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

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

Drying kinetics and quality changes during drying of red pepper

A mathematical model is proposed to simulate the process of drying of individual pieces of red pepper under constant external conditions and to predict changes in some nutritional and organoleptic attributes of the product. The model was solved numerically to obtain moisture content and temperature as well as ascorbic acid and carotenoids concentration in the product as a function of time. A good agreement between predictions and experimental data at different drying temperatures was obtained.Water sorption isotherms of red pepper were determined in the range 20-50 °C and represented by two different sorption equations. Drying kinetics were represented by a diffusive model, the effective moisture diffusivity ranging from 5.01 to 8.32×10⁻¹⁰ m²/s with an activation energy of 23.35 kJ/mol. Degradation kinetics for ascorbic acid and total carotenoids were measured in the range 50-70 °C and modelled as first-order reactions. The rate constants increased with temperature and product moisture content. Average activation energies for carotenoids and vitamin C degradation were 50.1 and 26.9 kJ/mol, respectively.     

Drying kinetics of whole durum wheat pasta according to temperature and relative humidity

Drying kinetics of bran-free and bran-rich pasta (whole durum) was determined according to temperature (40, 60 or 80 °C) and relative humidity (65%, 75% or 85%). Compared to temperature, relative humidity in drying chamber had a greater effect on pasta effective moisture diffusivity (α<0.01), and both parameters responded to a modified Arrhenius-type equation. Activation energy of pasta (11.4 kJ mol⁻¹) was lower than reported in the literature. Bran changed the course of pasta drying, depending on temperature and relative humidity. When relative humidity was higher than 75%, effective moisture diffusivity of bran-rich pasta decreased but the reverse was observed below 75%. Above 76 °C, equilibrium moisture content of bran-rich pasta was higher than bran-free pasta. In conclusion, optimal drying conditions for bran-rich pasta were different than standard (bran-free) pasta. Close control of relative humidity in pasta drying unit would be critical, especially under high relative humidity and high temperature conditions.     

Drying characteristics of mango slices using the Refractance Window™ technique

Mango slices (1 and 2 mm thickness) were dried by using the Refractance Window™ (RW) technique with the water bath temperature set at 92 °C. Drying kinetics, water activity, and color change were determined and compared with those obtained by drying the slices in a tray dryer at 62 °C and an air velocity of 0.52 m/s. At 1 h, moisture contents of 0.013 (for 1 mm sample) and 0.048 (for 2 mm sample) kg water/kg dry solid for RW, and 0.966 (for 1 mm sample) and 3.614 (for 2 mm sample) kg water/kg dry solid for tray drying were obtained and water activity was less than 0.5 for RW and close to 0.97 for tray drying. The tray dryer took 4 h to reach results similar to those of RW at 1 h. The samples dried by RW exhibited diffusivities of 4.40 × 10⁻¹⁰ (for 1 mm sample) and 1.56 × 10⁻⁹ (for 2 mm sample) m²/s, which are larger than those exhibited by the air-dried samples, 2.08 × 10⁻¹¹ (for 1 mm sample) and 6.83 × 10⁻¹¹ (for 2 mm sample) m²/s.     

Drying kinetics of semi-finished cassava crackers: A comparative study

Drying kinetics of semi-finished cassava crackers was investigated in this paper using a hot air dryer at seven levels of drying air temperatures in the rage of 50-80 °C, a fixed air flow velocity using a fan speed of 0.18 kW, and a fixed level of thickness at 1.5 mm. A comparative study was performed among mechanistic and empirical models: the diffusion model, Newton model, Page model, Modified Page model, Henderson and Pabis model, MFNN (Multilayer Feedforward Neural Network), and ANFIS (Adaptive-Network-based Fuzzy Inference System), to estimate dynamic drying behaviors of semi-finished cassava crackers. Among these models, MFNN was found to be the most suitable for predicting moisture ratio of the product based on r² (regression coefficient), and MSE (mean squared errors between the experimental data and predicted values).     

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

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

Evolution of porosity, shrinkage and density of pasta fortified with pea protein concentrate during drying

The aim of this work was to study the impact of fortification with commercial pea protein concentrate on the evolution of the moisture content, density, shrinkage and porosity of pasta made from durum wheat semolina during drying. Pasta were processed from durum wheat semolina enriched with pea protein concentrate at 0, 5, 10 and 15 g 100-g-dry matter⁻¹ and dried at low (40 °C) and high (80 °C) temperature. Moisture content, density, shrinkage and porosity and effective moisture diffusivity coefficients were linked through theoretical development. It enabled to study the behaviour of the properties as a function of drying time. The results showed that drying temperature has a greater effect on the studied properties than enrichment with pea protein concentrate. Drying at 80 °C increased radial and total shrinkage compared to drying at 40 °C, but no differences were observed for longitudinal shrinkage. Pasta dried at 80 °C were denser and overall less porous, but had greater internal porosity. The volumetric percentage of water lost during drying replaced by air within the pasta matrix was lower at 80 °C. Scanning electron microscopy analysis showed that the gluten network of pasta dried at 80 °C seems denser and more continuous. Effective moisture diffusivity coefficients of pasta dried at 80 °C were higher at 5 and 10 g 100-g-dry matter⁻¹ enrichment level compared to the control.     

Evaluation of Mathematical Models for Prediction of Thin-Layer Drying of Banana Slices

Drying characteristics of bananas were experimentally determined. The drying experiments were carried out in a hot air dryer at four inlet temperatures of 50, 60, 70 and 80°C, at a constant air velocity of 2.4 m/s and relative humidity of 4–25%. The experimental results were fitted to five thin-layer drying models and it was found that the Page and Logarithmic models gave better fit that the other models. Values of the effective diffusivity ranged from 7.374 × 10^?11 to 2.148 × 10^?10 m²/s. Activation energy for moisture diffusion of the banana slices was found to be 32.65 kJ/mol.     

Modeling Effective Moisture Diffusivity of Wheat (Tajan) During Air Drying

Drying conditions can greatly affect the physical and mechanical properties of grains. The drying process must be controlled to reduce or minimize drying damage. In this paper the thin layer drying behavior of wheat (Tajan) in a convective dryer is experimentally investigated. The mathematical modeling by using thin layer kinetics drying models available in literature was performed. Drying experiments were conducted at inlet drying air temperatures of 35, 45, 50, 60 and 70°C and at a fixed drying air velocity of 0.3 m/s and initial moisture content of 0.26–0.27 (d.b.). The effects of drying air temperature on the model's parameters were predicted by a linear regression analysis. The constants and coefficients of this model were be explained in terms of drying air temperature. A correlation coefficient (r) of 0.99 was found for the multiple regression model of moisture content during the drying process using different temperature values. Values of the diffusion coefficients for the whole kernel ranged from 2.28 × 10^?11 to 1.14 × 10^?10 m²/s.     

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

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

Drying behaviour of hazelnuts

A diffusion-based drying model has been used to model the single-layer drying of whole hazelnuts (hull, air-gap and kernel). The drying of whole hazelnut was simulated by means of the numerical solution of Fick's second law for a composite solid consisting of an air gap which is between two solid bodies. The Crank–Nicholson implicit numerical method has been applied to solve the diffusion equation with variable mass diffusivity for whole hazelnut. The numerical data so obtained has been presented in the form of a series of curves which represent the drying characteristics of a whole hazelnut. Experimental results from whole hazelnuts were correlated with the theoretical results. A correlation describing the diffusivity of the whole hazelnut with moisture content and temperature was established, when the expression of diffusivity for hazelnut was used. Predicting the drying behaviour of the hazelnut for a known value of initial moisture content, equilibrium moisture and equivalent radius, a good agreement was obtaind between the experimental data and prediction. Whole hazelnut diffusivity was determined at 25–45°C, air velocity 0·2–0·3 ms⁻¹, 60% relative humidity of air, using the theoretical curves that best fit the data. The diffusivity of whole hazelnut was determined as a function of drying air temperature and velocity. © 1998 SCI.     

Simulation of drying behaviour of a small spherical foodstuff in a microwave assisted fluidized bed of inert particles

Drying behaviour of a small spherical porous particle was investigated in a microwave assisted fluidized bed of inert energy carriers. A pilot-scale microwave assisted fluidized bed dryer with inert particles was set up for this purpose. Glass beads particles were used as inert materials. Based on the simultaneous heat and mass transfer, a mathematical model was proposed for predicting the temperature variation and moisture distribution in the drying sample during drying. A numerical solution was developed for the proposed model using an implicit finite difference method in one dimensional system. The model was validated with experimental average moisture contents of green peas during drying and the effects of microwave power density, drying air velocity and also drying air temperature were discussed.     

Effect of chemical and physical pretreatments on the convective drying of cape gooseberry fruits (Physalis peruviana)

Drying of cape gooseberry fruits is a slow process because of the low permeability to moisture of the fruit’s waxy skin. In this work, the effect of chemical pretreatments (sunflower oil/K₂CO₃ or olive oil/K₂CO₃ at 28 °C, and NaOH/olive oil at 96 °C) and physical pretreatments (blanching) to break down the waxy surface and accelerate moisture diffusion during drying, was assessed. Drying was carried out at 60 °C and 2 m/s air velocity for 10 h. The lowest moisture content (0.27 kg water/kg db), the highest vitamin C content (0.36 mg/g), and the greatest rehydration capacity (1.89) were obtained in fruits pretreated with olive oil (9.48%) and K₂CO₃ (4.74%). However, the greatest changes in color (ΔE^* = 15.05) and chroma (ΔC^* = 9.03) were also associated to fruits pretreated with olive oil and K₂CO₃. The effective diffusivity of water during drying was 7.37 × 10⁻¹¹ m²/s in pretreated samples compared with 6.61×10⁻¹¹ m²/s for untreated samples.     

Microwave, air and combined microwave-air-drying parameters of pumpkin slices

Pumpkin slices (Cucurbita maxima) which weighs 50 g with moisture of 9.31 g water/g dry solids, were dried using three drying methods, microwave, air and combined microwave-air. Drying continued until slice moisture reduced to 0.1 g water/g dry solids. Two different microwave output powers 160 and 350 W were used in the microwave drying. Drying treatments in air-drying were 50 and 75 °C and 1 m/s fan speed. The combination drying in which microwave and air-drying were applied together was four different combination levels. Drying periods lasted 125-195, 45-90 and 31-51 min for microwave, air and combined microwave-air-drying, respectively, depending on the drying level. Energy consumption was 0.23-0.34, 0.61-0.78 and 0.29-0.42 kW h, respectively. In this study, measured values were compared with predicted values obtained from Page's semi-empirical equation. Optimum drying period, colour and energy consumption was obtained when microwave and air-drying was applied simultaneously and the optimum combination level was 350 W microwave applications at 50 °C.     

Moisture diffusivity of rough rice under infrared radiation drying

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

Drying kinetics of the individual layer of cocoa beans during heat pump drying

Investigation was carried out to study the drying kinetics of the individual layer of cocoa beans, namely the testa and cotyledon, during heat pump drying. The cocoa beans were dried in thin layer using dehumidified air at 28.2 °C, 40.4 °C and 56 °C. Moisture contents of the bean, testa and cotyledon were recorded during drying. Reduction in moisture content was relatively fast at the testa as compared to the cotyledon in the initial two hours of drying. Subsequent drying showed a crossover region where the moisture content of the testa was higher than the cotyledon. The final moisture content of the testa was found to be higher than the inner cotyledon at the end of drying. This showed that moisture migrated from the cotyledon (lower moisture content) to the testa (higher moisture content) during drying. Although such transfer mechanism seems contradict but this can be further explained by the mass transfer potential concept as postulated by Luikov where the transfer of moisture is due to moisture potential difference instead of moisture content difference. Product quality analyses showed percent retention of cocoa polyphenols ranged from 44% to 73% as compared to freeze dried sample. Bean hardness was found reasonably comparable to the commercial sample and increased with decreasing moisture content.     

Effect of different drying temperatures on the moisture and phytochemical constituents of edible Irish brown seaweed

The effect of different temperatures on the drying kinetics and the phytochemical constituents of edible Irish brown seaweed, Himanthalia elongata were studied. This kinetic study involved the modelling of the terms of Fick’s diffusion equation, for estimation of the diffusion coefficients. The diffusivity coefficient increased from 5.6 × 10⁻⁰⁷ to 12.2 × 10⁻⁰⁷ m²/s as the drying temperatures increased with an estimated activation energy of 37.2 kJ/mol. The experimental data was also fitted to different empirical kinetic models, Newton, Logarithmic and Henderson-Pabis, and the goodness of fit for the different models was evaluated. The effect of drying temperatures on the phytochemical constituents in seaweed was also evaluated. Drying at 25 °C resulted in 49% and 51% reduction in the total phenol and total flavonoid content, respectively, as compared to fresh seaweed. However, the reduction declined as the drying temperatures were increased. The scavenging effect on DPPH radical was also greater for the fresh seaweed as compared to the dried form. An increase in the phytochemical content was seen for higher temperatures (35 °C and 40 °C) when the moisture content reduced by 50% indicating that this semi-dry state is even more nutritious than the fresh form and could be an interesting starting point for seaweed processing.     

Thermal properties and resistant starch content of green banana flour (Musa cavendishii) produced at different drying conditions

The objective of this research was to verify the effect of drying conditions on thermal properties and resistant starch content of green banana flour (Musa cavendishii). The green banana flour is a complex-carbohydrates source, mainly of resistant starch, and quantifying its gelatinization is important to understand how it affects food processing and the functional properties of the flour. The green banana flour was obtained by drying unripe peeled bananas (first stage of ripening) in a dryer tunnel at 52 °C, 55 °C and 58 °C and air velocity at 0.6 m s⁻¹, 1.0 m s⁻¹ and 1.4 m s⁻¹. The results obtained from differential scanning calorimetry (DSC) curves show a single endothermic transition and a flow of maximum heating at peak temperatures from (67.95 ± 0.31) °C to (68.63 ± 0.28) °C. ANOVA shows that only drying temperature influenced significantly (P < 0.05) the gelatinization peak temperature (Tp). Gelatinization enthalpy (ΔH) varied from 9.04 J g⁻¹ to 11.63 J g⁻¹ and no significant difference was observed for either temperature or air velocity. The resistant starch content of the flour produced varied from (40.9 ± 0.4) g/100 g to (58.5 ± 5.4) g/100 g, on dry basis (d. b.), and was influenced by the combination of drying conditions: flour produced at 55 °C/1.4 m s⁻¹ and 55 °C/1.0 m s⁻¹ presented higher content of resistant starch.     

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

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

Low-temperature,low-relative humidity drying of rough rice

The use of low air temperatures (26–34 °C) and relative humidities (19–68%) to dry thin-layer samples of rough rice to the desired 12.5% moisture content was investigated. Drying rates and durations and their effects on the quality parameters of head-rice yield, color, and pasting viscosity of long- and medium-grain rice cultivars harvested at 19.6% and 17.5% moisture contents, respectively, were determined. Results showed that dehumidification of the drying air had greater potential for increasing drying rates at 26 °C than at 30 and 34 °C. Low drying air temperatures and relative humidities had no adverse effects on head-rice yield or color compared to controls. Peak and final viscosities of low-temperature and low-relative humidity dried samples were similar to controls.