EFFECT OF TEMPERATURE AND RELATIVE HUMIDITY ON THE DRYING RATES AND DRYING TIMES OF GREEN BELL PEPPERS (CAPSICUM ANNUUM L)

Green bell pepper dices were dehydrated at different dry bulb air temperatures (55°, 60°, 65°, 70° and 75°C) and relative humidities (15, 20, 25, 30, 35 and 40%). The effects of temperature and relative humidity (RH) on the drying rates and drying period of diced green bell peppers were determined. Drying rate curves were characterized by a short induction (heating) phase followed by a falling rate period. Near constant rate drying was observed only at 55°C at 15% RH and at 65°C (15% RH). Drying rates generally increased with increasing temperatures and decreasing RH. The effect of temperature on the drying rates became less pronounced with increasing RH Drying rate maxima at 70°C and RH of 15, 20 25 and 40% exceeded those at 75°C, possibly due to case-hardening.     

COMBINED MICROWAVE AND SPOUTED BED DRYING OF DICED APPLES: EFFECT OF DRYING CONDITIONS ON DRYING KINETICS AND PRODUCT TEMPERATURE

ABSTRACT

The influence of microwave power (0 to 8.0 W/g, dry basis) and hot air temperature (25°C to 95 °C) on drying rate and product temperature of diced apples (from 31 % to 5% moisture content, dry basis) in a laboratory microwave and spouted-bed combined dryer was investigated. Product temperature initially increased sharply to a plateau about 12 to 15°C above the spouted bed air temperature at a microwave input power 6.4 W/g. This temperature remained almost constant thereafter. Uniform microwave heating was achieved as evidenced by uniform product color and product temperature. Drying rates increased with increasing spouted-bed air temperature or microwave power level, But higher microwave power caused more darkening of the product. Drying of the diced apples in the microwave and spouted bed drying system exhibited two falling rates periods. The influence of air temperature on effective moisture diffusivity followed an Arrhenius type equation. The activation energies were 23.7 kJ/mol and 26.7 kJ/mol for the first and second falling rate periods, respectively.     

DRYING OF CARROTS IN A FLUIDIZED BED. I. EFFECTS OF DRYING CONDITIONS AND MODELLING

ABSTRACT

Drying curves were determined in a mechanically agitated fluidized bed dryer, at temperatures between 70°C and 160°C, air velocities between 1.1 m/s and 2.2 m/s and stirring rates between 30 rpm and 70 rpm for batch drying of 3 kg lots of carrot slices, measuring the moisture content and shrinking of the particles in time. This was complemented by a study of the rate and degree of swelling of dried carrot particles in water between 20 and 75°C. Drying kinetics were modeled by Fick's second law, for which an optimal agreement with the experimental data was obtained when the effective diffusivity (D _e ) was determined by a correlation based on the air velocity (v), the air temperature (T) and the dimensional moisture content of the carrot particles (X/X _o ). Loss of carotenes is minimized when dehydration is carried out at about 130°C with a drying time below 12 min.     

DRYING CHARACTERISTICS AND PRODUCT QUALITY OF OKRA

ABSTRACT

Effects of size (whole and sliced), pre-treatment (blanching in water and 0.5% NaCl solution at 95° C) and temperature of drying air (40, 55 and 70° C) on the drying characteristics and quality of okra were studied. Estimation of the drying rate established that the drying of okra takes place under the falling rate period. Page's model was found to adequately describe the drying behavior of okra over a wide range of drying conditions used in the study. The coefficients of Page's model were correlated with air temperature and it was found that the dependence of the rate constant on the drying air temperature can be described using the Arrhenius law. The quality of the dried product was found to be best when okra was sliced and blanched at 95° C in 0.5% NaCl solution for 5 min and then dried at 55° C.     

DRYING CHARACTERISTICS OF RED CHILLI

ABSTRACT

Red chilli is widely consumed as a food additive throughout the world. It is blanched/treated to minimize quality loss during processing. This paper reports on various pre-treatments applied before drying and their influence on drying kinetics as well as product quality. Inactivation of peroxidase enzyme was achieved by blanching chillies at 90°C for 3 min in hot water. The physical appearance of the dried product was found to be the best when the blanched samples were soaked in gum acacia solution (0.2% m/v) for 15 min at room temperature. The pre-treated chillies were dried in a tray dryer at selected temperatures (55, 60, 65 and 70°C). Results indicated that drying took place in the falling rate period; the drying kinetics were adequately described by the Page's model. The activation energy for drying was determined to be 41.95 and 41.06 kJ/mol respectively, for blanched and gum-treated chillies. Total pigment content decreased while non-enzymatic browning increased with increase in drying air temperature.     

WATER ADSORPTION AND DRYING CHARACTERISTICS OF OKRA Hibiscus Esculentus L

ABSTRACT

Moisture adsorption characteristics of okra were evaluated at 10, 20, 30° C. Isotherms were found to be of type III. Monolayer moisture contents were evaluated with GAB model. Drying was carried out at 60, 70, 80° C and drying data were analysed to obtain diffusivity values from the period of first felling drying rate. Effective diffusivity increased with increasing temperature. Calculated values of the effective diffusivity showed an Arrhenius type temperature dependence.     

THERMAL ANALYSIS AND DRYING KINETICS OF OLIVE BAGASSE

ABSTRACT

The slow thermal decomposition of olive bagasse at temperatures ranging from 25 to 900° C, with particular stress on the moisture evaporation phenomena, is analyzed making use of thermogravimetry, derivative ihermogravimelry and differential scanning calorimetry. The results obtained demonstrate that Thermal Analysis techniques contribute for the characterization of iniernai moisture transfer processes. “ Drying curves” obtained from Thermal Analysis experiments were compared with thin-layer drying curves of olive bagasse at relatively high temperatures. The existence of a critical moisture content, which distinguishes two types of water liaisons, was demonstrated, and its value quantified at 17-18%.     

OPTIMIZATION OF CONVECTIVE DRYING PROCESS BASED ON ECONOMIC INDICATORS

ABSTRACT

Drying of lightly salted sardine (Sardinella aurita) was accomplished using three air temperatures (35°C, 40°C, 50°C) and three air velocities (0.5 m/s, 1.5 m/s, 2 m/s); the effects of drying conditions on drying kinetics were studied. As for all biological products, air temperature is the main factor influencing the drying kinetics. However, over a given temperature which seems to correspond to protein modification (50°C), and at a high air flow rate (2 m/s and 2.5 m/s) a crust formation on the surface of the fish, due to the combined effect of heat and salt was observed. This phenomenon inhibited the drying rate. From the drying curves, two falling rate periods were observed. The dimensionless drying rate versus a dimensionless moisture content data were regressed by the Marquardt Levenberg non-linear optimization method to obtain an empirical equation describing the salted sardine characteristic drying curve.     

PHYSICAL CHARACTERISTICS AND DRYING RATE OF ECHINACEA ROOT

ABSTRACT

Echinacea angustifolia or the purple coneflower is an important medicinal plant that boosts the immune system. It is believed that the active ingredients are predominantly located in the root. Physical characteristics and drying rates of the root of E. angustifolia from a farm in Saskatchewan, Canada were studied. Root consisted of a main (central) root and secondary root branches. Cleaned roots exhibited wide variations in mass ranging from 15 to 95 g. The central root diameter varied from 9 to 20 mm with an average of 14 mm. The average initial moisture content of the fresh root was 57% (wb). The specific densities of the fresh and completely dried root were 1040 and 1370 kg/m³, respectively; and the corresponding bulk densities of loosely piled roots were 305 and 410 kg/m³. Roots were dried in a convection oven at temperatures of 23, 30, 40, 50, 60 and 70°C. Equations for estimating drying rates, drying constants, and equilibrium moisture content were developed. Increased drying temperatures reduced echinacosides but did not affect alkamides 1 and 2 which are known to be also responsible for medicinal value of E. Angustifolia.     

COFFEE CHERRY DRYING: A TWO-LAYER MODEL

Drying of Coffea arabica cherry was carried out in a thin layer dryer at air temperatures of 40, 50, 60 and 70°C at bed depths of 50, 62.5 and 75mm with air flow rates of 1.5 and 2m³/m²/ min. Since the coffee cherry consis ts of skin and bean, a two layer drying model was developed to characterize the overall drying process for relative humidity range of 46 to 83 per cent. The diffusion coeffcient was determined using drying and equilibrium data and expressed as an Arrhenius- type function. The study revealed that the qualityof the coffee was unaltered over the temperature range studied.     

DRYING OF CARROTS IN A FLUIDIZED BED. I. EFFECTS OF DRYING CONDITIONS AND MODELLING

Drying curves were determined in a mechanically agitated fluidized bed dryer, at temperatures between 70°C and 160°C, air velocities between 1.1 m/s and 2.2 m/s and stirring rates between 30 rpm and 70 rpm for batch drying of 3 kg lots of carrot slices, measuring the moisture content and shrinking of the particles in time. This was complemented by a study of the rate and degree of swelling of dried carrot particles in water between 20 and 75°C. Drying kinetics were modeled by Fick's second law, for which an optimal agreement with the experimental data was obtained when the effective diffusivity (D_e) was determined by a correlation based on the air velocity (v), the air temperature (T) and the dimensional moisture content of the carrot particles (X/X_o). Loss of carotenes is minimized when dehydration is carried out at about 130°C with a drying time below 12 min.     

DETERMINATION OF PARAMETERS AND PRETREATMENT SOLUTION FOR GRAPE DRYING

The drying of Iranian seedless white grapes (sultana) was investigated in a batch operation in a laboratory dryer. The effect of pretreatment and temperature on the drying rate of grapes at constant air velocity were studied. Pretreatment solutions contained different alkaline materials in different concentrations and temperatures. Dipping grapes in an alkaline solution increased the drying rate substantially. Increasing the air temperature in the dryer from 60 to 70°C accelerated the drying rate (for a decrease in drying time) of the pretreated grape. Grapes dried in 450–900 min depending on pretreatment and air temperature. The shorter drying time and best quality dried product were obtained with grapes dipped in a solution of potassium carbonate of 5% at 42°C. The mean apparent diffusivity of moisture for K₂CO₃ pretreatment was calculated at 50, 60, and 70°C, and the values were fitted to an Arrhenius type model. Moisture sorption isotherms of currants were determined at 20, 30, and 40°C using static gravimetric methods. A modified Halsay equation was used to predict experimental data for water activity in a range of 0.1–0.85.     

THERMAL DEWATERING OF DILUTED ORGANIC SUSPENSIONS: PROCESS MECHANISM AND DRYING KINETICS

ABSTRACT

Drying of raw hog manure, a highly diluted suspension of organic and inorganic matter was studied experimentally in the multistage screw-in-trough dryer. Laboratory tests included material characteristics (rheological properties, thermodynamic equilibrium, critical settling point), boiling pattern, and kinetics of convective drying at temperatures from 90 to 120°C and air velocity from 0.5 to 1.5 m/s. Three phases of manure drying were identified, namely boiling and release of volatile compounds, evaporation from viscous liquid, followed by drying of a soft paste, and finish drying of semi-dry granular product. Drying kinetics were quantified in terms of reduced moisture content and a generalized drying curve using the characteristic drying time concept. Field tests were carried out in the pilot multistage screw-in-trough dryer to validate design calculations.

     

COMBINED MICROWAVE AND SPOUTED BED DRYING OF DICED APPLES: EFFECT OF DRYING CONDITIONS ON DRYING KINETICS AND PRODUCT TEMPERATURE

The influence of microwave power (0 to 8.0 W/g, dry basis) and hot air temperature (25°C to 95 °C) on drying rate and product temperature of diced apples (from 31 % to 5% moisture content, dry basis) in a laboratory microwave and spouted-bed combined dryer was investigated. Product temperature initially increased sharply to a plateau about 12 to 15°C above the spouted bed air temperature at a microwave input power 6.4 W/g. This temperature remained almost constant thereafter. Uniform microwave heating was achieved as evidenced by uniform product color and product temperature. Drying rates increased with increasing spouted-bed air temperature or microwave power level, But higher microwave power caused more darkening of the product. Drying of the diced apples in the microwave and spouted bed drying system exhibited two falling rates periods. The influence of air temperature on effective moisture diffusivity followed an Arrhenius type equation. The activation energies were 23.7 kJ/mol and 26.7 kJ/mol for the first and second falling rate periods, respectively.     

HIGH HUMIDITY DRYING OF CORN: EFFECT ON DRYING RATE AND PRODUCT QUALITY

Drying of corn was studied at high and low humidity condiitions. Drying rate was measured, and test weight (bulk density), solid density, stress cracks, and breakage susceptibility of the dried grain at 15% (w.b.) were measured. Twenty four 350-g samples were dried under eight drying conditions in the 71° -104°C temperature range and 0.8%-80% RH relative humidity range. Each sample was exposed to the drying wnditions by using a semi-closed air flow cycle through a thin-layer of grain. High humidity drying reduced the drying rate by up to 44% and did not increase bulk density or solid density significantly as wmpared with low humidity drying. However, high humidity drying did reduce the multiple stress cracks in the corn kernels by up to 33.0 percentage points, increased the number of kernels with no stress cracks by up to 28.7 percentage points, and reduced Wisconsin and Stein breakage susceptibilities by up to 8.9 and 13.5 percentage poinu, respectively.     

PEAR DRYING PROCESS ANALYSIS: DRYING RATES AND EVOLUTION OF WATER AND SUGAR CONCENTRATIONS IN SPACE AND TIME

ABSTRACT

Dried pears are produced in Portugal by a traditional solar drying process and, because they represent unquestionable regional economic interest, some studies are being conducted in order to convert their production to industrial drying methods. In this work the main mass transfer phenomena occurring during drying of pears are investigated. Experiments were carried out to determine the time evolution of the radial profiles of water and sugar content. The drying rates were also studied at constant drying temperatures of 30, 40 and 50°C. The results enable to conclude that the concentration profiles of water and sugar, both in space and time, follow an expected pattern if one takes into account the rates of water removal and the diffusion mechanisms. These also allow to explain why the sugar concentration increases in the periphery of the fruit. The drying rate curves obtained are typical, with the drying process at 30°C being more gradual but also much slower than that at 50°C.     

THE EFFECT OF DRYING AND STORAGE OF SOYBEAN ON THE QUALITY OF BEAN,OIL, AND LECITHIN PRODUCTION

ABSTRACT

A comparative study of soybean drying was carried out between one-stage and two-stage (high–low temperature) drying with shade drying as control. In one-stage drying, the beans were dried at 80, 100, 120, and 140°C, respectively while in two-stage drying, beans were dried at 100, 120, and 140°C in the first stage followed by 80°C in the second stage. The evaluation values after drying showed that high drying temperature caused high skin cracks of the beans. Qualities of extracted crude oil characterized by free fatty acids (FFA), peroxide value (PV), phospholipids (PL) and nonhydratable phospholipids (NHP) were not significantly effected at p<0.05 by different drying methods but NHP had the increasing trend with the drying temperature and two-stage dried beans tended to have NHP higher than one-stage dried beans. The quality of protein in meal determined in terms of protein dispersibility index (PDI) was less than 15% when drying temperature in one-stage drying was higher than 80°C and when the temperature at the first stage of two-stage drying was higher than 100°C. Drying temperature also had the effect on the quality of lecithin when considered in term of the acetone insoluble value (AI). Free fatty acids of extracted crude oil increased when dried beans were stored for two months at 35°C while PL decreased especially in the first month of storage. However, the AI value of lecithin did not change with time.     

KINETICS ON COLOR CHANGES DURING DRYING OF SOME FRUITS AND VEGETABLES

Abstract

The effect of drying conditions on color changes of apple, banana, carrot and potato during conventional and vacuum drying was investigated. The Hunder color scale parameters redness, yellowness and lightness were used to estimate color changes during vacuum and conventional drying at 50, 70 and 90°C. Air humidity during conventional drying was regulated at 15, 30 and 40%. Air temperature and humidity affected redness and yellowness, but not lightness. A first order kinetic model was fitted to experimental data adequately for both redness and yellowness. The rate of color deterioration was found to increase as temperature increased and air humidity decreased, for both drying methods and all the examined materials.     

DRYING KINETICS FOR SOME FRUITS: PREDICTING OF POROSITY AND COLOR DURING DEHYDRATION.

ABSTRACT

Drying kinetics of four fruits (prune, quince, fig and strawberry) were studied by using a simple mass transfer mathematical model involving a characteristic parameter (K) as a function of process variables. The model was tested with data produced in a laboratory air dryer, using non-linear regression analysis. The investigation involved three values of sample thickness (5, 10, 15mm) and three different air temperatures (50, 60, 70?°C).

The parameters of the model were found to be greatly affected by sample thickness and air temperature. The effect of moisture content on the porosity of three fruits (namely avocado, prune and strawberry) was also investigated. A simple mathematical model was used to correlate porosity with moisture content. It was found that porosity increased with decreasing moisture content.

Samples of three fruits (avocado, prune and strawberry) were investigated to estimate color changes during conventional drying at 70?°C. A first order kinetic model was fitted to experimental data with great success. It is found that the color of avocado and strawberry change while the color of prune remains the same.

Furthermore, the water sorption isotherms of three fruits (avocado, prune and strawberry) at 25° temperature were determined experimentally and the parameters at the GAB equation were evaluated by means of non-linear regression analysis. The use of the above equation produced a very good fit.     

Foam Mat Drying of Alphonso Mango Pulp

The foam mat drying of Alphonso mango pulp using various food foaming agents, namely soy protein (0.25, 0.5, 1.0, and 1.5%) with methyl cellulose (0.5%), glycerol mono stearate (0.5, 1.0, 2.0 and 3.0%), and egg albumen (2.5, 5.0, 10 and 15%) with methyl cellulose (0.5%), was studied. Drying was carried out in a batch type thin layer dryer at four drying temperatures (60, 65, 70, and 75°C) on 1-, 2-, or 3-mm thickness foamed samples. The optimum concentrations of each foaming agent were determined to be 1% soy protein, 2% glycerol mono stearate, and 10% egg albumen. All were obtained after 25 min whipping time. The drying time was lower for foamed mango pulps as compared to non-foamed pulp at all drying temperatures. Biochemical analysis showed that the foam mat dried powder at 60°C retained a significantly higher (P < 0.05) content of biochemical compounds than at higher temperatures. The treatment of mango pulp with 10% egg albumen and 0.5% methyl cellulose and drying at 60°C (1-mm foam thickness), retained the highest nutritional quality characteristics than the other treatments.