−1 Pa−1 for 70% of relative humidity. This methodology can be extended by changing the moisture content on the chamber to obtain the dependence of Deff as a function of relative humidity.

Isothermal Drying Kinetic Study of Spent Coffee Grounds Using Thermogravimetric Analysis

Drying coffee grounds involves high energy consumption and represents an important step in using coffee waste materials as green energy. This study analyzes the drying process using thermogravimetric analysis. The kinetics of the drying process of coffee grounds, containing equal proportions of Arabica and Robusta, were evaluated under isothermal conditions at various temperatures: 50, 60, 70, and 80°C, with sample layer thicknesses of 0.6, 1.2, 1.8, and 2.4 mm. The thermogravimetric curves obtained for the coffee grounds samples under conditions of constant temperature allowed the tracing of the drying curves (moisture content—drying time). The influence of the furnace air velocity on the drying and water evaporation process was analyzed. The drying rate has been established to be about 2.6 times slower than the rate of water evaporation under the same conditions; as a result the overall process is controlled by the effective water diffusion in the layer. This aspect is important in industrial practice for sizing tubular dryers. The activation energy was found to be influenced by the thickness of the coffee grounds layer subjected to the drying process and had values between 8.3 kJ/mol and 10.3 kJ/mol.

Evaluation of ascorbic acid impregnation by ultrasound‐assisted osmotic dehydration in plantain

The objective of this study was to evaluate the impregnation of ascorbic acid (AA) by ultrasound (US)-assisted osmotic dehydration (OD). A 25 factorial design was used. The highest water loss (WL) of 42% was obtained with the combined use of OD+US+AA. The effective diffusivities of water (EDw) and solids (EDs) were increased when OD was employed with a temperature of 60°C, a sucrose concentration of 60%, and a simultaneous application of US+AA treatments in plantain thin slices. The use of OD+US favored AA impregnation; in the treatment with 45% sucrose at 40°C, AA increased from 18% to 42%. Tonality did not change significantly in the OD+US+AA treatments at 40°C. However, except for the gumminess, significant differences from the control were observed in the texture profile analysis (TPA). In microstructure analyses, it was observed that by applying OD+US+AA, the cellular structure was not altered. Applying the specified operational conditions for OD, the AA impregnation pretreatments, and US, a plantain dry food could be obtained without reducing the specified quality parameters in this study. Novelty impact statement Applying the ultrasound pretreatment before osmotic dehydration favors the impregnation of ascorbic acid in the plantain, preserving its original physical and sensory characteristics, such as texture, color, and flavor, and the treatment also promotes the maintenance of the nutritional properties of the food, increases the transfer of mass, and incorporates bioactive compounds.

Foam-mat convective drying of kiwiberry (Actinidia arguta) pulp

The purpose of this work has been to determine the optimal conditions for the processing of kiwiberry fruit pulp based on the relevant thickness of the layer and air temperature, that will target the maximal reduction of drying time and minimal energy consumption. The research was designed to use the response surface methodology (RSM). The effects of independent variables (factors) such as the thickness of the layer (4, 8, and 12 mm) and the temperature of the drying air (50, 60, and 70°C) were studied by the means of the response variables. In this study, the drying kinetics was evaluated based on the drying time, drying rate, and effective water diffusion coefficient (D&lt;sub&gt;eff&lt;/sub&gt;). Based on the simplified Fick's second law of diffusion, D&lt;sub&gt;eff&lt;/sub&gt; was determined, while the relative water content [moisture ratio (MR)] was predicted using empirical models. It was found that as the temperature of the drying process increased, the process time was reduced, and the drying process intensified, which was manifested by the increment of the drying rate as well as the effective moisture diffusivity (varied from 5.58 × 10&lt;sup&gt;–10&lt;/sup&gt; m&lt;sup&gt;2&lt;/sup&gt; s&lt;sup&gt;–1&lt;/sup&gt; to 27.2 × 10&lt;sup&gt;–10&lt;/sup&gt; m&lt;sup&gt;2&lt;/sup&gt; s&lt;sup&gt;–1&lt;/sup&gt;). The mathematical model, developed using the RSM, showed a good fit for the data obtained in the study, which allowed to predict the response of the effective water D&lt;sub&gt;eff&lt;/sub&gt; of the foamed kiwiberry fruit pulp with R&lt;sup&gt;2&lt;/sup&gt; &amp;gt; 0.97.

Fluidized bed roasting of cocoa nibs speeds up processing and favors the formation of pyrazines

Roasting is an important step in cocoa processing causing water loss and generating volatile compounds responsible for chocolate aroma like nitrogen-heterocycles. In this study, the comparison of two techniques, oven roasting, and fluidized bed roasting, in terms of effective water diffusivity (De) and activation energies of formation (Ea) of nitrogen-heterocycles was achieved with cocoa nibs. Fluidized bed roasting, recognized for its energy efficiency and low-footprint synthesis, was 16 times faster than oven roasting. The order of magnitude of De in fluidized-bed-roasted nibs was −8, while it was −9 in the oven-roasted nibs. Moreover, the aw was 50% higher in fluidized-bed-roasted nibs than in the oven-roasted ones. The Ea of nitrogen-heterocycles ranged roughly between 40 and 80 kJ/mol. Those values were lower under fluidized bed roasting than under oven roasting. The more effortless water mobility within fluidized-bed-roasted cocoa demanded lower Ea, and favored the formation of nitrogen-heterocyclics. Industrial relevanceThis study can inspire cocoa manufacturers and equipment designers to pursue the formation of nitrogen-heterocycles during the roasting process of cocoa. It can be done either by adapting and scaling the current fluidized bed coffee roasters to cocoa beans or nibs; or by exploring other alternatives capable of leading enough water diffusivity and water activity in the cocoa nibs, as reported here. These physicochemical conditions undoubtedly boosted the formation of volatile compounds responsible for chocolate aroma, e.g., the pyrazines, without carrying the formation of typical-burn volatile compounds. This natural way of favoring the generation of pyrazines in cocoa nibs could contribute to clean labels by reducing or avoiding the subsequent use of flavorings. The implementation of efficient heat-transfer techniques during roasting, e.g., fluidized bed roasting, could reduce the processing cost and improve sustainability. Studies in the matter of sensory profile, and energy consumption/conversion are called for future research.