DRYING BEHAVIOR OF MUSHROOM SLICES

Drying of mushroom slices is an unsteady-state process under the control of diffusion race of water through the mushroom hyphae. Therefore, temperature, thickness of the mushroom slices and the ratio of the air film to mushroom resistance toward the diffusion of water control the drying rate. In this work, the initial thickness of mushroom slices was kept constant at 2 mm and the effects of structural parameters, temperature and humidity were investigated. Through the measurements of weight, center and surface temperatures of the mushrooms, and variation of the surface area, actual drying behavior of mushrooms under different dryer conditions were determined. Color of the dried mushroom slices were used as criteria for the evaluation and determination of the optimum conditions.     

茭白片热风对流干燥模型与传质性能

为了探讨茭白干燥的传递特性,在对流热风干燥实验装置中进行了茭白片薄层干燥实验,研究了干燥温度、片的厚度对干燥过程的影响,将试验的水分比与数学模型进行了拟合,计算了不同温度下的水分扩散系数,并关联了其与干燥温度的关系.结果表明:干燥温度对干燥过程影响显著,薄片有利于水分扩散:用Page模型来描述茭白片热风干燥动力学令人满意;茭白片厚度为0.003m时,随风温升高,水分扩散系数从3.440×10-9 m2·s-1增大到6.357×10-9m2·s-1,并符合阿累尼乌斯方程,活化能为27.86 kj·mol-1.相同温度下,物料中水分的扩散系数基本不受厚度影响.     

LOW TEMPERATURE MUSHROOM (A. bisporus) DRYING WITH DESICCANT DEHUMIDIFIERS

ABSTRACT

Cultivated mushrooms (Agaricus bisporus) slices of 2·5 and 5 mm thick were dried with dehumidified air at 20°, 30° and 40°C. Rehydration ability of dried mushrooms was used as criteria for the evaluation and determination of optimum conditions. Drying mechanism of the mushroom slices was expressed by unsteady state diffusion and the results were interpreted by Fickian model. Drying temperatures lower than 40°C promoted the production of light coloured mushrooms with high rehydration ratios. Diffusivity constants were in the range of 2·6?12×l0^-11 m²/s and the activation energies varied in the range of 23·5?30·3 kJ/gmol depending on the temperature and sample thickness.     

EFFECT OF PRETREATMENT AND DRYING ON THE QUALITY OF OYSTER MUSHROOMS (PLEUROTUS OSTREATUS)

Fruiting bodies of oyster mushroom were dried by hot-air drying, vacuum-drying and freeze-drying in order to compare food qualities after drying. Prior to drying, mushrooms were subjected to blanching or dipping in sodium metabisulphite solution (1 or 5 g/L), or dipping in citric acid solution (1 or 5 g/L). Drying of raw mushrooms was taken as a control. Blanching reduced the attractiveness of dry mushrooms; sodium metabisulphite improved it. It has been found that pretreatment and drying method affect the course and rate of drying. Samples subjected to hot-air drying and vacuum-drying were darker than those freeze-dried, which were clearly more attractive. The hot-air and vacuum-dried mushrooms on rehydration were inferior in quality to the freeze-dried samples. Flavor of the freeze-dried mushroom was not significantly different from that of the hot-air dried mushrooms. Food quality of dried mushrooms depends significantly on the type of drier used.     

EFFECT OF PRETREATMENT AND DRYING ON THE QUALITY OF OYSTER MUSHROOMS (PLEUROTUS OSTREATUS)

Fruiting bodies of oyster mushroom were dried by hot-air drying, vacuum-drying and freeze-drying in order to compare food qualities after drying. Prior to drying, mushrooms were subjected to blanching or dipping in sodium metabisulphite solution (1 or 5 g/L), or dipping in citric acid solution (1 or 5 g/L). Drying of raw mushrooms was taken as a control. Blanching reduced the attractiveness of dry mushrooms; sodium metabisulphite improved it. It has been found that pretreatment and drying method affect the course and rate of drying. Samples subjected to hot-air drying and vacuum-drying were darker than those freeze-dried, which were clearly more attractive. The hot-air and vacuum-dried mushrooms on rehydration were inferior in quality to the freeze-dried samples. Flavor of the freeze-dried mushroom was not significantly different from that of the hot-air dried mushrooms. Food quality of dried mushrooms depends significantly on the type of drier used.

     

AIR-DRYING OF FRESH AND OSMOTICALLY PRE-TREATED PINEAPPLE SLICES: FIXED AIR TEMPERATURE VERSUS FIXED SLICE TEMPERATURE DRYING KINETICS

In this investigation, the air drying characteristics of fresh and osmotically pre-treated pineapple slices in a tray dryer were studied under different operating conditions. The air velocity varied from 1.5 to 2.5 m/s and the air temperature from 40 to 70°C. The analytical solution of the second Fick's law for an infinite slab was used to calculate effective diffusion coefficients and their temperature dependence could be well represented by an Arrhenius-type equation. Comparison of the results showed that the diffusion coefficients were lower for the pre-treated fruit. By means of automatic control, it was possible to obtain drying curves under conditions of constant product temperature, which showed to be an alternative to reduce the drying time of pineapple slices.     

Process Drying Practice

In this investigation, the air drying characteristics of fresh and osmotically pre-treated pineapple slices in a tray dryer were studied under different operating conditions. The air velocity varied from 1.5 to 2.5 m/s and the air temperature from 40 to 70°C. The analytical solution of the second Fick's law for an infinite slab was used to calculate effective diffusion coefficients and their temperature dependence could be well represented by an Arrhenius-type equation. Comparison of the results showed that the diffusion coefficients were lower for the pre-treated fruit. By means of automatic control, it was possible to obtain drying curves under conditions of constant product temperature, which showed to be an alternative to reduce the drying time of pineapple slices.     

The Thin-Layer Drying Characterstics of White Onion Slices

ABSTRACT

A batch–type experimental dryer with a computer–aided data acquisition system was designed and built for the thin layer drying studies of onion (Allium cew L., cv. Southport White Globe) slices. Twenty seven single–layer drying curves were established for a temperature range of 42.5–90⁰C, an air velocity range of 0.6–1.4 m/s, an air humidity range of 0.0093–0.0442 kg of water/kg of dry air: and a slice thickness range of 0.002–0.005 m. The single–term exponential model adequately described the single–layer drying behaviour of the onion slices. l'he dependence of the drying rate constant on air temperature, absolute humidity, velocity and on slice thickness was best explained by an Arrhenius–type relationship. The drying rate constant in which moisture diffusion and shrinkage effects are lumped was greatly influenced by the sample thickness and drying air temperature, and to a lesser extent, by the air humidity and velocity.     

The Thin-Layer Drying Characterstics of White Onion Slices

A batch-type experimental dryer with a computer-aided data acquisition system was designed and built for the thin layer drying studies of onion (Allium cew L., cv. Southport White Globe) slices. Twenty seven single-layer drying curves were established for a temperature range of 42.5-90⁰C, an air velocity range of 0.6-1.4 m/s, an air humidity range of 0.0093-0.0442 kg of water/kg of dry air: and a slice thickness range of 0.002-0.005 m. The single-term exponential model adequately described the single-layer drying behaviour of the onion slices. l'he dependence of the drying rate constant on air temperature, absolute humidity, velocity and on slice thickness was best explained by an Arrhenius-type relationship. The drying rate constant in which moisture diffusion and shrinkage effects are lumped was greatly influenced by the sample thickness and drying air temperature, and to a lesser extent, by the air humidity and velocity.     

Kinetic and Quality Study of Mushroom Drying under Microwave and Vacuum

Abstract

The aim of this work is to model the drying kinetics of mushrooms under several operational conditions, to evaluate the effective diffusivity coefficient of moisture removing by a drying model and inverse calculus method in finite differences and to study the effect on the final quality of dehydrated mushrooms. Different ways of microwave vacuum drying were compared to freeze-drying. Results show that a decrement of the applied pressure produces a certain increase in the drying rate together with a lower moisture in the dehydrated product at the end. Temperature control inside the sample helps to ensure a better quality in the dehydrated product, than when controlled at the surface. Diffusivity coefficients show a correspondence with product temperature during drying. The microwave dried samples obtained with moderate power and temperature control of product shown an important degree of quality similar to that obtained by freeze-drying.     

Water status and distribution in shiitake mushroom and the effects of drying on water dynamics assessed by LF-NMR and MRI

Abstract

Water status and distribution in shiitake mushroom and the effects of drying temperature on water migration were investigated by low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) technique. Three water components assigned to bound, immobilized water and free water were observed in fresh shiitake mushroom by LF-NMR, and higher moisture content was found in the lamella and outer layer of stalk by MRI. During drying, the transverse relaxation time and peak area of immobilized and free water in pileus significantly decreased. Higher drying temperature could promote the changes in water mobility and population. MRI results revealed the water evaporated from external surface of shiitake mushroom, then the water in inner region migrated to the surface during the drying. The drying properties, color and shrinkage of shiitake mushroom were also measured. The strong correlation between moisture content and total peak area of water with a coefficient of 0.9792 revealed the potential of LF-NMR as a rapid and nondestructive method to monitor drying degree of shiitake mushroom.     

Drying of Mushroom Slices Using Hot Air Combined with an Electrohydrodynamic (EHD) Drying System

In this study, hot air combined with EHD drying is examined as an improved method for drying mushroom slices. The effects of three levels of voltage (17, 19, and 21 kV) and electrode gap (5, 6, and 7 cm) on the drying kinetics, time, effective water diffusion coefficient, and energy consumption of the EHD, pure hot air (provided within a chamber), and hot air combined with EHD drying systems were investigated. ANOVA showed that there were significant differences between EHD treatments and control (pure hot-air-drying treatment) for all of the investigated responses. Voltage and electrode gap factors had significant effects on all investigated responses. The results confirmed that the combination of EHD and hot air can significantly reduce the drying period, resulting in a greater effective water diffusion coefficient and drying rate and reduced energy consumption. As such, this technique offers a promising solution to the considerable energy consumption of the drying industry.     

Vacuum Drying of Oak Wood

ABSTRACT

Vacuum drying, j,e drying under absolute gas pressure of about 10? Pa. is an efficient means of reducing the process period and of producing good quality wood. We will examine here continuous vacuum drying where the plank surfaces are kept at a constant temperature, which remains above the boiling point, and moisture flowing to the surface is extracted from the kiln.

We have carried out an experimental study of oak drying under such conditions. The drying rate and moisture content profile of the sample (40 mm thick) are recorded during the whole drying period.

A model of continuous drying is established from general conservation equations with the main approximation that the air is rapidly extracted. The two constitutive equations of the model which describe temperature and water content fields are of a diffusive type and coupled through coefficients. The adequate boundary equation is not a convective one, but expresses a hygroscopic equilibrium between the vapour in the chamber and the wood surface. The mass diffusive coefficient can be adjusted to the drying rates through capillary pressure and bound water diffusion functions. The wood heterogeneity (seasonal growth) is the main factor of discrepancy in these functions. The simulated drying rates correspond with the experimental ones.     

The Effect of Glass Transition Temperature on the Procedure of Microwave–Freeze Drying of Mushrooms (Agaricus bisporus)

Freeze drying (FD) yields the best quality of dried mushroom but at the cost of a long drying time and high overall cost. Air drying (AD) gives an unacceptably poor quality product. To achieve faster drying along with a high-quality product, a microwave–freeze drying (MFD) technique was developed to dry mushrooms. The relationship between dried mushroom quality and the glass transition temperature during the MFD process was studied to optimize the MFD process. According to the change tendency of the glass transition temperature of mushroom during MFD, a step-down microwave loading scheme for the MFD process was developed to obtain good product quality.     

聚酰胺酸溶液成膜过程中的传质行为

为了研究聚酰胺酸溶液成膜过程中的传质行为,采用自制液膜干燥实验装置在线测定聚酰胺酸溶液质量的变化.假设气、液两相传质通量相等的条件下,计算了溶剂气相传质系数和液面蒸气压.在此基础上考察了干燥温度、液膜厚度、溶液相对分子质量对液膜表面蒸气压的影响.结果表明,成膜过程中存在溶剂蒸发与聚酰胺酸溶液亚胺化反应的相互竞争.干燥初期溶剂蒸气压迅速升高,液膜表面溶剂的扩散为控制步骤;而干燥后期溶剂蒸气压较小,溶剂在膜内部扩散成为控制步骤.同时随着液膜厚度的增加、干燥温度的升高及溶液相对分子质量的减少,液面蒸气压的最大值呈现增大趋势.     

Artificial neural network approach for protection of the color of dried golden and pink oyster mushrooms with pretreatments

In this study, the possibilities of protecting the color of dried golden and pink mushrooms were investigated, and color parameters of dried mushrooms were modeled by artificial neural network (ANN). For this purpose, first, the golden oyster mushroom (Pleurotus citrinopileatus) and pink oyster mushroom (Pleurotus djamor) were cultivated. Then, pretreatments were applied using citric acid (CA) and potassium metabisulfite (KMS) with different rates (0.5%, 1.0%, and 1.5%) separately, excluding control group mushrooms. All mushrooms were dried for 330 minutes in a laboratory type oven at two different temperatures (40°C and 50°C) until completely dehydrated. Colorimetric values (L*, a*, and b*) were determined using Konica Minolta CM‐2600d spectrophotometer for 30 minute intervals during the drying process. The obtained data were modeled using the ANN technique. The results show that darkening of mushrooms increased as the drying temperature increased. CA and KMS showed better results for dried golden and pink mushrooms, respectively. Thanks to the pretreatment, the mushroom's original color was protected compared with control samples. All mean absolute percentage error values of models were determined, which were lower than 4.0%. It was concluded that ANN can be a good way to predict the color of dried golden and pink mushrooms (pretreated or not) with a high degree of accuracy.     

Optimization of microwave-assisted fluidized-bed drying of carrot slices

The drying of carrot slices in a microwave-assisted fluidized-bed drying (MWFBD) system was investigated. The drying conditions such as the initial microwave power density and the inlet air temperature were optimized. The effects of different pretreatment processes such as water blanching, osmotic drying with 20% sugar solution, and 1% citric acid solution on the drying of carrot slices were investigated under the optimized drying conditions. The drying kinetics and the physical properties of the dried carrot slices were analyzed. Different mathematical models of the drying process were explored and fitted to the drying of carrot slices in MWFBD. The pretreatment of the carrot slices reduced the drying time required and improved the qualities such as color and textural strength of the dried carrot slices.     

Effects of Heating Conditions on the Thermal Denaturation of White Mushroom Suitable for Dehydration

White mushrooms suitable for drying are thermolabile materials. At present, the determination of thermal denaturation of dehydrated white mushroom mainly depends on the drying technology. To choose the appropriate dehydration technology for thermal analysis, differential scanning calorimetry (DSC) was used for determining the denaturing temperature range. White mushrooms at five different moisture content levels were chosen for the DSC tests. Five heating rates were used to observe the change of the denaturing ranges. Finally, the effects of short-term storage and instantaneous increases in temperature on the change of denaturing areas are discussed.     

Thin-Layer Drying of Flax Fiber: I. Analysis of Modeling Using Fick's Second Law of Diffusion

Thin-layer drying of moist flax fiber was performed at four temperatures of 30, 50, 70, and 100°C with a constant absolute humidity of 0.0065 kg water per kg dry air. The coefficients of diffusion of the fiber at different drying conditions were estimated by modeling the drying process using the one- to five-term solutions of the second Fick's law of diffusion. The models underestimated the drying process during the initial stages of drying and overestimated this process during the final stages. The estimated coefficient of diffusions ranged from 5.11 × 10^-9 to 1.92 × 10^-8 m²/s and linearly increased with the drying air temperature.