Direct and indirect power ultrasound assisted pre-osmotic treatments in convective drying of guava slices

Application of ultrasound to osmotic dehydration of guava slices via indirect sonication using an ultrasonic bath system and direct sonication using an ultrasonic probe system was studied. Pre-treatments were designed in three osmotic solution concentrations of 0, 35, and 70 °Brix at indirect ultrasonic bath power from 0 to 2.5 kW for immersion times ranging for 20–60 min and direct ultrasonic probe amplitudes from 0 to 35% for immersion times of 6–20 min. The calculated ultrasound intensities from calorimetric ultrasound power dissipated indicated that direct sonication was more intensive than indirect sonication. The general linear model (GLM) showed that ultrasound input (power and amplitude), osmotic solution concentrations, and immersion time increased the water loss, solid gain, and total colour change of guava slices significantly with P < 0.0005. Indirect sonication in osmotic solutions contributed to high water loss and solid gain with acceptable total colour change than direct sonication. Applying ultrasound pre-osmotic treatment in 70 °Brix prior to hot-air drying reduced the drying time by 33%, increased the effective diffusivity by 35%, and decreased the total colour change by 38%. A remarkable decrease of hardness to 4.2 N obtained was also comparable to the fresh guava at 4.8 N.     

Correction of moisture and sucrose effective diffusivities for shrinkage during osmotic dehydration of apple in sucrose solution

Shrinkage, moisture and sucrose effective diffusivities were correlated for infinite slab shape samples of apple during osmotic dehydration in sucrose solution. Experiments were carried out in the sucrose solutions of different concentrations (30%, 40% and 50%) and temperatures (30 °C, 40 °C and 50 °C). The two parameter model, developed by Azuara et al. (1992), was used to predict water loss and solid gain at equilibrium condition. Moisture and sucrose diffusivities were estimated by fitting the experimental moisture loss and solid gain data to the modified form of Fick's second law of diffusion, considering the shrinkage of the apples during osmotic dehydration. Results showed that the volume of the samples decreased linearly with water loss (WL) and weight reduction (WR). For above conditions of osmotic dehydration, effective diffusivities without considering the shrinkage were found to be in the range of 1.36 × 10⁻¹⁰ m²/s–2.00 × 10⁻¹⁰ m²/s, and those with considering the shrinkage were in the range of 0.87 × 10⁻¹⁰ m²/s–1.27 × 10⁻¹⁰ m²/s. The values of the effective diffusivities estimated by considering the shrinkage were smaller than those without considering this phenomenon.     

Mass transfer modeling of equilibrium and dynamic periods during osmotic dehydration of radish in NaCl solutions

Equilibrium and dynamic mass transfer properties of water and solute were investigated during osmotic dehydration (OD) of radish slices in sodium chloride (NaCl) solutions. OD experiments were performed in 0.05, 0.15 and 0.25 g/g solutions at different temperatures (25, 40, 55 and 70 °C) using a brine-to-vegetable mass ratio of 15:1. An analytical solution for unsteady-state mass transfer based on Fick's second law of diffusion was used to mathematically describe water loss and solute gain curves and for the simultaneous estimation of diffusion coefficients and final dehydration–impregnation levels in product. Under such experimental conditions, effective water diffusivity was in the range of 1.85–2.74 × 10^?9 m²/s, whereas solute diffusivity values were between 0.74 × 10^?9 and 2.88 × 10^?9 m²/s. Corresponding dehydration and impregnation levels of radish at equilibrium were estimated between 0.25 and 0.81 g water/g fresh product and 0.01–0.11 g solute/g fresh product, respectively. As demonstrated, current results may be applied to determine the set of conditions (process time, brine concentration and process temperature) yielding an osmodehydrated radish product within given specifications.     

Quality optimisation of combined osmotic dehydration and microwave assisted air drying of pineapple using constant power emission

Combination of osmotic dehydration with microwave assisted air drying offers increased flexibility for process control and product quality. Osmotic dehydration (55°Brix solution at 40 °C for 90 min) combined with microwave assisted air drying (MWAD) was tested on smooth cayenne pineapples. The influence of the four most relevant processing parameters (osmotic treatment time, microwave power, air temperature and air velocity) was studied using a 2⁴ circumscribed central composite experimental design. The product quality was evaluated in terms of charred appearance at the surface, moisture content, soluble solids content, water activity, firmness, colour and volume. Microwave power and air temperature were the two most important processing parameters that influenced the quality of the dehydrated pineapple, with the parameters most affected by the operating conditions being water content and percentage of charred pieces. Only in the latter was a significant quadratic effect found, all others were approximately linear. There was also a significant interactive effect between microwave power and air temperature affecting the percentage of charred pieces. Model predictions using a quadratic surface for water content and % charred pieces were validated with an additional experiment. Quadratic models were used to indicate optimum drying conditions for various targets.     

Optical and mechanical properties of cocona chips as affected by the drying process

The effect of the application of a pre-osmotic treatment to obtain hot air dried cocona (Solanum sessiliofurum Dunal) chips was studied. The drying kinetics and the optical and mechanical properties of cocona chips obtained by the combined method of osmotic dehydration and hot air drying (OD + HAD) and by only hot air drying (HAD) were compared. Samples were dried by hot air at 60 °C. For the combined method, they were pre-dried to a moisture content of 75 g_water/100 g, immersed in a 55 °Brix sucrose solution at 25 °C for 48 min. The pre-osmodehydration applied did not influence the subsequent hot air drying kinetics, resulting in a final product with 0.055 ± 0.005 g_water/g_cocona. The optical properties of OD + HAD chips were more favorable, exhibiting a smaller color change with respect to the fresh fruit (±15 units) than the HAD samples (±23 units). On the other hand, the OD + HAD chips presented more fracture peaks than HAD ones, this related with a structure with a higher degree of crispness, a very desirable property for a chip product.     

Air-Drying Kinetics of Osmotically Dehydrated Fruits

ABSTRACT

The air drying kinetics of fresh and osmotically dehydrated fruits (apples) was determined. Two sugars, glucose and sucrose, were used as osmotic dehydration agents. Three levels of sugar concentration (15%, 30% and 45%) and several times of immersion into the sugar solution were used. Following the osmotic preconcentration, the fruit samples were dried at 55°C and the weight of material was recorded. The effective water diffusivity of samples treated under various osmotic conditions was estimated and the results were related to the sugar content and the bulk porosity of the samples. The effective water diffusivity, resulting from the application of the diffusion equation to the drying kinetics of the apples was found to decrease significantly for the samples pretreated by a concentrated sugar solution (e.g. 45%), evidently due to the lower porosity and other physicochemical factors. The low diffusivity may be beneficial in the storage stability and utilization of dehydrated fruits.     

Characterisation of industrial tomato by-products from infrared drying process

The thin-layer infrared drying behaviour of industrial tomato residues, peels and seeds, was experimentally investigated in the temperature range from 100 °C to 160 °C. The drying rate was found to increase with temperature, hence reducing the total drying time. In particular, as drying temperature was raised from 100 °C up to 160 °C, the time period needed to reduce the moisture content of the sample from 236.70 wt% down to 5.26 wt% (dry basis) was observed to decrease from 99.5 min to 35 min.Using a non-linear regression (Marquart's method) together with a multiple regression analysis, a mathematical model for the thin-layer infrared drying process of industrial tomato residues was proposed. The effective moisture diffusivity is dependent on moisture content; the average values for the diffusivity coefficients at each temperature were obtained using Fick's second law of diffusion, and varied from 5.179 × 10^?9 m²/s to 1.429 × 10^?8 m²/s over the temperature range. The temperature dependence of the effective diffusivity coefficient was described following an Arrhenius-type relationship. Activation energy for the moisture diffusion was determined as 22.23 kJ/mol.     

OSMOTIC DEHYDRATION KINETICS OF BLUEBERRIES

Abstract

The kinetics of moisture loss and solids gain during osmotic dehydration of blueberries under different conditions of temperature (37°C - 60°C), concentration of the sucrose solution (47°Brix - 70°Brix) and contact time between fruit and sucrose solution (0.5 h - 5.5 h) were studied, and modeled based on Fick's law of unsteady state diffusion. The study showed that all factors influenced moisture loss and solids gain (p<0.001), both generally increasing with temperature (T) and sucrose concentration (C). Based on the diffusion model, the calculated effective moisture diffusivity (D_m) ranged from 1.98 × 10^?10 to 5.10 × 10^?10 m²/s and the effective solids diffusivity (D_s) ranged from 2.54 × 10^?11 to 2.22 × 10^?10 m²/s. Both D_m and D_s showed increasing trends with temperature and sucrose concentration, and could be modeled as quadratic functions of T and C.     

Experimental modelling of infrared drying of industrial grape by-products

The thin-layer infrared drying behaviour of industrial grape by-products was experimentally investigated in the temperature range from 100 to 160 °C. The drying rate was found to increase with temperature, thus reducing the total drying time. In particular, as drying temperature was raised from 100 °C up to 160 °C, the time period needed to reduce the moisture content of the sample from 204.32% down to 38.89% by weight (dry basis) decreased from 60.5 to 21 min.Using a non-linear regression (Marquart's method) together with a multiple regression analysis, a mathematical model for the thin-layer infrared drying process of wet grape residues was proposed. The values for the diffusivity coefficients at each temperature were obtained using Fick's second law of diffusion. They varied from 11.013 × 10^?9 to 26.050 × 10^?9 m²/s along the temperature range. The temperature dependence of the effective diffusivity coefficient was expressed by an Arrhenius type relationship. Activation energy for the moisture diffusion was determined as 19.27 kJ/mol.     

Study of the Drying Kinetics of Green Bell Pepper and Chemical Characterization

The present work aimed, on one hand, the study of the drying of green peppers, in terms of drying kinetics evaluated at 30°C, 40°C, 50°C, 60°C and 70°C, having the experimental data been fitted to different empirical kinetic models from literature. This kinetic study was then complemented with the modelling in terms of Fick's diffusion equation.On the other hand, the chemical characterization in fresh and after drying at the lowest and highest temperatures was analysed, for evaluation of the effect of drying and drying temperature on the chemical composition of the product. In this way, the analyses made were: moisture content, sugar content, proteins, ash, fat, fibre and acidity.From the results obtained, it was concluded that the empirical models that best describe the dehydration kinetics were the Page and Newton models. From the experimental data was possible to estimate the diffusivities, which range between 9.0 × 10⁻¹⁰ at 30°C and 8.0 × 10⁻⁹ m² s⁻¹ at 70°C.Moreover, it was verified that drying influences the chemical composition of the peppers, but, conversely, the influence of the drying temperature was not very significant.     

MASS TRANSFER IN BANANA CHIPS DURING OSMOTIC DEHYDRATION

ABSTRACT

The effects of temperature ( 50, 60 and 70 °C ), sucrose concentration ( 50, 60 and 70° Brix ) and pH ( 6,7 and 8 ) on the mass transfer during osmotic dehydration of banana chips were studied. Fitting a diffusion model gave apparent diffusivity values varied from 2.77 to 2.66 × 10^?9 m² s^?1 and depending on temperature and sucrose concentration but not on pH changes. The effct of syrup/product volume ratio on the mass transfer kinetics was also investigated.     

Convective drying of onion: Kinetics and nutritional evaluation

The present work aimed, on one hand, to study of the drying of onions in terms of drying kinetics, which was evaluated at 30 °C, 50 °C and 60 °C. The experimental data was fitted to different empirical kinetic models from the literature, and this kinetic study was then complemented with the modelling if terms of Fick's diffusion equation, for estimation of the diffusion coefficients. On the other hand, the chemical characterization in fresh and dried onions at different temperatures (varying from 30 °C to 70 °C) was analysed, to evaluate the effect of drying and drying temperature on the chemical composition of the product. In this way, the analyses of moisture content, sugar content, crude protein, ash, fat, crude fibre, acidity and vitamin C were made and reported in this paper.From the results obtained it was verified that some chemical components of the onions are not affected by drying (ash, fat, protein and fibre) whereas some others are considerably influenced by drying (sugars, acidity and vitamin C). The present work allowed concluding that the three empirical models tested (Newton, Modified Page and Logarithmic) all describe relatively well the dehydration kinetics at the three temperatures analysed. Moreover, from the experimental data it was possible to estimate the diffusivities, which range between 3.33 × 10^?09 m²/s at 30 °C and 8.55 × 10^?09 m²/s at 60 °C.     

Convective drying characteristics of sludge from treatment plants in tomato processing industries

The present work is mainly focused on the study of the thin layer drying behaviour of sludge from water treatment plants in tomato processing industries, using a convective dryer. The drying experiments were conducted at inlet temperatures of drying air of 30 °C, 40 °C and 50 °C and at an airflow rate of 0.9 m/s and 1.3 m/s. The drying rate was found to increase with temperature and velocity, hence reducing the total drying time. In particular, as drying temperature was raised from 30 °C up to 50 °C, the time period needed to reduce the moisture content of the sample from 173 wt% down to 7 wt% (dry basis) was observed to decrease from more than 760 min to 470 min (0.9 m/s) and from 715 min to 295 min (1.3 m/s).Using a non-linear regression (Marquart's method) together with a multiple regression analysis, a mathematical model for the thin-layer convective drying process of sludge from treatment plants in tomato processing industries was proposed. The values of the diffusivity coefficients at each temperature were obtained using Fick's second law of diffusion, and varied from 6.11 × 10^?10 m²/s to 2.54 × 10^?9 m²/s over the temperature and velocity range. The temperature dependence of the effective diffusivity coefficient was described following an Arrhenius-type relationship. The activation energy for the moisture diffusion was determined as 30.15 kJ/mol and 36.70 kJ/mol, for airflow rates of 0.9 m/s and 1.3 m/s respectively. Air temperature 40 °C and drying airflow rate 1.3 m/s were found adequate to reduce drying energy consumption as well as to optimise the dryer loading/unloading periods.     

Effect of high pressure on mass transfer kinetics of granny smith apple

The mass transfer kinetics during osmotic dehydration of granny smith apple slices in 60 Brix fructose and sucrose solution was studied at atmospheric pressure and at elevated pressure of 200–600?MPa at 40°C. The moisture and solute fractions in apple slices during osmotic dehydration under high pressure were predicted by Weibull frequency distribution model. The calculated effective moisture diffusivity values of apple slices suspended in fructose and sucrose solution during high-pressure treatment (0.1–600?MPa) were in the range of 6.35?×?10^?10 to 3.60?×?10^?9?m²/s and 7.96?×?10^?10 to 4.32?×?10^?9?m²/s, respectively.     

Convective air drying characteristics of sweet potato cube (Ipomoea batatas L.)

The effects of drying conditions on the drying behavior of sweet potato (Ipomoea batatas L.) were investigated in a cabinet dryer. The convective air drying was carried out under five air temperatures; 50, 60, 70, 80 and 90 °C, five air velocities of 1.5, 2.5, 3.5, 4.5 and 5.5 m/s and three sweet potato cubes of 5, 8 and 12 mm thickness. Data were analyzed to obtain diffusivity values from the period of falling drying rate. Results indicated that drying took place in the falling rate period. Moisture transfer from sweet potato cubes was described by applying the Fick's diffusion model, and effective moisture diffusion coefficients were calculated. Effective diffusivity increased with increasing temperature. An Arrhenius relation with an activation energy value of 11.38 kJ/mol expressed effect of temperature on the diffusivity. Two mathematical models available in the literature were fitted to the experimental data. The page model gave better prediction than the first order kinetics of Henderson and Pabis model and satisfactorily described drying characteristics of sweet potato cubes.     

Effects of Pretreatments of Sliced Vegetables with Trehalose on Drying Characteristics and Quality of Dried Products

Effects of pretreatments with trehalose on drying of sliced vegetables (potato and carrot) were experimentally investigated. Two different pretreatment methods were tested. Sliced vegetables were steam-blanched and then immersed in a sugar solution. In another method sliced vegetables were coated with sugar powder, and then steam-blanched. Solid gain and water loss during pretreatment were measured. The isothermal drying experiments were carried out at 303, 313 and 323 K. Sorption isotherms of dried samples were determined by a standard gravimetric method at 303, 313 and 323 K. Pretreatments reduced the water content of vegetable samples due to osmotic dehydration. Less shrinkage, better colour properties and better cell reconstruction properties were observed for samples pretreated with trehalose either with solution or with powder.     

Effect of osmosis and ultrasound pretreatment on the moisture adsorption isotherms of quince

The effect of pretreatment osmotic–ultrasonic dehydration on the sorption isotherms of quince was determined by static gravimetric method at temperatures of 30 °C, 45 °C, and 60 °C. The curves obtained can be considered as type II according to the Brunauer–Emmett–Teller (BET) classification. Adsorption data were fitted into seven isotherm models. The best fit of the experimental data was obtained with Peleg for both fresh- and pretreated dried quince slices.Thermodynamic properties such as net isosteric heat, differential entropy, enthalpy–entropy compensation, and spreading pressure were determined from moisture adsorption isotherm data of quince. The net isosteric heat of sorption and differential entropy decreased with increasing moisture contents in an exponential function. A plot of differential heat versus entropy satisfied the enthalpy–entropy compensation theory. The spreading pressure increased with increasing water activity, and decreased with increasing temperature. The value of net isosteric heat, differential entropy and spreading pressure of untreated samples is higher than that of pretreated samples of quince.     

Enthalpy of formation and dehydration of lithium and sodium zeolite beta

Zeolite Li-BEA and Na-BEA with Si/Al = 3–4 were synthesized by alumination and ion exchange, then characterized by XRD, TG–DSC and NMR. The enthalpies of formation and dehydration of Li and Na ion exchanged zeolite beta are investigated by high temperature oxide melt solution calorimetry. For Li-BEA, the formation enthalpies of formation from oxides at 25 °C are 25.6 ± 1.7 kJ/mol TO₂ for the dehydrated zeolite and −8.45 ± 0.94 kJ/mol TO₂ for the fully hydrated zeolite; for Na-BEA they are −2.4 ± 0.6 kJ/mol TO₂ for the dehydrated and −17.8 ± 1.0 kJ/mol TO₂ for the fully hydrated zeolite. The integral dehydration enthalpy at 25 °C is 33.2 ± 1.8 kJ/mol H₂O for Li-BEA and 16.5 ± 1.1 kJ/mol H₂O for Na-BEA. The partial molar dehydration enthalpies of both Li-BEA and Na-BEA are a linear function of water content. Molecular mechanics simulations explore the cation and water molecule positions in the framework at several water contents.     

Osmotic Dehydration of Apple Cylinders: II. Continuous Medium Flow Heating Conditions

Mass transfer of apple cylinders during osmotic dehydration was quantitatively investigated under continuous medium flow conditions. The influences of the main process variables (solution concentration, operation temperature, contact time, and solution flow rate) were determined. A second-order polynomial regression model was used to relate weight reduction (WR), moisture loss (ML), solids gain (SG), and mass diffusivity (D _m and D _s ) to process variables. The conventional diffusion model using a solution of Fick's unsteady state law involving a finite cylinder was applied for moisture diffusivity and solute diffusivity determination. Diffusion coefficients were in the range of 10^?9–10^?10 m²/s, and moisture diffusivity increased with temperature and flow rate, increased with solution concentration (> 50°Brix), and decreased with increasing solution concentration (< 50°Brix), but solids diffusivity increased with temperature and concentration and decreased with increasing flow rate. A continuous-flow osmotic dehydration (CFOD) contactor was developed to be a more efficient process in terms of osmotic dehydration efficiency: time to reach certain weight reduction (T _w ) and moisture loss (T _m ) were shorter than that of conventional osmotic (COD) dehydration processes. Effectiveness evaluation functions used in this study could be widely applied to osmotic dehydration system evaluation.     

The effect of silica doping on neodymium diffusion in yttrium aluminum garnet ceramics: implications for sintering mechanisms

The Nd³⁺ cation diffusion into transparent polycrystalline YAG (Y₃Al₅O₁₂) was investigated as a function of temperature and silica content. Thin neodymium oxide layers were deposited on sintered YAG substrates prior to annealing under air at temperatures from 1400 to 1600 °C. Bulk and grain boundary neodymium diffusion coefficients were measured by secondary ion mass spectrometry. The experimental results show that silica addition increases the diffusivity of Nd³⁺ by a factor 10 whatever the diffusion path, probably as a result of extrinsic point defects formation, especially rare-earth vacancies.The experimental diffusion data were used to elucidate the sintering mechanism of Nd:YAG ceramics in the temperature range 1450–1550 °C. Firstly, it appeared that the intermediate stage of solid-state sintering should be controlled by the rare-earth diffusion along the grain boundary with an activation energy of about 600 kJ mol^?1. Secondly, grain growth mechanism at the final stage of liquid-phase sintering was investigated for silica-doped Nd:YAG samples. Thus, the grain growth should be limited by the reaction at interfaces at a temperature lower than 1500 °C, with an activation energy of about 880 kJ mol^?1. At higher temperature, it seems to be limited by the ionic diffusion through the intergranular liquid phase, with an activation energy of 250 kJ mol^?1.