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.     

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.     

Moisture transport in garlic cloves undergoing microwave-convective drying

A laboratory scale microwave dryer was used to dry the garlic cloves, applying microwave power in the range of 10–40 W, air temperature in the range of 40–70 °C and air velocity in the range of 1.0–2.0 m/s. Heat and mass transfer coefficient during the drying process varied in the range of 35.23–79.54 W/m²C and 4.26–6.34 × 10^?2 m/s. The temperature of the product rose rapidly in the early part of the drying and became almost stable thereafter. The Biot mass transfer number confirmed that moisture diffusion was the limiting factor in microwave drying of garlic. The effective moisture diffusivity, which ranged between 1.29–31.68 × 10^?10 m²/s increased with the increase in microwave power but decreased with increase in air velocity.     

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.     

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.     

Experimental determination of effective moisture diffusivities of whole- and cut-rosehips in convective drying

Average effective moisture diffusivities for both the whole- and cut-rosehips were obtained during convective drying. The effects of process variables such as air temperature, air velocity and air absolute humidity on effective moisture diffusivity were studied. The average effective moisture diffusivity in rosehip ranged between 1.45 × 10^?10 and 10.3 × 10^?10 m²/s for whole-rosehip and between 1.44 × 10^?9 and 5.13 × 10^?9 m²/s for cut-rosehip at the temperatures studied. Activation energies for convective drying were found to be 62 kJ/mol for whole-rosehips and 58 kJ/mol for cut-rosehips.     

Thin Layer Modelling of Recirculatory Convective Air Drying of Curd (Indian Yoghurt)

Dahi is one of the most popular fermented milk products consumed in India with excellent therapeutic properties. The initial moisture content of dahi is approximately 5.7 kg water kg dry solid⁻¹. The shelf life of dahi is limited and hence the long term storage is possible in the form of dahi powder which can further be used as a base for formulation of health drink mix. Dahi was dried in a laboratory scale recirculatory convective air dryer to a final moisture content of 0.04 kg water kg dry solid⁻¹. Drying characteristics of dahi were investigated under varying conditions of dahi thickness (0.003 m, 0.004 m and 0.005 m) and drying air temperatures (45°C, 50°C and 55°C) and velocities (1.5 m s⁻¹, 2.0 m s⁻¹ and 2.5 m s⁻¹). Different drying models were used to simulate the observed drying data. The mathematical models were compared based on R-square and reduced chi-square values. The drying characteristics were satisfactorily described by Page, modified page, logarithmic and Midilli et al. models. The Midilli et al. model followed by modified page model provided the best representation of data. Effective moisture diffusivity computed on the basis of Fick's law varied between 2.52 × 10⁻¹⁰ m² s⁻¹ and 1.3 × 10⁻⁹ m² s⁻¹ under experimental drying air temperatures and sample thicknesses at air velocity 2.5 m s⁻¹. The temperature and thickness dependence of effective moisture diffusivity was expressed by an Arrhenius type of equation. The equation showed best fit for diffusivity data at 2.5 m s⁻¹ and varying temperatures and sample thickness.     

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.     

Spouted bed and microwave-assisted spouted bed drying of parboiled wheat

The effect of spouted bed and microwave-assisted spouted bed drying on drying rates of parboiled wheat was investigated. In addition, the effective moisture diffusivities of parboiled wheat were calculated. The drying experiments were performed using 200 g of parboiled wheat, at three different air temperatures (50, 70, 90 °C) and at two different microwave powers (3.5 W/g (db), 7.5 W/g (db)). Microwave-assisted spouted bed drying at microwave power of 3.5 W/g and 7.5 W/g reduced drying time by at least 60% and 85%, respectively compared to spouted bed drying. The effective diffusivity values were in the range of 1.44 × 10^?10–3.32 × 10^?10 in spouted bed drying while they were between 5.06 × 10^?10 and 11.3 × 10^?10 in microwave-assisted spouted bed drying at different experimental conditions.     

A new physical pretreatment of plum for drying

In this paper a new physical pretreatment of plums, consists of piercing them by a thin needle, is proposed to increase the rate of drying. The effect of physical pretreatment on drying time was compared with chemical pretreatment that consists of dipping of plums in hot NaOH solution (1%). Drying experiments were carried out in a convective laboratory dryer at 85 °C and 0.81 m/s air velocity. It was observed that pierced plums were dried faster than chemically pretreated plums. After 480 min moisture ratio of pierced sample was 0.07 while for the chemical method it was 0.25. The moisture ratio at any time was compared with seven different mathematical models and the best model was determined according to the best agreement. Accordingly, two-term exponential model for moisture ratio is found to be superior to the other proposed models. The effective diffusivity was found to be 5.471 × 10^?9 m²/s for chemically pretreated and 1.016 × 10^?8 m²/s for physically pretreated plums.     

Effect of different drying conditions on the vitamin C (ascorbic acid) content of Hayward kiwifruits (Actinidia deliciosa Planch)

In this study, drying kinetics of kiwifruit are investigated experimentally and theoretically under varying drying conditions. Experiments are conducted using air temperatures at 35, 45, 55 and 65 °C, mean velocities at 0.3, 0.6 and 0.9 m s^?1 and, relative humidity values at 40%, 55%, 70% and 85%. Initially, sorption isotherms of the dried kiwifruit slices are determined for different temperatures and equilibrium relative humidity values. The values of the moisture diffusivity, D_eff are obtained from the Fick's diffusion model. The effects of the governing drying parameters on the vitamin C content as well as on the total drying time are determined. The experimental moisture data were fitted to some models available in the literature, mainly the Henderson and Pabis model, the Lewis model and the two-term exponential model and, a good agreement was observed. In addition, it is disclosed that increasing drying air temperature causes more loss in vitamin C in the dried fruits while degradation of vitamin C is reduced with increasing relative humidity of drying air.     

Usage of solar-assisted spouted bed drier in drying of pea

The main objective of this study is to evaluate the effects of solar-assisted spouted bed and open sun drying on the drying rate and quality parameters of pea. Color, shrinkage, bulk and apparent densities, internal and bulk porosities, rehydration capacity and microstructure were the quality parameters investigated in dried product.Drying rate for solar-assisted spouted bed was about 3.5 times of drying rate for open sun drying. Air temperature changed between 20 °C and 27.4 °C during open sun drying while temperature of air at the inlet of solar-assisted spouted bed dryer varied between 35.3 °C and 65.5 °C during the experiments. Effective diffusivities were found to be 0.64 × 10^?10 and 3.27 × 10^?10 m²/s for open sun and solar-assisted spouted bed drying of pea, respectively. In color analysis, it was observed that a* value increased while b* value decreased for both drying methods. Bulk density and apparent density of peas dried under open sun was higher than that in solar-assisted spouted bed drier. In both drying methods, internal and bulk porosities decreased. Shrinkage was more for open sun dried samples. Rehydration capacity for solar-assisted spouted bed dried sample was higher than the one for open sun dried.     

Effect of Nd-doping on structural,thermal and electrochemical properties of LaFe0.5Cr0.5O3 perovskites

The structural, thermal and electrochemical properties of the perovskite-type compound La_1−xNd_xFe_0.5Cr_0.5O₃ (x=0.10, 0.15, 0.20) are investigated by X-ray diffraction, thermal expansion, thermal diffusion, thermal conductivity and impedance spectroscopy measurements. Rietveld refinement shows that the compounds crystallize with orthorhombic symmetry in the space group Pbnm. The average thermal expansion coefficient decreases as the content of Nd increases. The average coefficient of thermal expansion in the temperature range of 30–850 °C is 10.12×10⁻⁶, 9.48×10⁻⁶ and 7.51×10⁻⁶ °C⁻¹ for samples with x=0.1, 0.15 and 0.2, respectively. Thermogravimetric analyses show small weight gain at high temperatures which correspond to filling up of oxygen vacancies as well as the valence change of the transition metals. The electrical conductivity measured by four-probe method shows that the conductivity increases with the content of Nd; the electrical conductivity at 520 °C is about 4.71×10⁻³, 6.59×10⁻³ and 9.62×10⁻³ S cm⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. The thermal diffusivity of the samples decreases monotonically as temperature increases. At 600 °C, the thermal diffusivity is 0.00425, 0.00455 and 0.00485 cm² s⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. Impedance measurements in symmetrical cell arrangement in air reveal that the polarization resistance decreases from 55 Ω cm⁻² to 22.5 Ω cm⁻² for increasing temperature from 800 °C to 900 °C, respectively.     

Finite element simulation for coffee (Coffea arabica) drying

This paper describes moisture diffusivity, shrinkage, equilibrium moisture content and finite element simulated drying of coffee. The moisture diffusivities in different components of parchment coffee were determined by minimizing the sum of square of deviations between the predicted and the experimental values of moisture contents during thin layer drying under controlled conditions of drying air temperature and relative humidity. The drying of coffee bean and parchment was conducted in thin layers at a temperature of 40, 50 and 60 °C with relative humidity in the range of 14–25%. The mean diffusivity values of coffee bean and parchment are related to the temperatures and are expressed by Arrhenius-type equations. The moisture diffusivities of parchment are lower than those of the coffee bean. The shrinkage of coffee bean derived from experiments is expressed as a function of moisture reduction. GAB model is sufficient for the prediction for sorption isotherm of parchment coffee and the parameters of the GAB model are a function of temperature and it is expressed by Arrhenius-type equations. Sensory evaluation of the coffee dried at 40, 50 and 60 °C shows that the overall acceptance by coffee cupping test and the concentration of caffeine is within the acceptable limit. A two-dimensional finite element model was developed for simulate moisture diffusion during drying process of parchment coffee. The finite element model was programmed in Compaq Visual FORTRAN version 6.5. The model simulates the moisture contents in different components of parchment coffee well and it provides a better understanding of the transport processes in the different components of the parchment coffee.     

Thin layer drying kinetics of Gundelia tournefortii L.

The literature surveyed revealed that the drying kinetics of Gundelia tournefortii has not been investigated. In this study, mathematical modeling of the thin layer drying kinetics of G. tournefortii is investigated for both the microwave and open sun drying conditions. Five different microwave power levels ranging from 90 to 800 W were used for the microwave drying. Solar radiation for the open sun drying varied from 350 to 1100 W/m². Drying took place in the falling rate period. Increasing the microwave power caused a significant decrease in drying time. The experimental moisture loss data were fitted to the 14 thin layer drying models. Among the models proposed, the Midilli model precisely represented the microwave drying behavior of G. tournefortii with the coefficient of determination higher than 0.996 and mean square of deviation (χ²), root mean square error (RMSE) and mean bias error (MBE) lower than 1.82 × 10^?4, 12 × 10^?3 and 1.4 × 10^?4, respectively for all the microwave drying conditions studied. Values of drying constant (k) were in the range of 0.0098–0.2943 min^?1 and the effective moisture diffusivities (D_eff) of G. tournefortii ranged from 5.5 × 10^?8 to 3.5 × 10^?7 m²/s. The values of k and D_eff increased with the increase of microwave power level. The logarithmic model was found to best describe the open sun drying kinetics of G. tournefortii. The effective diffusivity of G. tournefortii under the sun drying condition was determined as 2.48 × 10^?10 m²/s.     

A new carbon molecular sieve for propylene/propane separations

A new carbon molecular sieve (CMS) with a propylene/propane separation factor of approximately 27 was synthesized by a facile pyrolysis process from a gel-type strong acid cation exchange resin. The micropore shrinkage process during pyrolysis was investigated using a new high throughput adsorption technique with 48 parallel cells. This significantly reduced the characterization time. The ratio of propylene/propane adsorption rate in the CMS adsorbent changes from 1 to more than 150 when the final pyrolysis temperature changes from 550 to 1000 °C. The best performing CMS pyrolyzed at 850 °C was further characterized using a gravimetric adsorption method. The propylene and propane diffusivities are 1.0 × 10⁻⁹ and 1.1 × 10⁻¹¹ cm² s⁻¹ at 100 kPa and 90 °C. The high propylene/propane diffusivity ratio of 90 is similar to that in zeolite 4A, while the propylene diffusivity was more than 30 times higher than that in zeolite 4A. An effluent of 90 mol% propylene was obtained from a feed of 25 mol% propylene during adsorption/desorption tests using the CMS adsorbent pyrolyzed at 850 °C in a fixed-bed configuration. The new CMS adsorbent is a promising candidate for industrial scale propylene/propane separations.     

Quality evaluation of pineapple fruit during drying process

Pineapple (Anana comosus) slices were dried by hot-air convective drying technique at fixed temperature (45, 60 and 75 °C) and constant air velocity of 1.5 m/s. The effect of drying conditions (drying time and air temperature) on the pineapple quality was evaluated. The quality of dehydrated pineapple was analyzed by color and texture changes, l-ascorbic acid loss and the ability of water uptake during rehydration procedure. Water uptake during rehydration was described by Page model. Statistical analysis of data revealed not significant difference (p > 0.05) among color and mechanical characteristics of pineapple samples dried at different drying temperatures to preset moisture content. Pineapple samples dried at 45 °C had better rehydration ability and more l-ascorbic acid retention than those obtained by air drying 75 °C. Hence, 45 °C drying temperature was best condition for pineapple quality preservation.     

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.     

Photoacoustic thermal characterization of electrical porcelains: effect of alumina additions on thermal diffusivity and elastic constants

The open-photoacoustic-cell technique to measure thermal diffusivity is described in detail. We have applied it to the measurement of thermal diffusivity of porcelain samples with four different alumina additions in the range 0–15 wt% and fired at four temperatures in the range 1270–1350°C. Thermal diffusivity is shown to vary from 4·1×10⁻⁷ m² s⁻¹ for a classical triaxial porcelain to 6·4×10⁻⁷ m² s⁻¹ for 15 wt% alumina addition made mainly at the expense of quartz when the firing temperature was 1325°C. The values of thermal diffusivity are found to be well correlated with the values of the shear and Young's modulus. Good correlation was also observed among the measured values for thermal diffusivity and those for density and mullite to quartz ratio. We conclude that the open-photoacoustic-cell technique has enough sensitivity to detect small changes in composition and microstructure of materials as complex as porcelains.     

The influence of drying air temperature on the physical properties of dried and rehydrated eggplant

Drying processes generally cause volume and surface change of foodstuffs. Information on the porous structure and the mechanical properties of dried food products is needed for determining food quality, process design and estimating properties such as density and moisture diffusivity.In this work we investigated the structural changes induced in eggplant by convective air drying at four different temperatures (40, 50, 60 and 70 °C) and their effect on the subsequent rehydration process. Drying and rehydration kinetic curves were also measured.The changes in physical properties, such as porosity, pore-size distribution and bulk density were determined by Hg porosimetry, scanning electron microscopy and optical microscopy while their effect on the textural characteristics by dynamometric measurements.As expected, the increase of the drying air temperature causes shorter drying times. The drying temperature influences strongly the microstructure of dried samples: the porosity increases with the air temperature, but the structure is better preserved at intermediate temperature (60 °C) as confirmed by the lower firmness values with respect to the other dehydrated samples (40, 50 and 70 °C). In these latter, the longer drying time and the higher temperature, respectively, causes the development of a wrinkled structure. In particular, at 70 °C the structure of dehydrated samples appears totally broken with a consequent faster water uptake during rehydration.