Integrated drying model of lychee as a function of temperature and relative humidity

Drying is a universal method applied for food preservation. To date, several models have been developed to evaluate drying kinetics. In this study, lychee was dried employing a hot air dryer, and the drying kinetics was evaluated by comparing the Newtonian model, Henderson and Pabis model, Page model, and Logarithmic model. However, temperature and relative humidity, the key driving forces for drying kinetics, are not considered by these models. Thus, an integrated drying model, as a function of temperature and relative humidity, was developed to predict the hot air-drying kinetics and mass transfer phenomena of lychee followed by the calibration and validation of the model with independent experimental datasets. The model validation consisted of Nash- Sutcliffe model coefficient (E ), coefficient of determination ( R 2 ) and index of agreement ( d ) and all of them were found close to 1 indicating perfect model fit. Besides, the developed model was applied for process optimization and scenario analysis. The drying rate constant was found as a function of temperature and relative humidity that was high at high temperature and low relative humidity. Interestingly, temperature showed a higher effect on the drying rate constant compared to relative humidity. Overall, the present study will open a new window to developing further drying model of lychee to optimize quality its quality parameters.

Comparative evaluation of drying methods for struvite produced from electrocoagulated source-separated urine: Implications for quality, energy and cost-effectiveness

Struvite precipitation from source-separated urine is crucial for waste utilization and sustainability. However, after precipitation, the high moisture content of struvite necessitates an additional drying process that can be costly and inefficient. In the present study, the performance of different drying methods-open sun drying, air drying, conventional drying (20-100 °C), and microwave drying (180-720 W) on the quality of struvite obtained from source-separated urine through electrocoagulation using Mg-Mg electrodes were evaluated. It was found that higher temperatures and power in the convective oven and microwave resulted in higher diffusivity (10-9-10-7 m2s-1), leading to reduced drying times. Different models were employed to comprehend the drying mechanism, and the one with the highest correlation coefficient (R2 = 0.99) and the lowest statistical values was selected. The key findings indicated that higher power and temperature levels were more cost-effective. However, characterization of the dried struvite using X-ray diffraction and Fourier-transformed infrared spectroscopy, disintegration of struvite crystals at temperatures above 60 °C in the conventional oven and 180 W in the microwave oven was observed. Based on the results, we conclude that sun drying is a cost-effective and environmentally friendly alternative for drying struvite without compromising its quality.

Thermal performance study of a PV-driven innovative solar dryer with and without sensible heat storage for drying of Garcinia Pedunculata

Uneven drying is the key drawback of a conventional multi-tray dryer. Therefore, an improved active solar dryer with and without integrated sensible heat storage (SHS) was proposed. A unique feature of this dryer is its movable walls from the sides of the dryer to transform it to an indirect or mixed-mode as and when necessary. Garcinia Pedunculata (GP) is a local seasonal medicinal fruit in Northeast India. Drying kinetics of GP, the dryer performance and economic analysis of dryer were evaluated in the indirect solar dryer without SHS (Exp. I), mixed-mode solar dryer without SHS (Exp. II), indirect solar dryer with SHS (Exp. III), mixed-mode solar dryer with SHS (Exp. IV), and open sun drying (OSD). The dryer's average efficiencies were 18.12%, 22.37%, 21.74%, and 24.46% for Exp. I, Exp. II, Exp. III, and Exp. IV, respectively. The moisture content of GP was reduced to 12.09% in wet basis (w.b.) from 87.99% (w.b.). The overall drying time for Exp. I, Exp. II, OSD, Exp. III and Exp. IV were 31, 26, 53, 28, and 10 h, respectively. From the eleven drying models, the Two-Term model was the best-fitted model for Exp. I, Exp. II, OSD and Exp. III, and Midilli and Kucuk model was for Exp. IV. The final product's fragrance and colour are better for Exp. IV. Developing this dryer for Exp. I, Exp. II, Exp. III and Exp. IV, the price required was around 25,000, 27,000, 26,000, and 28,000 INR (1 US$ = 74.57 INR), respectively, while the economic payback periods are 1.6 years, 0.9 year, 1.4 years, and 0.59 year, respectively.

Experimental investigation of modified indirect solar dryer with integrated thermal storage material for drying of dhekia (Diplazium esculentum) fern

Food product drying is a crucial stage in the preservation of crops and agricultural by-products that are used as raw materials for numerous end applications. The novelty of the study is the application of a phase change material in a solar dryer to improve the effectiveness of drying and reducing the overall drying period for drying while retaining/improving the quality parameters of the dried dhekia (Diplazium esculentum). The modified indirect thermal storage integrated solar dryer made up of a single-pass solar collector is attached with the drying chamber of 16.5 kg capacity. A thermal energy storage system prepared with paraffin wax embedded inside the drying cabinet was used. The proposed solar dryer has a thermal efficiency that is 11 ± 0.2% greater than the conventionally constructed solar dryer and reduces drying time by 40 ± 2.1%. Drying kinetic analysis of dhekia was performed, and two new drying kinetic models were proposed to predict moisture ratio. From statistical analysis, it was found that the chi square value and root mean square error value fits well for the proposed models. The anti-oxidant, total phenolic content, and total flavonoid content values of samples dried in solar dryer exhibit better results compared to fresh, tray dried, and open sun-dried samples. The developed dryer shows better results in saving drying time and quality of the product. Due to its affordability and long-term solution for drying fresh farm goods, this dryer can be very helpful to small-scale farmers.

Convective drying of Gardenia erubescens fruits: Effect of pretreatment, slice thickness and drying air temperature on drying kinetics and product quality

Gardenia erubescens fruits are regarded as nutrient-dense, capable of promoting nutritional and metabolic human health. However, they are seasonal and highly perishable which limits their consumption and wider utilization. In this study, the effect of slice thickness (3 mm and 5 mm), pretreatments (steam blanching and dipping in ascorbic acid solution) and drying air temperature (40 °C, 50 °C, 60 °C and 70 °C) on drying kinetics, color, β-carotene and vitamin C content of Gardenia erubescens fruits were investigated. The results showed that the drying time increased as slice thickness increased, and decreased as drying air temperature increased but did not follow any trend for pretreatment. The Page model (R2 values of 0.9998-0.9999) exhibited the best fit to the drying kinetics data. The diffusivity values (5.31 × 10-11 to 4.14 × 10-10 m2s-1) increased as the slice thickness and drying air temperature increased but had no linear trends with pretreatment. The activation energy ranged from 14.35 to 44.78 kJmol-1, with the highest being recorded by 5 mm untreated samples and the lowest by the 3 mm blanched samples. The total color change (ΔE*) of the samples generally decreased as the drying air temperature increased but increased as the slice thickness increased. The ascorbic acid pretreated samples had the least color change, followed by the untreated samples while the blanched samples had the highest change. Overall, the 5 mm ascorbic acid pretreated samples dried at 70 °C had the least color change (13.33 ± 0.52). The blanching and dipping in ascorbic acid solution generally yielded lower β-carotene and vitamin C values as compared to the untreated samples. The 3 mm ascorbic acid pretreated samples dried at 50 °C recorded the lowest β-carotene (42.70 ± 3.21 μg/100 g) while the 5 mm ascorbic acid pretreated samples had the lowest vitamin C (37.50 ± 2.65 mg/100 g) at 70 °C. Pretreatments and drying air temperatures showed mixed effects on the drying characteristics, color, β-carotene and vitamin C contents of fruit slices. The findings, therefore, indicate that a compromise may have to be made on the aforementioned processing conditions in order to meet the desired attributes of one's interest.

Drying strategies of spent coffee grounds using refractance window method

The objective of this study was to evaluate, during the drying of spent coffee grounds, the application of pretreatments with ethanol and the application of ultrasound assisting the refractive window (RW) drying, and to compare with convective drying by hot air (AC). The effect on the kinetics parameters of the Fick and Page models were evaluated, as well as on the content of total phenolics and antioxidant capacity. For AC drying, samples of spent ground coffee were prepared in the form of fixed rectangular beds 0.7 cm high, which were placed on polyester sheets and pretreated up to 10 times sprayed with ethanol, then dried by AC at 80 °C and 0.8 m/s. For RW drying, the samples prepared in the same way as for AC were used. For this case, the application of ethanol as pretreatment and the use of ultrasound during process were tested. As results, regardless of the conditions applied, drying by RW was up to 50 % faster, evidenced in the highest values of effective diffusivity (from the Fick model) and the kinetic parameter (from the Page model). Regarding the treatments applied and their effect on the drying kinetics, any treatment had a significant effect on AC drying. On the contrary, the strategies applied in RW drying had significant effects, both the application of pretreatment with ethanol as well as the application of ultrasound assisting the process accelerated the drying kinetics. However, the treatment with ethanol and RW drying was the one that best preserved the phenolic compounds and the antioxidant capacity in the samples. Therefore, these strategies could be a good option to improve RW drying by accelerating the process and preserving the bioactive compounds in the spent coffee grounds for subsequent utilization.

Oyster mushroom drying in tray dryer: Parameter optimization using response surface methodology, drying kinetics, and characterization

In this study, the drying of oyster mushrooms (P. ostreatus) in a tray dryer was optimized. The parameters used to optimize the drying process were drying temperature, airspeed, mass loading, and moisture content. Its drying kinetics were investigated at the optimum drying parameters. A quadratic equation was obtained to predict the moisture content of mushrooms at the given drying temperature, airspeed, and mass loading, and it was validated against experimental results. A minimum moisture content (9.99 wt%) was obtained at the optimum conditions of 60 °C, 3 m/s airspeed, and mass loading of 200 g using a tray dryer. Proximate analysis, shelf-life analysis, inorganic elemental analysis, and functional group analysis were done as a characterization method for mushrooms after drying at the optimum drying conditions. About 27.8 wt% protein and 50.2 wt% carbohydrates were found in proximate results. Besides, potassium and sodium were the dominant elements as estimated by spectrophotometry analysis. The induction period (IP) of dried mushrooms at room temperature is 3520:47 (hour: minute) from the oxidation stability analysis, and the water activity of dried mushrooms was found to be 0.36. The drying kinetics of oyster mushrooms were studied at various temperatures (50-75 °C), optimum airspeed (3 m/s), and mass loading (200 g). The best-fit model describing the mushrooms drying kinetics was found to be Midilli et al., with the lowest RMSE (0.008749), X2 (0.0014), and the highest R2(0.9993) values. The kinetic triplet activation energy, effective diffusivity, and diffusivity constant (Ea, Deff, D0) for oyster mushrooms drying were determined and found to lay in the general range for foodstuffs. The value of Deff results lies within the range of 10-8 to 10-12 m2/s, with Ea of 15.32 kJ/mol and D0 value 2.263 × 10-6 m2/s.

Experimental determination of dynamic pseudo-equilibrium moisture content: A practical limit for the drying process

Simulation and rigorous design of industrial dryers combine a large number of models, which feed three fundamental balances: (1) mass; (2) energy; and (3) quantity of movement of the material through the dryer. Many of these models represent physical phenomena affecting the three balances at the same time, which makes these calculations extremely complex, hence, accurate models are essential. The hypothesis that the kinetic stage of drying of any material culminates in the thermodynamic moisture equilibrium between solid and drying gas has been in effect for many years. However, recent findings show that there is a transition stage between the kinetic stage and the thermodynamic equilibrium, which, experimentally, looks like an equilibrium. The beginning of this transition stage or dynamic pseudo-equilibrium stage would mark the end of the drying kinetics models, which has been named as the dynamic pseudo-equilibrium moisture contents (Xdpe). The non-observance of this phenomenon presupposes a model limited in its prediction capacity, especially in the last stages of drying and even more so at low drying temperatures. As a consequence, sizes of industrial dryers could be underestimated during the simulation and rigorous design process, or underestimate drying times, in batch dryers. On the other hand, the optimal conditions may never be found, during the optimization of existing industrial drying processes. The objective of this work is to present the procedure to determine Xdpe, during the experimental determination of drying curves of any material. Likewise, to propose the practical moisture ratio, which uses Xdpe, instead of the equilibrium moisture, to be used in the modeling of the drying kinetics.•The drying process is divided into three stages: kinetic, transition, and equilibrium.•The dynamic pseudo-equilibrium moisture content divides the kinetic and the transition stages.•The practical moisture ratio should be used in rigorous industrial dryer design calculations.

Ultrasonic pre-treatment to enhance drying of potentially probiotic guava (Psidium guajava): Impact on drying kinetics, Lacticaseibacillus rhamnosus GG viability, and functional quality

This study aimed to evaluate the effects of ultrasound (US) on the drying acceleration of potentially probiotic guava, including its impact on drying kinetics, probiotic (Lacticaseibacillus rhamnosus GG) viability, and functional quality of the product during drying. To perform US pre-treatments, one group of samples were first pre-treated by US (38 W/L, 25 kHz) for 15 and 30 min and then immersed in the probiotic solution for 15 or 30 min, and another group of samples were submerged in the probiotic solution simultaneously applying US (US-assisted) for 15 and 30 min. After pre-treatments, the samples were convectively dried at 60 °C. Based on the results, all US pre-treatments improved the drying rate (up to 59%) and reduced the drying time (up to 31%) to reach 25% moisture compared to non-sonicated samples. The reduction in drying time (from ∼6 h to ∼4 h for US pre-treated samples) was crucial for maintaining the probiotic viability in the dehydrated guavas. These samples showed counts of 6.15 to 7.00 CFU∙g-1 after 4 h, while the control samples reached counts of 4.17 to 4.45 CFU∙g-1 after 6 h. US pre-treatment did not affect the color parameters of the samples before drying (p > 0.05). The functional compounds were reduced during drying (p < 0.05), however, all US pre-treated samples had lower reductions in vitamin C content (up to 20%), phenolic compounds (up to 41%) and antioxidant capacity (up to 47%) compared to control samples (up to 52%, 81% and 61%, respectively). Therefore, US pre-treatment (highlighting the US-assisted probiotic incorporation for 30 min) reduced the drying time for guava slices and minimized the thermal impact on probiotic viability and functional compounds, being a strategy to produce potentially probiotic dehydrated guava.

Dried grape pomace with lactic acid bacteria as a potential source for probiotic and antidiabetic value-added powders

Two drying methods (convective (CD) and infrared (IR)) on grape pomace with probiotics were analysed, based on kinetic models and survival rate. The moisture ratio decreases linearly with drying time. The IR drying time reduced up to 14.3% at 50 °C. The Page model allowed to calculate the drying constant (0.188-0.404 s-1), whereas the effective moisture diffusivity ranged from 6.64 × 10-9 to 9.38 × 10-9 m2/s for CD and from 8.83 × 10-9 to 11.16 × 10-9 m2/s for IR, respectively. Chromatographic analysis highlighted the presence of 28 anthocyanins, with cyanidin-3-O-monoglucoside as a main bioactive in both powder. The probiotic survivale rate reached 7.0 log CFU/g dry weight after 14 days of storage at 4 °C. The extracts affected conformation of α-amylase, with binding constants lower for IR extract (15.94 ± 1.61 × 10-2 Mol/L) when compared with CD (25.09 ± 2.14 × 10-2 Mol/L). The IC50 values were significant higher for the IR (6.92 ± 0.09 μMol C3G/mL) when compared with CD extract (10.70 ± 0.12 μMol C3G/mL).

Combined osmotic pretreatment and hot air drying: Evaluation of drying kinetics and quality parameters of adajamir (Citrus assamensis)

Adajamir (Citrus assamensis) is a highly perishable but nutritional fruit. Hot air drying is ubiquitous in food preservation but not quality friendly. However, drying pretreatments play an indispensable role preserving fruits and vegetables. The aim of this study was, therefore, to reveal the hot air drying kinetics of osmotically pretreateated adajamir and investigate the quality parameters (total phenolic contents, antioxidant capacity, and vitamin C). Adajamir slices were subjected to osmotic pretreatment (10% sucrose, 10% fructose, and 2% NaCl), subsequently, dried in a hot air dryer at 50 °C, 30% relative humidity (RH), and with a velocity of 1 ms-1. The drying kinetics were studied using three mathematical models: Newtonian model, Henderson and Pabis model, and Page model. The result depicted that effective diffusivity was highest (9.5 ± 0.2a × 10-6 m2s-1) in untreated samples compared to the treated samples, and the Page model was the one with the best fitness to explain the drying behavior. Regarding quality, the pretreatments provided better retention of all quality parameters compared to the untreated samples. In addition, osmotic treatment with sucrose had the best quality retention capability. The study will contribute to the optimization of thermal processing parameters in fruit dehydration. Eventually, this research will expedite future research pertinent to innovative combined drying techniques of citrus fruit.

Drying kinetics and quality dynamics of ultrasound-assisted dried selenium-enriched germinated black rice

Black rice is a functional food due to its higher protein, fiber, iron, antioxidant compounds, and other health benefits than traditional rice. The ultrasonic (US) pretreatments (10, 20, and 50 min) followed by hot-air drying (50, 60, and 70 °C) were applied to study the drying kinetics, mathematical modeling, thermodynamics, microstructure, bioactive profile, volatile compounds and to lock the nutritional composition of selenium-enriched germinated black rice (SeGBR). Ultrasonic-treated samples exhibited a 20.5% reduced drying time than control ones. The Hii model accurately describes the drying kinetics of SeGBR with the highest R2 (>0.997 to 1.00) among the fifteen studied models. The activation energy values in US-SeGBR varied from 3.97 to 13.90 kJ/mol, while the specific energy consumption ranged from 6.45 to 12.32 kWh/kg, which was lower than untreated. The obtained thermodynamic attributes of dried black rice revealed that the process was endothermic and non-spontaneous. Gallic acid, kaempferol, and cyanidin 3-glucoside were present in high concentrations in phenolics, flavonoids, and anthocyanins, respectively. The HS-SPME-GC-MS investigation detected and quantified 55 volatile compounds. The US-treated SeGBR had more volatile compounds, which may stimulate the release of more flavorful substances. The scanning electronic micrograph shows that the US-treated samples absorbed high water through several micro-cavities. Selenium concentration was significantly higher in US-treated samples at 50 °C than in control samples. In conclusion, ultrasound-assisted hot-air drying accelerated drying and improved SeGBR quality, which is crucial for the food industry and global promotion of this healthiest rice variety.

Impact of electrolyzed water as pre-treatments on drying properties and total colour difference of fresh-cut 'Tommy Atkins' mangoes

Mango fruits are a rich source of nutrients, however, due to their perishability and seasonality, minimal processing and drying offer the potential ensure a shelf stable and safe product. The use of sodium metabisulphite (SMB) as pre-treatment in the dried fruit industry has been widely adopted, but sulphite residue remains a health public concern. Therefore, this study investigated the effects of alkaline and acidic electrolyzed water (AIEW and AEW, mg/mL) as alternative pre-treatments to SMB (1% w/w) for 'Tommy Atkins' mango slices prior to hot air drying at 60 °C. Fresh-cut and untreated samples were used as a control. During the drying process the weight of the slices were monitored every 60 min for 10 h, which was used to calculate moisture ratio (MR), drying rate (DR), and the experimental data of the samples were subjected to eight thin layer models. Colour parameters (L*, a*, and b*) were measured, and use to determine colour intensity (C*), hue angle (h°), and total colour difference (TCD) before and after drying. Based on measured weight, continuous decline in MR was recorded for all dried mango slices over the drying time irrespective on treatment. Out of the eight applied thin layer models Henderson & Pabis and Logarithmic were the best appropriate models describing and predicting the drying behavior of 'Tommy Atkins' mangoes (R2 = 0.94, RMSE ≥ 0.0006). Samples treated with AEW treated samples had lowest L*, h°, and TCD values (p < 0.05). No significant different were found in h° values amongst all pre-treated and dried samples (p > 0.05), but these samples were significantly different from dried untreated (control) and fresh samples (p < 0.05). Pre-treatments maintained the visual quality of dried 'Tommy Atkins' mango slices; SMB > AIEW > AEW > untreated (control). This study provided science-based evidence for the application of acidic and alkaline electrolyzed water as an alternative pre-treatment to sodium metabisulphite for the drying of 'Tommy Atkins' mango.

Effective moisture diffusivity prediction in two Portuguese fruit cultivars (Bravo de Esmolfe apple and Madeira banana) using drying kinetics data

Air convective dehydration was performed at various temperatures (35 °C, 40 °C, 45 °C and 50 °C) using two types of fruits cultivars produced in different regions of Portugal: the Bravo de Esmolfe apple, from the Beiras province, and the Cavendish banana, from Madeira Island. The data collected were used to predict the effective moisture diffusion, which is a crucial input parameter in drying modeling and design. As expected, the values obtained in both falling drying rate periods detected for apples increased with an increase in drying temperature. The effective moisture diffusion in apples varied from 1.968 × 10^-10 m² s^-1 at 35 °C to 4.013 × 10^-10 m² s^-1 at 50 °C, for the first falling drying rate period, and from 0.9567 × 10^-10 m² s^-1 at 35 °C to 3.328 × 10^-10 m² s^-1 at 50 °C, for the second period. The dependence of effective moisture diffusion on temperature for bananas is similar, ranging from 1.572 × 10^-10 to 2.627 × 10^-10 m² s^-1 as the drying temperature changed from 35 to 50 °C.

Drying kinetics and economic analysis of bitter gourd flakes drying inside hybrid greenhouse dryer

In this study, a heat storage-based hybrid greenhouse dryer has been developed and analysed for drying bitter gourd flakes under the climatic condition of Ranchi, India. Proposed heat storage-based hybrid greenhouse dryer consists of a solar air heater with a 2.12-m² area, greenhouse dryer and DC fan to induce and force the air. The significant objective of the present study is to analyse the drying efficiency, drying kinetics, property analysis, economic analysis, embodied energy and CO₂ mitigation of the hybrid greenhouse dryer for drying of bitter gourd flakes. An experiment was performed simultaneously on proposed system and open sun drying for the proper comparative analysis. Moisture contents reduced from 88.14 to 10.14% in 6 h in proposed dryer and 88.14 to 11.01% in 15 h for open system. Thus, significant drying time is reduced in proposed system by 8 h as compared to open system. Environmental impact analysis shows that the energy payback time was found to be 0.4907 years only. Cost of the proposed system dryer is 22664.30 INR. The total embodied energy is found 1591.07 kWh and earned carbon credit ranges from 16844.76 to 67379.05 INR, while CO₂ mitigation was 46.28 tonnes for 35 years of expected lifetime. Seven standard mathematical models for drying of bitter gourd flakes were studied. Ahmad and Prakash model was found to be the best as compared to other models. The metal contents of dried bitter gourd flakes were also examined. Bitter gourd dried in proposed dryers possesses superior metal content as compared to open systems. Impact analysis demonstrates that the hybrid greenhouse dryer is more suitable for reducing post-harvest loss with environmental sustainability.

Experimental investigation and energy-exergy-environmental-economic analysis of modified indirect solar dual collector dryer while drying myrobalan slices

The paper presents the performance evaluation of a modified indirect solar dual collector dryer (MIS2CD) integrated with a thermal storage system for drying myrobalan slices. The design of the solar collector and solar collector with thermal storage was to supply uninterrupted thermal energy to the drying chamber during sunny and sunset hours. To evaluate the dryer performances, one lot (20 kg) of myrobalan was dried in the MIS2CD, and as a result, the thermal efficiency and energy supply period of MIS2CD increased by 12 ± 02% and 41 ± 1.2%, respectively. Drying characteristics of myrobalan slices in MIS2CD, TD, and OSD were studied and compared. A two-term exponential model best explains the drying kinetics of myrobalan slices dried in MIS2CD. The dried sample in MIS2CD results in lesser ΔE* values than TD and OSD methods. The highest exergy efficiency of 78.2% and lower exergy losses were recorded. The energy payback period of the MIS2CD was evaluated as 1.42 years. The CO₂ emitted and CO₂ reduced reduction are calculated for drying myrobalan in MIS2CD for a lifetime (20 years) of 67.85 kg and 20.65 tons, respectively. The capital cost of the solar dryer design was estimated depending on the economic considerations of the state. The drying hours were increased in MIS2CD against OSD by 59% on the annual sunny days (210 days). The sample drying period MSD and TD to reach the final moisture level of 7% was 9 h and 5 h, respectively. The total economic benefit is 22,622 INR (annually), and the 2.08 benefit-cost ratio for myrobalan dried in MIS2CD compared to TD. The MIS2CD's payback period is nearly 2.18 years, much less than the dryer's lifetime.

Effect of dielectric barrier discharge (DBD) cold plasma-activated water pre-treatment on the drying properties, kinetic parameters, and physicochemical and functional properties of Centella asiatica leaves

Centella asiatica L. (CA) is a medicinal plant that gained significant commercial and research interest because of its bioactive compounds, which have functional properties such as antioxidant activity. However, it must be dried before use to improve its shelf life and prepare it for food and pharmaceutical applications. Therefore, in this investigation CA leaves were pre-treated with blanching and cold plasma activated water (CPAW), followed by recirculatory hot air and vacuum drying at 40, 50, and 60 °C. Vacuum-drying took 150-720 min, while hot-air drying took 60-180 min to dry. Page and Logarithmic models best fit for leaf drying kinetics, according to AIC, with R² between 0.966 and 0.999 and RMSE between 0.001 and 0.069. CPAW pre-treatment increased leaf quality more than blanching in vacuum drying. Drying leaves at 40 °C boosted antioxidants (4021.462 μg TE (g dw)^-1 and 3.356 mg GAEAC (g dw)^-1), TPC (35.049 mg GAE (g dw)^-1), and TFC (311.274 mg QE (g dw)^-1) and is recommended. Vacuum-drying with CPAW pre-treatment preserved leaf microstructure better than hot-air drying. This study illuminates CA leaf drying behaviour and allow mass production without damaging bioactive components. These results could be used as a roadmap for future technological advances that will make it possible to use the bioactive components of CA in food formulation.

Influence of meat sample geometry on dehydration dynamics during dry-aging of beef

Meat geometry may impact on the dehydration kinetics during dry-aging influencing the drying rate and, potentially, aspects of meat quality. In this study, three meat geometries (slices, steaks and sections) were prepared from three bovine Longissimuss thoracis et lumborum at 3 days post-mortem and were dry-aged at 2 °C, 75% relative humidity with an airflow of 0.5-2.0 m/s for 22 days (slices), 48 days (sections) and 49 days (steaks). Weights were recorded during dry-aging and drying curves were obtained for the three geometries, with the larger sections showing limited dehydration due to internal resistance to moisture migration from the core to the surface. Seven thin-layer equations were fitted to the dehydration data in order to model the drying kinetics during dry-aging. Thin-layer models described reliably the drying kinetics of the three geometries. In general, reduced k values (h^-1) reflected the lower drying rates as thickness increased. The Midilli model provided the best fit for all geometries. Proximate analyses of the three geometries and bloomed colour of sections were measured at the start and the end of the dry-aging period. Moisture loss during dry-aging led to the concentration of protein, fat and ash contents; while no significant differences were found for L*, a* and b* values of sections before and after the dry-aging process. In addition, moisture content, water activity (a_w) and LF-NMR measurements were taken at different locations within beef sections to further explore water dynamics during dry-aging.

Drying kinetics and attributes of fructus aurantii processed by hot air thin-layer drying at different temperatures

The primary objectives of this study were to evaluate the drying kinetics of Fructus Aurantii (FA), and to investigate how hot air drying at various temperatures affected the surface texture and sensory quality of the volatile fragrance components. The results were best simulated by the Overhults model, and use of scanning electron microscopy (SEM) and Heracles Neo ultra-fast gas phase electronic nose technology allowed for detection of changes in surface roughness and aromatic odors. The limonene content varied from 74.1% to 84.2% depending on the drying temperature, which ranged from 35°C to 75 °C. Furthermore, principal component analysis (PCA) revealed that the aromatic compound profile underwent considerable changes during the drying process. Overall, the present findings demonstrate that hot air thin-layer drying at 55 °C can significantly enhance the final quality of FA while preserving the taste properties and providing optimum medicinal and culinary characteristics.

Analysis and comparison of the performance parameters of passive and active indirect solar dryers with heat storage facility while drying carrot

The performance of passive and active convection indirect solar drying systems provisioned with paraffin wax as heat storage was examined while drying carrot slices. The passive indirect solar dryer (type-I) was made initially, and it was upgraded with solar-powered fans to promote mass flow rate. The new assembly was considered an active setup (type-II). Data collected during experiments were analyzed to determine performance parameters and drying kinetics. There were average improvements of 11.8%, 12.2%, and 20.7% in actual heat supply, activation energy, and specific energy consumption in type-II compared to type-I. The averaged values of collector efficiency of type-I and type-II were 59.7 and 67.8%, and the drying efficiency was 11.1 and 14.2%, respectively, while their respective improvements were 13.6 and 27.93%. It was found that the coefficients of moisture diffusion (D_e), heat transfer (h), mass transfer (h_m), and the rate of specific moisture extraction were increased by 20.83%, 16.9%, 14.52%, and 27.8%, respectively in type-II compared to type-I. A logarithmic correlation was observed for D_e, h, and h_m demonstrating a decrease in moisture content (MC) increased the variables. The MC was diminished from 9.13 to 0.478 kg/kg of db in 15 h in type-I and 12 h in type-II with a 3 h saving in drying time with a better drying rate in type-II. The reliability of the results was assessed with uncertainty analysis.

Effect of ohmic blanching on drying kinetics, physicochemical and functional properties of garlic powder

This study aims to perform an optimization of process parameter for ohmic blanching of garlic to focus on the drying characteristics of the garlic powder at different temperatures. Comparative analyses on physicochemical and functional properties of differentially blanched garlic powder are carried out. The browning intensity was found to be lesser in garlic with ohmically blanched at 26.66 V/cm for 30 s. Process optimization was carried using different thin layer models, out of which Midilli-Kucuck was found to best fit model (R 2 = 0.9954). Rate of drying was significantly higher in ohmically blanched garlic compared to conventional blanching. Obtained garlic powder by differential blanching methods was analyzed for physicochemical and functional attributes specifically; diallyl disulphide content was retained up to 945.8 mg/kg, 928.7 mg/kg and 667.6 mg/kg, respectively.

Based on quality, energy consumption selecting optimal drying methods of mango slices and kinetics modelling

Mangoes have a short shelf life because of their high-water content. This study aimed to compare the effect of three drying methods (HAD, FIRD and VFD) on mango slices to improve product quality and reduce costs. Mangoes were dried at various temperatures (50, 60, 70 °C) with different slice thicknesses (3, 5, 7, 10 mm). Results indicated that FIRD was the most cost-effective with the dried mango containing the highest sugar-acid ratio, and when the mango slices thickness was 7 mm and drying at 70 °C, the ascorbic acid content, rehydration ratio, sugar-acid ratio, and energy consumption per unit volume reached 56.84 ± 2.38 mg/100 g, 2.41 ± 0.05, 83.87 ± 2.14, and 0.53 kWh/L. Among three mathematical models, the Page model described the most satisfactory drying behaviour of mango slices in FIRD. This study provides useful information in mango processing industry and FIRD is supposed to be a promising drying method.

Drying kinetics and thermo-economic analysis of drying hot water blanched ginger rhizomes in a hybrid composite solar dryer with heat exchanger

This research aimed to examine the need of adding hot water blanching pre-treatment on the drying of ginger rhizomes using a hybrid solar-dryer with paraffin liquid as thermal storage infused into a copper tube to form a compact heat exchanger. Blanching duration quickened the drying rate of the ginger rhizomes and the average drying rate for blanching at 90 s, 60 s, 30 s and un-blanched ginger varied between 0.0147 kg/h to 0.0245 kg/h at a sensible heat ratio of 4.12 × 10^-5 to 2.53 × 10^-3. The optimal drying rate varied from 0.01161 kg/h to 0.0263 kg/h for all treatment at a collector temperature range of 39.5 °C-40.5 °C and collector efficiency range of 14.3%-30%. The logarithmic model better predicted the drying kinetics of un-blanched and blanching for 30 s with an R² value of 0.9875 and 0.97247 respectively while the modified Henderson and Pabis model better predicted drying of blanched ginger rhizomes at 60 s and 90 s with R² values of 0.96252 and 0.98188 respectively. Using the hybrid solar dryer instead of artificial dryers with fossil energy sources can save about $75.731 to $757.31 of the running cost as the usage increased from 10 to 100%. The payback period decreased from 2.88 years to 0.31 years as the rate of usage increased from 10 to 100%. Using the presented solar dryer instead of coal, diesel or grid base electricity can prevent 15.96 to 186, 7.62 tones of CO₂ from entering the atmosphere. The earned carbon credit if the dryer is to be powered by coal, diesel or grid base electricity were $ $6245364, $27080.52, and $231.45 per year respectively which can be used to compensate other non-renewable energy sources deployed within an energy enterprise.

Drying of Chinese medicine residues (CMR) by hot air for potential utilization as renewable fuels: drying behaviors, effective moisture diffusivity, and pollutant emissions

High moisture in Chinese medicine residues (CMR) can decrease the energy efficiency of thermochemical conversion, which necessitates the pre-drying. Owing to the complex constituents and decoction, CMR may possess distinct drying characteristics. It is necessary to understand its drying behaviors, effective moisture diffusivity, and pollutant emissions for future design and optimization of an industrial-level dryer. In this study, the drying of four types of typical CMR in hot nitrogen was performed. Their condensate and exhaust gas were collected and characterized. The results indicated that their drying process was dominated by internal moisture transport mechanism with a long falling rate stage. Drying temperature influenced their drying process more greatly than N2 velocity did. Residual sum of squares, root mean square error, and coefficient of determination indicated that Weibull model demonstrated their drying process best. Their effective moisture diffusivity was in the range of 1.224 × 10-8 to 4.868 × 10-8 m2/s, while their drying activation energy ranged from 16.93 to 30.39 kJ/mol. The acidic condensate had high chemical oxygen demand and total nitrogen concentration and yet low total phosphorus concentration. The concentration of total volatile organic compounds, non-methane hydrocarbons, H2S, and NH3 in the exhaust gas met the national emission limitation, while the deodorization of exhaust gas was required to remove odor smell.

Supplementary information

The online version contains supplementary material available at 10.1007/s13399-022-03722-4.

Individual and interactive effect of ultrasound pre-treatment on drying kinetics and biochemical qualities of food: A critical review

One of the earliest and most prevalent processing methods to increase the shelf-life of foods is drying. In recent years, there has been an increased demand to improve product quality while lowering processing times, expenses, and energy usage in the drying process. Pre-treatments are therefore effectively used before drying to enhance heat and mass transfer, increase drying efficiency, and lessen degradation of final product quality. When food is dried, changes are expected in its taste, color, texture, and physical, chemical, and microbial properties. This has led to the need for research and development into the creation of new and effective pre-treatment technologies including high-pressure processing, pulsed electric field, ultraviolet irradiation, and ultrasound. Sound waves that have a frequency >20 kHz, which is above the upper limit of the audible frequency range, are referred to as "ultrasound". Ultrasonication (US) is a non-thermal technology, that has mechanical, cavitational, and sponge effects on food materials. Ultrasound pre-treatment enhances the drying characteristics by producing microchannels in the food tissue, facilitating internal moisture diffusion in the finished product, and lowering the barrier to water migration. The goal of ultrasound pre-treatment is to save processing time, conserve energy, and enhance the quality, safety, and shelf-life of food products. This study presents a comprehensive overview of the fundamentals of ultrasound, its mechanism, and how the individual effects of ultrasonic pre-treatment and the interactive effects of ultrasound-assisted technologies affect the drying kinetics, bioactive components, color, textural, and sensory qualities of food. The difficulties that can arise when using ultrasound technology as a drying pretreatment approach, such as inadequate management of heat, the employment of ultrasound at a limited frequency, and the generation of free radicals, have also been explained.

Current trends in cacti drying processes and their effects on cellulose and mucilage from two Colombian cactus species

The effect of temperature and drying technologies on mucilage and cellulose (obtained by the microwave-assisted extraction technique, MAE) from Opuntia ficus-indica (OFI) and Austrocylindropuntia cylindrica (CC) was determined using a conventional oven (CO) and Refractive Window (RW). Mathematical modeling was performed from drying kinetics data using the Lewis, Henderson-Pabis, Page, and Logarithmic models. Activation Energy (Ea) and Diffusivity (D) were also determined. The model with the best fit was the logarithmic one, with a correlation coefficient (R²) greater than 0.99. The obtained activation energies were 22.81 kJ mol^-1 for Refractance window (RW) and 31.44 kJ mol^-1 using conventional hot air drying (CO) while a diffusivity of 2.9 ∗10^-8 m² s^-1 for RW and 1.3∗10^-8 m² s^-1 for CO were found as well. According to our results, a greater drying efficiency and a less chemical deterioration of the plant sample are obtained by drying with Refractance window.

Influence of foam mat drying on the nutritional and technological potential of fruits - a review

The consumption of fruits and vegetables is strongly encouraged in the nutritional recommendations presented in national and international guidelines, which strongly advise the intake of these elements as part of a healthy diet. However, this type of food matrix has a low post-harvest durability, making it necessary to apply techniques that extend its shelf life. Among the methods that can be applied, drying acts as a unitary operation of wide use, presenting low operational cost, ease of handling and wide variation of procedural techniques. However, it still remains a methodology seen as "critical" in the food sector, especially when the maximum focus of efforts is to obtain a material of high quality, nutritional and sensorial. In this context, foam layer drying has gained recognition as an effective and low-cost technique, where foam porosity and higher surface area-volume ratio provide high heat and mass transfer rates, reducing process time and improving the physical-chemical quality of the final product. We provide information capable of elucidating that drying requires a large amount of energy for the operation, and that many studies are still needed in order to optimize the process and guarantee the economic, nutritional and functional viability of the final product.

Effect of gum Arabic and ethanol pretreatments on drying kinetics and quality attributes of dried carrot slices

Carrot is an important root vegetable to the food industry and consumers due to its nutritional and health benefits. Given the high moisture content and low shelf life of fresh carrots, preserving this highly demanded vegetable is vital. This current research modelled the drying kinetics and evaluated the quality of ultrasonic-assisted gum Arabic and ethanol pretreated and oven-dried carrot slices. Fresh carrots were processed into thin slices and immersed in 3% gum Arabic (GA), ethanol (99.9%), and distilled water (control), followed by ultrasonication (frequency: 50 Hz, power: 500 W, temperature: 25 °C) for 10 min and drying in a hot air oven at 50 °C. The loss of moisture from the carrots was periodically recorded, converted to moisture ratio before fitted to eleven semi-theoretical thin layer drying mathematical models. The effects of the pretreatments on the retention of bioactive compounds and carrots' physical and chemical properties were also evaluated. From the tested models, the Diffusion, Modified Henderson and Pabis, and Two-term models showed the best fitting (R² = 0.9944-0.9985; RSME = 0.0103-0.0227) to the experimental data from 3% GA and ethanol pretreated carrots, while control samples followed the Aghbasho model (R² = 0.9999; RMSE = 0.0033). Overall, the 3% GA pretreated carrot slices exhibited better colour (yellowness: 25.82-34.50; total colour differences: 8.12-13.06), water activity (0.37-0.44), total phenolic content (1.34-2.99 mg GAE/100 g DM), β-carotene (7.63-13.07 mg/100 g DM), and DPPH radical scavenging activity (5.67-8.02 mM AAE/100 g DM) than ethanol pretreated carrot slices and control samples. At the same time, 3 % GA pretreatment did not affect the drying rate of the carrot slices. The total soluble solids/titratable acidity ratio, rehydration capacity, and shrinkage ratio did not significantly (p > 0.05) vary among the treatments. The findings of this study can be used to develop an optimal drying protocol for pretreated carrot slices and to produce shelf-stable carrot products that can be used dried, rehydrated, or in combination with other products.

Evaluation of ultrasonication and carbonation-ultrasonication assisted convective drying techniques for enhancing the drying rates and quality parameters of ripe and raw banana (Musa) peel

Raw and ripe banana (Musa Cavendish) peel slices were dried by application of ultrasonication (U) and carbonation-ultrasonication (CU) as pre-treatments for tray drying (T) at 60 °C. Lesser drying time and higher diffusivity was noticed in CU + T dried samples followed by U + T and T dried samples. Model 'Wang and Singh' was identified as the excellently fitting model to experimental data. SEM images of dried samples revealed the microchannels formation due to U treatment, which were more couloir after CU treatment. Water and oil holding capacity (WHC and OHC) for raw peel powders was higher than ripened peel powders at 40, 60 and 80 °C. WHC and OHC increased significantly after U + T drying or CU + T drying as compared to T drying for ripe and raw peel powder samples. Back extrusion force (BEF) varied from 67.42 to 69.22 N and from 84.6 to 86.02 N for ripe and raw peel samples respectively. Given treatments resulted in lesser colour change and Browning Index. But U + T or CU + T treatment did not affect BEF significantly. CU + T was deemed to be the appropriate drying technique for ripe and raw banana peel drying.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05535-9.

Effect of ultrasonic far-infrared synergistic drying on the characteristics and qualities of wolfberry (Lycium barbarum L.)

This study investigated the effects of ultrasonic frequency, ultrasonic power, irradiation height and temperature on the drying characteristics, quality and microstructure of wolfberry by ultrasonic-assisted far-infrared drying. By fitting five commonly used thin-layer drying mathematical models, it was found that the coefficient of determination (R²) of the Weibull model was 0.99400-0.99825, the root mean square error (RMSE) was 1.2162 × 10^-4-4.5209 × 10^-4, and the reduced chi-square (χ²) was 0.00207-0.00663, which was the best fit. Under the application of ultrasound, the average drying rate of wolfberry increased. Compared with natural drying, the polysaccharide content increased by 33.2 % at 250 mm irradiation height, and the total phenol content increased by 44.9 % at 40 kHz ultrasonic frequency. The antioxidant activity was the strongest, and the total flavonoids content was the highest (2.594 mg/g) at 24 W ultrasonic power. By comparing the microstructure of wolfberry under different drying methods, such as a fresh sample, natural drying, hot air drying, and ultrasonic-assisted drying, we found that the ultrasonic assistance increased the number of micropores on the surface of wolfberry, reduced the damage to epidermal cells, reduced the mass transfer resistance of the drying process and accelerated the drying process. This study shows that ultrasonic-assisted far-infrared drying technology played a significant role in the heat and mass transfer of wolfberry drying, and had great potential in the commercial processing of wolfberry.

Drying behaviour and optimization of drying conditions of pineapple puree and slices using refractance window drying technology

Refractance window drying technology can be used to produce high quality dried fruit products due to its excellent retention of heat sensitive nutrients, organoleptic properties and bioactive compounds. This study optimised conditions for drying of pineapple slices and puree using RWDT. i-optimal design in Design Expert software was used to generate temperature-thickness combinations in form of runs. The independent factors considered included drying temperature (70-90 °C) and thickness (2-3 mm), and the responses included drying time and vitamin C concentration. The optimum solutions generated for RW drying temperature and pulp thickness were 86.2 °C and 2.9 mm for puree and 78.9 °C and 2 mm for slices. The drying times for puree and slices were 58 and 96 min, respectively with corresponding vitamin C content of 64.88 and 46.83 mg/100 g. Drying kinetics of puree and slices were determined at optimal conditions. Drying was found to follow Modified Midilli et al. Model. Pineapple powder obtained using optimal RWD conditions had low water activity (0.41), high solubility (74.64%) and dehydration ratio (4.12). Pineapple reconstituted drinks were developed and evaluated for consumer preference. Acceptability was highest at 15% inclusion of pineapple powder.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13197-021-05302-2.

Experimental investigation and statistical validation of mathematical models for hot air drying traits of carrot

The purpose of this investigation is to analyze the influence of sample shapes or geometry and dryer temperature on drying kinetics of carrot. Three different geometrical shapes including rectangular slab, circular discs and cubical samples, at temperatures of 70 °C, 80 °C and 90 °C, respectively, are dehydrated through hot air convection drying and regression analysis is executed to adjust the outcomes to 4 thin layer drying models. The models were validated by parameters- R² (0.957-0.999), RMSE (0.0066-0.093), AIC (-209 to -54.6 for Henderson and Pabis model, -74.8 to -11.8 for Wang and Singh model, -91.47 to -22.7 for Newton model and -140 to -46.6 for Page model), BIC (-206 to -54 for Henderson and Pabis model, -72.4 to -10.76 for Wang and Singh model, -90.3 to -20.28 for Newton model and -138 to -43.92 for Page model) and residual errors (-0.03 to 0.03). The statistical analysis indicated that Henderson and Pabis model is best suited for the drying purpose. Fick's second law of diffusion is applied to compute values of effective moisture diffusivity, which was maximum for circular disc samples in all the cases and rose with an increase in dryer temperature. It varied in the range of 3.02 × 10^-8 m²/s to 1.86 × 10^-6 m²/s whereas the values of activation energies varied from 68.512 kj/mol to 74.256 kj/mol. The results obtained from this study reveals the experimentally determined drying properties of carrot in order to infer that circular disc shapes possess the ability to optimize the drying process in industries.

Drying kinetics of two fruits Portuguese cultivars (Bravo de Esmolfe apple and Madeira banana): An experimental study

Air convective dehydration was carried out at a laboratory scale using two fruits of cultivars produced in different regions of Portugal: Bravo de Esmolfe apple, from Beiras province, and Cavendish banana, from Madeira Island. Fresh fruits were dried in a tray drier with a hot airstream at different temperatures (35, 40, 45, and 50 °C) and velocity of 1.6 m s⁻¹. Drying rate curves were obtained using a simple mathematical approach applied to the moisture content curves adjusting linear and polynomial functions. Different drying rate stages were noticed in the experiments made with apples (one constant drying rate period followed by two falling drying rate periods), while in the case of the banana the constant drying rate period was not perceived, being dried entirely during a unique falling drying rate period. As expected, the constant drying rate value obtained at the beginning of the experiments with apples is higher when these were conducted at higher temperatures, changing from 8.103 to 14.474 g m⁻² s⁻¹ when the airstream temperature increases from 35 to 50 °C. The correspondent critical moisture contents in the Bravo de Esmolfe apples, at the instant the constant drying rate period stops and the drying rate starts to fall, slightly decreases from 4.800 to 4.134 kg_water/kg_{dry solid}.

This study explored for the first time the drying behavior of these two important fruits that have been increasingly used in the food industry in Portugal, giving important information for the industrialization of its production.

Thin-layer modelling of sweet potato slices drying under naturally-ventilated warm air by solar-venturi dryer

The drying of agricultural produce is an important food preservation measure. However, high energy requirements for drying, limited access to energy sources, small-medium scale farmers experience high post-harvest losses of their produce. Therefore, there is a need to develop and optimize low-cost food preservation technologies. In this study, eleven mathematical models were used to estimate the drying coefficients following non-linear regression method, in hot-air oven and naturally-ventilated solar-venturi drying to find the best fit of the moisture ration models. Sweet potato tubers were sliced at 3, 5 and 7 mm thickness sizes with and without pre-drying treatments. The prepared sweet potato slices were dried in a hot-air oven dryer at a constant temperature of 70 °C in comparison to the naturally-ventilated solar-venturi dryer with a heated ambient air that varied according to the outside environmental conditions. The drying rate of the samples in a hot-air oven dryer was higher than for those in the naturally-ventilated solar-venturi dryer. The results showed that the drying time was significantly (P < 0.05) affected by the thickness size of sweet potato slices (SPS) and that the drying took place at the falling rate period and a constant drying time. The Midilli et al. model was the best fit for predicting the moisture ratio of SPS dried in hot-air oven dryer and naturally-ventilated solar-venturi dryer based on statistical analysis (R² = 0.982-0.999, χ² = 4.60 × 10^-6-5.56 × 10^-5 and RMSE = 0.011-0.067). The D_eff was 3.32 × 10^-9- 6.31 × 10^-9 m s^-1 for the naturally-ventilated solar-venturi dryer and 1.02 × 10^-8 - 2.19 × 10^-8 m s^-1 for the hot-air oven dryer. According to the results obtained, naturally-ventilated, solar-venturi dryer and lemon juice pre-drying treatment are the suitable application for small-medium scale drying of SPS under Pietermaritzburg conditions.

Convective drying of orange pomace at different temperatures and characterization of the obtained powders

In the present study drying of orange pomace was carried out at 50, 60 and 70 °Cand drying kinetics was evaluated. The characterization of the orange pomace powder dried at the three different temperatures was carried out. Modified page model was found to best fit the data on drying, whereas effective moisture diffusivity ranged from 3.34 × 10^-10 to 1.06 × 10^-9 m²/s and the activation energy obtained was 53.07 kJ/mol. The results from powder characterization showed that the chemical composition, water holding capacity and oil holding capacity were not influenced by temperature. The emulsifying activity, swelling capacity and crystallinity were improved by increasing the temperature of drying. The antioxidant capacity and vitamin C content were observed to decrease with increase in drying temperature. There were no noticeable changes in the functional groups or structure due to temperature.

Ethanol and blanching pretreatments change the moisture transfer and physicochemical properties of apple slices via microstructure and cell-wall polysaccharides nanostructure modification

The impacts of ethanol pretreatment and blanching on moisture transfer, microstructure, and nanostructure of cell-wall polysaccharides of apple slices were studied. The physicochemical properties, namely, color, rehydration, and antioxidant capacity were also evaluated. The results corroborated that the use of ethanol and blanching reduced drying time 45-60% and 21-42% at various drying temperatures (50, 60, 70, and 80 °C), respectively, compared to controls. Ethanol loosened the cell wall structure, thereby reducing the internal resistance of moisture diffusion, and the changes in cell wall structure caused by blanching were mainly due to the β-elimination degradation of pectins. Both samples of ethanol pretreatment and blanching possessed lower browning index and higher antioxidant capacity compared with the untreated ones. Overall, ethanol pretreated products exhibited the shortest drying time, less color change and higher antioxidant capacity. These results provide new insights on possible mechanisms about ethanol pretreatment and blanching to improve drying.

Effect of osmotic pretreatment and drying temperature on drying kinetics, antioxidant activity, and overall quality of taikor (Garcinia pedunculata Roxb.) slices

Taikor (Garcinia pedunculata Roxb.) is an underutilized, however nutritious fruit, typically found in Bangladesh and northeast parts of India. Taikor slices (1 ± 0.25 cm thickness) were pretreated for 10 min in 10% sucrose, 10% fructose, and 2% brine solution. Three different temperatures, such as 45, 50, and 55 °C were used to perform the drying operation at 30% constant relative humidity (RH). The thin-layer dehydration characteristics of taikor slices were analyzed using the Newtonian, Page, and Henderson and Pabi's model. The changes in pH, total acidity, color, β-carotene, vitamin C, B vitamins, antioxidant activity, and microbial load calculation were done to compare the comprehensive quality of untreated and pre-treated dried taikor. After assessing the coefficient of determination (R²) and root mean square error (RMSE) values, the Page model was obtained as the best-suited model. For this model, the R² and RMSE values were found to be approximately 1 and below 0.1094, respectively. Among the pretreatments, sucrose helped retain quality characteristics like ascorbic acid (115.25 ± 0.19 mg/100 g), antioxidant activity (33.25 ± 0.07%) more in the dried samples. The brine pretreated sample had minimum microbial growth. Fructose pretreated taikor samples dried at 45 °C exhibited maximum value of B vitamins (B₁ 0.025 ± 0.002 mg/100 g, B₂ 0.016 ± 0.002 mg/100 g, B₃ 0.011 ± 0.001 mg/100 g), total phenolic content (15.78 ± 0.15 mg GAE/100 g), total flavonoid content (11.11 ± 0.08 mg QE/100 g). Overall, fructose pretreated sample dried at 55 °C was found to be the best method for preserving the maximum physical and chemical quality of dried Garcinia pedunculata.

Enhancement of conductive drying of sewage sludge with mechanical compression: Drying kinetics, and interfacial heat transfer behavior

Improving sludge drying efficiency is of tremendous importance for public health, subsequent treatment, and comprehensive utilization. The interfacial thermal resistance between sludge and hot wall greatly limits the conductive drying performance. This study employed mechanical compression to decrease the interfacial thermal resistance. The drying kinetics and interfacial heat transfer behavior were investigated at mechanical loads of 25 to 200 kPa, temperatures of 120 to 210 °C, and sludge thicknesses of 1.0 to 3.0 mm, and were compared to those in the conventional drying process without mechanical load. The increase of temperature and mechanical load and the decrease of thickness improved drying rates. The drying experienced one warm-up period and two falling rate periods. The breakthrough of interfacial vapor film was responsible for the rapid rise in drying rates initially. At the thickness of 3.0 mm, 210 °C, and 100 kPa, the effective moisture diffusivity was increased by 2.5 times, and the apparent activation energy was reduced by 34% compared to the traditional process in the first falling rate period, implying that mechanical compression facilitated moisture migration and bound water desorption. The effective moisture diffusivity in the first falling rate period was increased by 35% compared to the diffusivity in the second falling rate period because of the pressure-driven flow. The decrease in drying rates was due to the transformation from the pressure-driven flow to vapor diffusion-limited flow in the first falling rate period. Additionally, this study provided essential information on developing a new sludge treatment method and establishing the drying model.

Drying dynamics of meat highlighting areas of relevance to dry-aging of beef

Drying of foods is a processing step, which has a variety of outcomes from improving shelf life and product stability, to reducing weight, or to achieving a targeted product eating quality. Drying is key step in the manufacturing of some dried meat products, such as jerky. It is also a major event that occurs when beef is dry-aged, where beef is exposed to air under defined conditions for an extended aging period. Although the conditions typically used to produce dried meat products are significantly different from those that prevail during dry-aging, both involve a gradual removal of water from muscle. As there is a paucity of research on the kinetics of the dehydration process occurring during dry-aging of beef, this paper comprehensively reviews models used to describe drying kinetics in other beef products, in order to gain insights regarding the key factors that impact water removal from meat. Consideration is given as to how the specific conditions during dry-aging such as air flows used (approximately 2 m/s), high air relative humidity, low temperature, and meat geometry will influence the kinetics of the drying. With regard to modeling, equations derived from Fick's second law of diffusion (e.g., thin-layer models) have been used to describe the drying kinetics of small-sized meat products. However, to apply Fick's law to dry-aging, some different considerations may need to be evaluated such as: tridimensional geometry (i.e., whole muscle); uniform initial moisture content; isotropic diffusion; negligible shrinkage;and a combination of internal and external resistances.

Effects of air-impingement jet drying on drying kinetics and quality retention of tomato slices

The purpose was to explore the drying kinetics, the moisture effective diffusivities, color, total polyphenols, lycopene and antioxidant activities of dried tomato slices by air-impingement jet drying (AIJD). The results showed that high temperature increased the drying rate, and Modified Page model accurately predicted the AIJD characteristics of tomato slices. AIJD is better than hot air drying in shortening drying time, enhancing drying rate and decreasing the loss of total polyphenols, lycopene and antioxidant capacity of tomato slices. Tomato slices dried by AIJD also showed higher lightness and redness. Lycopene content and antioxidant activity of tomato slices dried by AIJD were increased by higher drying temperature. Based on experimental data, AIJD at 80 °C can be used in tomato drying process due to the advantages in drying efficiency and content of bioactive compounds. This study will provide helpful information for the production of high quality of dried tomato products.

Enhancing jackfruit infrared drying by combining ultrasound treatments: Effect on drying characteristics, quality properties and microstructure

This study investigates the enhancing effect of power ultrasound (US, 80 W) on the drying characteristics, quality properties and microstructure of jackfruit slices treated with infrared (IR) treatments of 900 W, 1200 W and 1500 W in the meantime. Results showed that when ultrasound was applied, the drying time was reduced by 31%, 35% and 25% compared to pure IR 900 W, 1200 W and 1500 W, respectively. Meanwhile, D_eff values of dried samples were improved. The application of ultrasound significantly increased vitamin C retention and total phenolic content at IR 900 W. The micrographs indicate that ultrasound provided a more porous microstructure of dried jackfruit slices thus accelerating the drying process. The color characteristics of IR-US samples showed no significant change compared to IR drying slices. This study shows that infrared assisted with ultrasound can be a potential method for industrial production of dried jackfruit slices.

Producing non-traditional flour from watermelon rind pomace: Artificial neural network (ANN) modeling of the drying process

An artificial neural network (ANN) model was developed to simulate the convective drying process of watermelon rind pomace used in the fabrication of non-traditional flour. Also, the drying curves obtained experimentally were fitted with eleven different empirical models to compare both modeling approaches. Lastly, to reduce the required fossil fuel in the convective drying process, two types of solar air heaters (SAH) were presented and experimentally evaluated. The optimization of the ANN by a genetic algorithm (GA) resulted in an optimal number of neurons of nine (9) for the first hidden layer and ten (10) for the second hidden layer. Also, the ANN performed better than the best fitted empirical model. Simulations with the trained ANN showed very promising generalization capabilities. The type II SAH showed the best performance and the highest air temperature it reached was 45 °C. The specific energy consumption (SEC) needed to dry the watermelon rind at this temperature and the CO₂ emissions were 609 kWh.kg^-1 and 318 kg CO₂.kWh^-1, respectively. Using the type II SAH, this energy amount would be saved without CO₂ emissions. To reach higher drying temperatures the combination of the SAH and the electrical convective dryer is possible.

The removal of moisture and antibiotic resistance genes in dairy manure by microwave treatment

To characterize the drying of dairy manure during microwave (MW) heating, and to determine the impacts of microwave radiation on reductions of antibiotic resistance genes (ARGs), this study investigated on understanding the effects of microwave heating on solid streams of flushed dairy manure. A series of experiments were performed to determine the rate of drying, moisture removal percentages, change in solids, and the level of ARGs. Manure was exposed to microwave radiation for 30-300 s at a frequency of 2450 MHz. The results showed moisture removal rate (U) up to 0.63-g water per minute per gram of dairy manure. During MW treatment, volatile solid (VS) content was relatively stable. The MW treatment resulted in reduction of ARGs such as sulII, intI1, and tnpA. The ARG concentrations (sulII, intI1, and tnpA) were reduced by 2 orders of magnitude in less than 1 min of microwave heating. The preliminary results of this study showed that MW treatment can be a viable option for drying of dairy manure and reducing ARGs in manure.

Applications of ultrasound to enhance fluidized bed drying of Ascophyllum Nodosum: Drying kinetics and product quality assessment

In this study, ultrasound either as a pretreatment technique or as an integrated technique was employed to enhance fluidized bed drying of Ascophyllum nodosum, and drying kinetics and dried product quality were assessed. In order to compare technology efficiency and dried product qualities, oven drying and fluidized bed drying (FBD) were employed. The novel drying methods included airborne ultrasound-assisted fluidized bed drying (AUA), ultrasound pre-treatment followed by FBD (USP), and hot water blanching pre-treatment followed byFBD (HWB). Six drying kinetics models were used to describe the drying curves, among which the Page model was the best in fitting USP and AUA. Model by Millidi et al. was employed to describe HWB. Airborne ultrasound in AUA did not reduce energy consumption or drying time, but retained total phenolic content (TPC) as well as colour, and exhibited the highest yield among the novel drying methods. USP and HWB showed lower energy consumption and drying time considerably, but the TPC was the lowest among the studied methods. At the same time, USP dried product exhibited the lowest aw, followed by HWB and then AUA. This studyalso demonstrated that FBD could be a very practical drying method on Irish brown seaweed, and ultrasound-assisted drying methods may have potential developments in Irish brown seaweed drying process.

Dehydration of hawthorn fruit juices using ultrasound-assisted vacuum drying

In this study, ultrasound-assisted vacuum drying (UAVD) was employed as a new approach to improve the efficiency and produce dried hawthorn fruit juice powders with acceptable quality. To achieve these goals, the effects of ultrasound intensity (at four levels of 15.29, 20.38, 22.93 and 24.46 kW/m²) were evaluated. The results showed that UAVD significantly shortened the drying time (P < 0.05), and with the increasing ultrasound intensity, the drying rate increased and the drying time decreased. Based on statistical tests, the Page model was found to fit well to the drying kinetics. After drying, a decline in quality of fresh juices was observed. As compared with vacuum drying individually, UAVD significantly reduced the colour degradation, and increased the retention of the total flavonoids content, five flavonoid compounds contents and antioxidant activity. It was shown that UAVD at the higher ultrasound intensity varied from of 20.38 to 24.46 kW/m² contributed to a better quality in the dried juice powders. Overall, this study demonstrates that UAVD is a promising technique for improving the drying efficiency and quality retention of hawthorn fruit juices.

Effect of air velocity, temperature, and relative humidity on drying kinetics of rubberwood

Kiln drying of rubberwood lumbers is a complex transport phenomenon for realistic modeling and simulation. To decouple this complexity, researchers usually divide their research into two parts. The first one is single-lumber drying kinetics to describe how wood lumber responds to its surface conditions. Then they combine this drying kinetics with a lumped transport model or dispersion model or computational fluid dynamics. The mathematical models are then solved numerically to predict the industrial kiln drying behaviors. This work focuses on the drying kinetics of stacked rubberwood lumbers using hot air at different air velocity (0.5, 1.5, 2.5, 3.5, 4.0 m/s), relative humidity (6-67% relative humidity (RH)) and temperature (60-100 °C). The drying kinetics followed the conventional drying theory. However, the two drying periods, namely constant and falling rate (CRP and FRP), were not distinct. As the air velocity increased, the transition from CRP to FRP is faster. The middle of the transition period (at critical moisture content, CMC) moves closer to the fiber saturation point (FSP). The overall mass transfer coefficients in the falling rate period for stacked rubberwood drying were lower than those predicted by the Ananias correlation. Hence, a modified formula was proposed, representing the overall moisture transfer coefficients as a function of air velocity, temperature, relative humidity, and lumbers thickness for the range of variables under investigation satisfactorily. In general, the drying rate and the overall moisture transfer coefficient increased with increasing air velocity, drying temperature, and decreasing RH. Relative humidity directly affects the driving force of moisture transfer rate because higher RH is associated with higher equilibrium moisture content. A lumped parameter model for kiln drying was also developed. After being integrated with the estimated mass transfer coefficient, the model can predict the moisture profiles in lab-scale kiln drying satisfactory, although the model needs more validation data. These kinetic parameters and correlation for stacked rubberwood drying can be used in more complex models and process optimization in future research.

Effect of blanching pretreatment and microwave-vacuum drying on drying kinetics and physicochemical properties of purple-fleshed sweet potato

In this study, drying kinetics and quality of purple-fleshed sweet potato (PFSP) subjected to microwave-vacuum drying were investigated. The effects of hot water and steam blanching pretreatment on physicochemical characteristics of the dried products were also considered. The samples were dehydrated in a custom-made microwave-vacuum system at different power levels including 450, 600 and 850 W. Hot air drying at 70 °C was also conducted for comparison. The results showed that drying time of PFSP under microwave-vacuum conditions ranged from 6 to 12 min, significantly reduced as compared to that of hot air drying (600 min). The improvement of drying rate was also evidenced by increased effective moisture diffusivity (2.22 × 10^-7-4.05 × 10^-7 m²/s) of the samples. Drying kinetics of PFSP was best fitted by Page and logarithmic model with R² ranging from 0.991 to 0.998, and RMSE from 0.016 to 0.030. PFSP dried under microwave-vacuum condition had lower water absorption index and swelling capacity than hot air drying. Color, antioxidant activity and total phenolic content of dried PFSP were also improved under microwave-vacuum drying. The effects of blanching pretreatment on quality of dried PFSP were more dominant in hot air than microwave-vacuum dried samples.

Cold plasma: An emerging pretreatment technology for the drying of jujube slices

Jujube slices were pretreated by cold plasma for 15, 30, and 60 s on each side, followed by hot air drying at 50, 60, and 70 °C. Scanning electron microscopy investigation indicated that the application of cold plasma significantly changed the surface topography of jujube slice by etching larger cavities, which can facilitate moisture transfer and consequently enhance drying rate and effective diffusivity. Modified Henderson & Pabis model and Two-term model were the two most recommended models for describing the drying kinetics of jujube slices. Cold plasma pretreatment improved the contents of procyanidins, flavonoids, and phenolics by 53.81%, 33.89%, and 13.85% at most, respectively, and thereby enhanced antioxidant capacity by 36.85% at most. Besides, cold plasma pretreatment can reduce the production of 5-hydroxymethylfurfural by 52.19% at most. In summary, cold plasma can be used as a promising pretreatment tool for drying processes of jujube slices.

Mathematical modeling and quality parameters of Salicornia fruticosa dried by convective drying

The effect of convective drying at 50, 60 and 70 °C on the drying kinetics and quality parameters of Salicornia fruticosa was investigated. To estimate the equilibrium moisture content a desorption isotherm was performed using five empirical models: Halsey, Caurie, Henderson, Smith and Oswin. The experimental data was also fitted to different drying kinetic models (Logarithmic, Two-Terms, Midilli-Kucuk and Exponential Two-Terms). A numerical simulation using the Finite Volume Method allowed us to describe the evolution of temperature and moisture content distributions during drying. The Henderson model was found to be the most suitable for predicting the equilibrium moisture content of S. fruticosa, with values of X _we in the drying process of 1.51; 1.54 and 1.36 g water/g d.m for 50, 60 and 70 °C, respectively. A good agreement was found between the numerical and experimental results of temperature and moisture during Salicornia drying. The Midilli-Kucuk model presented the best fitting to the drying curves. The effects of drying on S. fruticosa were significant in two quality parameters. Antioxidant capacity decreased in ca. 45% and lightness (> L*) significantly increased at a drying temperature of 70 °C, compared to the fresh samples. The optimum drying temperature where drying time and nutrients loss was minimum was 70 °C. These results can be used to estimate the best drying conditions for producing dehydrated Salicornia. The use of halophytes as sustainable crops is promising, and the vision of their commercial production must be evaluated and considered, given water scarcity in many areas of the planet.

Parametric optimality of tray dried Musa balbisiana Colla blossom

Musa balbisiana Colla blossom has enriched applications as a key constituent of dried vegetable formulations. With restricted prior art, the article addresses the optimality of tray drying characteristics of the blossom from both statistical design and drying kinetics perspective. The process variables in due course of optimization refer to moisture content, antioxidant activity and vitamin C for variation in drying time and temperature. Model fitness, analysis of variance based analysis and numerical optimization were considered during the statistical design of experiments. Drying kinetics involved fitness studies of alternate models, moisture diffusivity and process variable characteristics. Thereby, the sensitivity of both approaches to obtain optimal parameters associated with tray dried product have been targeted for a comparative assessment.