Air Drying Characteristics Research Articles

Effects of Different Pretreatments on Hot Air Drying Characteristics, Nutrition, and Antioxidant Capacity of Tartary Buckwheat Sprouts.

In order to enhance the quality of hot air drying for Tartary buckwheat sprouts and minimize the loss of active substances, this research explored the impact of Color Protection(CP), Osmosis(OM), Blanching (BC), β-cyclodextrin (β-CD), and Ultrasound (US) in conjunction with hot air drying on the color, nutritional value, antioxidant properties, and other attributes of Tartary buckwheat sprouts. The findings revealed that as the drying temperature increased from 50 °C to 70 °C, the drying duration for Tartary buckwheat sprouts decreased across all treatment groups, leading to a higher dehydration rate. Treatments involving CP, US, and BC effectively reduced the drying time of Tartary buckwheat sprouts. Sprouts subjected to CP, β-CD, and US treatments exhibited elevated L* values and decreased a* values and displayed a more vibrant green color. When exposed to a hot air setting of 60 °C, the total flavonoid content in the CP, OM, β-CD, and US groups increased by 8.76%, 6.76%, 12.34%, and 4.25%, respectively, compared to the Control Group (CK). The application of the CP, OM, β-CD, and US treatments enhanced the sprouts' ability to combat ABTS and DPPH free radicals. Notably, under hot air conditions of 60 °C, the β-CD treatment demonstrated the most effective quality preservation during the hot air drying process for sprouts. This study provides valuable insights into the drying behavior of Tartary buckwheat sprouts and offers guidance for optimizing the drying procedures in industrial settings. Tartary buckwheat sprouts contain a variety of polyphenols and have a high water content. The study of changes in active components such as polyphenols and their alteration mechanisms in Tartary buckwheat sprouts under different processing methods is particularly important for the development of sprout processing.

Transformation of cell wall pectin profile during postharvest ripening process alters drying behavior and regulates the sugar content of dried plums

This study evaluated the effects of postharvest ripening (0–6 days, D0–6) on cell wall pectin profile, infrared-assisted hot air-drying characteristics, and sugar content. Results showed that during postharvest ripening progress, the content of water-soluble pectin (WSP) and chelate-soluble pectin (CSP) increased while the content of Na2CO3-soluble pectin (NSP) and hemicellulose (HC) decreased. In addition, the average molecular weight of WSP increased while the average molecular weight of NSP decreased. Secondly, the drying time of plums with different postharvest ripening periods was in the order: D3 < D4 < D2 < D1 < D0 < D5 < D6. Furthermore, the sugar content of dried plums was mainly influenced by drying time, with three stages of sugar changes observed, tied to moisture content: (1) Sucrose hydrolyzes (50–85%); (2) Fructose and glucose degrade (15–50%); (3) Sorbitol degrades (15–42%). These findings indicate that the transformation of cell wall pectin profile during the postharvest ripening process alters drying behavior and regulates the sugar content of dried plums. Chemical compounds studied in this articleGalacturonic acid (PubChem CID: 439215); Acetone (PubChem CID: 180); Distilled water (PubChem CID: 962); Trans-1,2-Diaminocyclohexane-N, N, N, N′-tetraacetic acid (PubChem CID: 2723845); Na2CO3 (PubChem CID: 10340); Glucose (PubChem CID: 5793); fructose (PubChem CID: 2723872) sucrose (PubChem CID: 5988) sorbitol (PubChem CID: 5780) and Sodium borohydride (PubChem CID: 4311764).

Air-drying characteristics of fresh and pretreated (African Oil Bean) &lt;I&gt;Pentaclethra macrophylla benth.&lt;/i&gt; cotyledons

Processing of African Oil Bean Cotyledons (AOBC), a valuable source of protein has been a bottleneck because of the associated drudgery. In addition, the shelf life of the processed bean is very short; the cotyledon turns green shortly during storage due to putrefaction. On the basis of the above, there is a need to produce shelf-stable cotyledons which could be rehydrated when needed. Three portions were separately soaked in each solution of sodium chloride (3 %), sodium meta-bisulfite (300 ppm), ascorbic acid (300 ppm) for 1h, and one portion were subjected to natural fermentation for three days, while the other was used as control. All the samples (single and double cotyledons) were oven-dried at 50, 60, 70, and 80o C to constant weight. The dehydration rate of AOBC decreased gradually until the water activity of the oil bean cotyledon reduced to less than one. Moisture diffusivity increased from 4.9061×10-10 – 2.091 × 10-9 m2/s, and varied with drying temperature, thickness, and pretreatments. Midilli and Kucuk model (R2 = 0.9702 - 0.9940) showed a better fit than other drying models. Effective moisture diffusivity is direct of the samples is reliant on air-drying temperature and can be described by the Arrhenius equation. The activation energy of drying of the African Oil Bean cotyledon was in the range of 10.29 – 27.12 kJ/mol. Finally, the addition of preservatives proved to be highly effective on the drying rate and the other studied parameters as well as the shelf stability of the AOBC.

Impact of different thin layer drying temperatures on the drying time and quality of butterfly pea flowers

With attractive flower colours ranging from dark green to purple, Butterfly pea (Clitoria ternatea L.) is grown year-round in Vietnam. The purpose of this study is to determine the effect of air temperature on drying time and antioxidant compounds of Butterfly pea flowers, fitting the drying curves and testing the goodness of fit. In this study, air drying characteristics of the Butterfly pea flowers were determined using drying air temperature from 55oC to 70oC at a constant air velocity of 1 m/s. The data of experimental moisture loss were fitted to selected seven thin-layer drying models. The effect of drying conditions on the anthocyanin and total phenolic compound changes of Butterfly pea flower were compared. The effect of temperature on the diffusivity was described using the Arrhenius equation with an activation energy of 71.63 kJ.mol- ¹. At increasing temperature, the effective moisture diffusivity values ranged from 2.39×10-12 and 7.76×10-12 m²s - ¹. The mathematical models were compared according to the three statistical parameters such as the coefficient of determination (R2 ), reduced chi-square (χ 2 ) and root mean square error (RMSE) between the observed and predicted moisture ratios. The highest value of R2 (99.8%) and the lowest values of χ 2 (0.0004) and RMSE (0.0178) were observed for drying air temperature of 70oC. Among the seven mathematical models tested with experimental data, the Page model could sufficiently be described the drying characteristics of the Butterfly pea flower.

Ultrases Ön İşleminin Elma Dilimlerinin Kurutma ve Rehidrasyon Karakteristikleri ile Mikroyapısına Etkisinin Araştırılması

In this study, the effects of ultrasound pretreatment on hot air drying and rehydration characteristics and microstructure changes of apple slices were examined. Slices of apple cv. Granny Smith having 5 mm thickness were used as the material. Pretreatments with ultrasound application were done by an ultrasonic generator with 20 kHz frequency. Effect of pretreatment time (10, 20, 30 min) and amplitude (55 and 100 %) were evaluated. Drying experiments were performed in a cabinet drier at 60°C with 0.3 m.s-1 constant air velocity. Application of ultrasound pretreatment decreased the drying time of apple slices in some conditions. Amongst the five thin layer drying models tested, the Page and Modified Page models found to be the best fitting models for the expression of the drying of apple slices. Microstructural changes caused by ultrasound pretreatment enhanced the rehydration ability of dried apples. As the pretreatment time and ultrasound amplitude increased, the rehydration ratio had an increasing trend. Peleg model represented the rehydration kinetics of the samples successfully. Changes in the microstructure of the apple samples caused by the ultrasound pretreatment were clearly observed with scanning electron microscopy images. Structural changes, caused by ultrasound pretreatment in apple tissues, resulted in low shrinkage values.

Experimental study of wet porous sand layer air-drying characteristics

An experimental study has been carried out to investigate the convective air-drying characteristics of a wet sand layer. The experimental setup allows dynamic measurements of both sand layer weight and temperature, with hot air flowing towards the sand layer surface to ensure a uniform drying of it. Experiments are conducted for a 4 mm thick sand layer for three air temperatures of 45, 60 and 75 °C. The lumped parameter method is used to analyze the sand layer heat transfer. The results show that the sand layer temperature continuously increases throughout the drying process, which can be divided into three stages, i.e. the initial rapid, intermediate slow, and final rapid increase stages. There is no constant temperature stage that is often observed in water film evaporation experiment. The drying process can also be divided into three stages according to the sand layer drying rate variation, they are the increasing, constant, and decreasing rate stages, which roughly correspond to the three temperature rise stages. The lumped parameter analysis result supports that the convective heat from the hot air is used mainly for the water evaporation.

Investigation of the effect of temperature on Tunisian clay product during drying process

The aim of this work was to evaluate the influence of drying temperature on the convective drying process of clay sample as well as on the effective diffusivity. The study was performed on Tunisian raw-clay product in here simple spherical geometry with initial moisture content of 0.35 kg water/kg d.b. Air-drying characteristics were investigated in a laboratory convective dryer for a temperature range varying from 30 to 60 °C at a constant air velocity of 1,44 m/s with an air humidity ratio of 50%. Four analytical solutions based on Fick’s and Crank’s diffusion equations were proposed to describe the drying process. The first and the second equations neglected shrinkage effect while the two other equations consider it as a fundamental parameter. According to the obtained results, it was proved that the increase in air temperature increases the drying rate, as well as the effective diffusion coefficients. Based on the analytical solutions used in this study, it was concluded that the model including the shrinkage effect gives the lowest value of the effective diffusion coefficient.

Experimental investigations and analysis of wet porous sand layer air-drying process

Experimental studies have been conducted to investigate the wet porous material convective air-drying characteristics. An experimental setup is designed and constructed to examine the air-drying process of a wet sand layer, and it allows dynamic measurements of both the sand layer weight and temperature. Hot air flows down towards the sand layer upper surface to realize a uniform drying of it and multiple thermocouples are embedded in the sand layer to evaluate its temperature distribution. Experiments are carried out for three sand layer thicknesses of 2, 4 and 8 mm and for three hot air temperatures of 45, 60 and 75 °C. Water film evaporation experiments are also performed to obtain the convective heat and mass transfer coefficients, which are then used for the lumped parameter analysis of the sand layer heat and mass transfer. The results show that in the water film evaporation experiment, the water temperature initially increases and then remains constant at the air wet-bulb temperature for a long period of time until the water all evaporates. In the sand layer drying experiment, however, the sand layer temperature continues to increase throughout the drying process, which can be divided into three stages, i.e. the initial rapid, intermediate slow, and final rapid increase stages. The lumped parameter method is employed to analyze the sand layer heat transfer because of the small sand layer thickness. Such analysis uses the heat transfer coefficient obtained in the water film evaporation experiment and the sand layer temperature increasing rate to calculate the sand layer moisture content and drying rate. The obtained results agree well with the experimental data. The evolution of water film cover fraction on the sand layer upper surface during drying is also discussed by assuming that the water evaporation occurs mainly at the sand layer upper surface at the drying stage at which the sand layer upper surface is fully wet or partly wet.

Air-Drying Characteristics of Yellow Bell Pepper

Air-Drying Characteristics of Yellow Bell Pepper

Selection of convective moisture transfer driving potential and its impacts upon porous plate air-drying characteristics

A theoretical model is developed to simulate the convective air-drying process of an unsaturated porous plate using the representative elementary volume (REV) approach. The model considers a variety of transport mechanisms and uses the specific humidity (mass fraction) as the convective mass transfer driving potential, which is thought to suit for modeling of non-isothermal water evaporation into air fluid. The partial differential equations included in the model are discretized and solved fully implicitly using the predicator-corrector method. Calculations are performed with two water vapor concentrations including the specific humidity and vapor density as the mass transfer driving potential to clarify how the potential selection will affect the drying characteristics. Calculations are performed for plate thickness of 15mm and air temperatures of 320.15, 333.15 and 348.15K. The results show that use of the vapor density as the driving potential causes underestimations of the wet surface temperature and plate moisture content, and this tendency becomes more conspicuous for a lower air temperature. It is recommended to use the specific humidity as the mass transfer driving potential to better describe the moisture and heat transfer during the convective drying of an unsaturated porous medium.

Convective Air Drying Characteristics and Qualities of Non-fried Instant Noodles

Abstract Convective air drying characteristics and qualities of non-fried instant noodles at five temperatures from 80 to 120°C and velocities of 1.0, 2.0 and 3.0 m/s were investigated. Different mathematical models were fitted to study the drying behaviors and the Logarithmic model was the most adequate in describing the drying tests. Results showed that the drying process occurred in a falling rate periods and the effective moisture diffusivity increased with temperature and velocity, ranging from 4.41×10−8 to 1.75×10−7 m2/s with an activation energy of 16.73 kJ/mol. The rehydration attributes changed with both velocity and temperature. Increasing temperature and velocity decreased hardness, increased cohesiveness and resilience generally while had no impact on springiness. Drying temperature greatly influenced the color of noodles, whereas velocity displayed no significant effect. Microstructural analysis indicated that noodle presented hollow and porous structure with numerous and small voids, which might partly explain their distinct behaviors.

Hot Air Drying Characteristics of Sukkari Date (Phoenix dactylifera L.) and Effects of Drying Condition on Fruit Color and Texture

Abstract Convective hot air drying was used to dry date fruits at different air temperatures and velocities. The kinetics of drying was evaluated by 10 common models. The fruit color and texture were examined before and after drying. Drying time increased as both drying temperature and air velocity decreased. Best fits to the experimental data were provided by the Midilli and Kucuk model, followed by the logarithmic, two-term exponential, and Henderson–Pabis models. Drying affected the fruit color and texture. To minimize such changes, the range of drying temperature and air velocity should be 60–70°C and 2 m/s, respectively.

Convective Air Drying Characteristics for Thin Layer Carrots

Introduction: Carrot is one of the most commonly used vegetables for human nutrition due to high vitamin and fibre content. Drying is one of the oldest methods of food preservation, and it represents a very important aspect of food processing. Sun drying is the most common method used to preserve agricultural products in most tropical countries; this technique is extremely weather dependent, and has the problems of contamination with dust, soil, sand particles and insects. Also, the required drying time can be quite long. Therefore, using solar and hot-air dryers, which are far more rapid, providing uniformity and hygiene are inevitable for industrial food drying processes. Aim: This paper presents a kinetic study of convective drying without pre-treatment of carrot. The effects of the temperature of the drying agent, the speed of the drying agent and the thickness of the kinetics of drying the sample of carrots were investigated. Materials and methods: The experiments were carried out with the aid of an installation for drying food products, that is capable of ensuring the temperature of the drying agent (air) in the range of +25 ... +125 °C. The drying process was conducted at temperature of 45 °C in first hour of process, 2 hours at 55 °C, and 3 hours at 60 °C. The air velocity was setup at 1.0 - 2.5 m/s. Carrots were divided into segments of a thickness of 0.4 cm. Two mathematical models available in the literature were fitted to the experimental data. Results: The drying rate increases with temperature and decreases with the sample diameter. The Page model is given better prediction than the Henderson and Pabis model and satisfactorily described drying characteristics of carrot slices. Conclusions: The most important characteristics of carrot required for simulation and optimization of the drying were studied. The values of calculated effective diffusivity for drying at 45, 55 and 60oC of air temperature and 1.0, 1.5, 2.0 and 2.5 m/s of air flow velocity. The effective diffusivity increases as air-flow rate and temperature increases. Page’s empirical model showed a good fit curves than the Henderson and Pabis model.

Hot Air Drying and Vacuum Drying Characteristics of Scarlet Runner Beans

Abstract The drying characteristics and volume changes of scarlet runner beans were measured under various conditions to obtain useful basic information for the optimum drying method and conditions. The sample was dried using two drying methods: hot air drying and vacuum drying. The measured changes in moisture content of the sample with the hot air drying process were in good agreement with the exact solution of the infinite plane sheet model. The estimated diffusion coefficients were 3.8×10 -7 -7.4×10 -7 (m 2 h -1) for hot air drying and were related to absolute temperature by an Arrhenius-type equation. The hull of the scarlet runner bean is hard and thick, and the drying rate of the sample was much slower than that of other beans. To establish an efficient drying method without the quality loss, the vacuum drying characteristics of the sample were measured at several levels for temperature and initial moisture content. For the vacuum drying process, an exponential model could be used to estimate the changes in moisture content of the sample. The values of diffusion coefficient for vacuum drying were approximately twice as much as the values of diffusion coefficient for hot air drying at the same temperature. The effects of drying method, temperature, and initial moisture content on the sample quality were investigated, and the optimum drying method and conditions for scarlet runner beans were proposed. Volumetric changes in the sample were determined by measuring particle density. The specific volume of the sample was represented as a linear function of moisture content.

Evaluation of Air Drying Characteristics of Sliced Ginger (Zingiber officinale) in a Forced Convective Cabinet Dryer and Thermal Conductivity Measurement

A forced convective cabinet dryer is used to study the hot air drying characteristics of sliced ginger placed in a single layer. Ginger is dried from initial moisture content of 87-88% (w.b.) to the final moisture content of 6-7% (w.b.). Experiments are carried out with four different drying air temperatures of 45, 50, 55 and 60°C by keeping the air velocity fixed at 1.3 m/s. The moisture removal rate is found to increase with increase in temperature and drying process occurred at falling rate period for all the temperatures studied. A non-linear regression analysis is conducted to investigate the accuracy of prediction of ten selected thin layer drying models. From the statistical analysis, a best fit curve is obtained which gives better agreement to the experimental drying data. Further, the thermal conductivity of ginger is determined experimentally and a mathematical expression of thermal conductivity as a function of moisture content has been established, which can predict the experimental data within 1.5% accuracy.

Intermittent and Continuous Microwave-Convective Air-Drying Characteristics of Sage (Salvia officinalis) Leaves

The effect of microwave-convective air-drying (continuous and intermittent) and convective air-drying of sage (Salvia officinalis) on color and essential oil content were studied. For microwave-convective air-drying, four pulse ratio levels (PR1, PR2, PR3, and PR4) at 25 °C drying air temperature were used and the average drying rates were 0.404, 0.158, 0.114, and 0.085 kg H2O kg−1 DM min−1 for PR1, PR2, PR3, and PR4, respectively. For convective air-drying, two drying temperatures of 40 and 50 °C were examined and the average drying rates were 0.005 and 0.006 kg H2O kg−1 DM min−1 for 40 and 50 °C, respectively. The experimental data were fitted to 11 different moisture ratio models to describe the drying kinetics under various drying conditions. Page model was found satisfactory to describe the drying curves of sage leaves. Comparing with the fresh sage, lightness (L*), greenness, and yellowness decreased for all drying applications. Lightness, greenness, and yellowness of the convective air-dried sage leaves were higher than those of microwave-convective air-dried sage leaves. The deviation from fresh product color (ΔE*) increased as the pulse ratio or the drying air temperature increased. The total quantity of essential oils of sage decreased considerably during microwave-convective air-drying whereas the loss of essential oils was limited during air-drying.

Effect of osmotic pretreatment on air drying characteristics and colour of pepper (Capsicum spp) cultivars

Air-drying characteristics of fresh and osmotically pretreated (40°B, 50°B and 60°B sucrose solutions for 9h) four pepper cultivars namely, Rodo (Capsicum annuum), Shombo (Capsicum frutescens), Bawa (Capsicum frutenscens) and Tatashe (Capsicum annuum), and CIE L*a*b* parameters of air-dried (50, 60, 70 and 80°C) peppers were investigated. Moisture diffusivity and activation energy (Ea) were calculated from Fick's law and analogous Arrhenius equation, respectively. Colour difference, chroma and hue angle of fresh- and osmo-oven dried peppers were evaluated. Drying rates occurred predominantly in the falling rate. Moisture diffusivity varied from 8.071 × 10(-10)-1.048 × 10(-8), 7.710 × 10(-11)-1.018 × 10(-9), 9.807 × 10(-9)-1.746 × 10(-8) and 8.748 × 10(-10)-1.464 × 10(-9)m(2)/s for Bawa, Rodo, Shombo, and Tatashe, respectively. Ea for moisture diffusion during drying of peppers varied from 53.86 to 84.86kJ/mol and was affected by cultivars and osmotic pretreatment concentration. Osmotic pretreatment and drying temperature had significant effect (p < 0.05) on a*, b*, chroma and hue angle values of dried peppers.

Effect of Osmotic Dehydration on Air-Drying Characteristics of Chayote

In this study the effect of osmotic dehydration (OD) on the air-drying kinetics of chayote (Sechium edule (Jacq.) Swartz) fruits was investigated. Fresh and osmotically dehydrated chayote parallelepipeds (1 × 1 × 2 and 4 × 4 × 2 cm) were subjected to convective drying at air temperatures of 50 and 60°C, with air velocities of 1.5 and 2.5 m/s. The OD pretreatments were performed in 10 and 25% NaCl solutions (w/w) at 25°C during 3 h using a solution-to-fruit mass ratio of 4:1. The use of higher air velocities notably accelerated drying rates as manifested through significantly higher drying rate constants estimated with Page's model, whereas no effect of temperature was observed. A previously reported analytical solution that considers both product shrinkage and variable diffusivity was generalized to describe the drying kinetics of food products with parallelepiped geometry. Selected drying experiments were then fitted to this solution using six different sets of model assumptions. Results indicated that product shrinkage is the main factor to be considered in order to estimate reliable values for diffusion coefficients. The OD pretreatments produced a significant reduction of the initial moisture content of chayote slabs before drying, thus allowing shorter drying time, which may lead to reduced energy consumption.

Hot Air Drying Characteristics of Fruits and Vegetables and Surface Hardening of Samples during Drying

Hot Air Drying Characteristics of Fruits and Vegetables and Surface Hardening of Samples during Drying

Air drying and colour characteristics of chestnuts pre-submitted to osmotic dehydration with sodium chloride

Air drying kinetics of chestnuts ( Castanea sativa Mill .) submitted previously to osmotic dehydration with sodium chloride solutions (22%, w/w, 25 °C, 8 h) were experimentally determined. Drying experiments were carried out at 45, 55 and 65 °C during 32 h. Before osmotic dehydration operation, shell and tegument tissue were carefully removed in all samples. Rough external surface was maintained (peeled samples) or also removed (cut chestnuts) in different tests in order to evaluate the effect of the presence of this layer in the mass transfer rate. A diffusional model involving shrinkage was employed to simulate the drying kinetics of the all studied systems and values of the effective coefficient of diffusion of water were obtained. These coefficients were successfully correlated with temperature by means of an exponential equation and were employed to evaluate the additional mass transfer resistances due to the presence of layers and by the acquisition of osmotic solute in cut and peeled samples. The experimental determination of local salt and moisture contents during drying showed the existence of a drying front for water that moves along from surface to the centre of the sample and that salt accumulates near surface but also achieve the centre during the osmotic dehydration. Additionally, the analyses of the surface colour of air dried samples indicated that osmotic dehydration with salt keeps the characteristics observed for non-treated cut samples and deteriorates the colour quality in the case of peeled samples.