Dehydration of Low-Grade Asparagus

ABSTRACT

Dehydration by a forced convection process is one potential method to add value to low-grade asparagus for marketing purposes. The objectives of this study were to determine the optimum drying temperature, air velocity, and predrying blanching treatment and study the effects of those parameters on the drying curves for low-grade asparagus and the efficiency of the drying process. The ranges of investigation were 60 to 93^°C and 0.14 to 0.44 m/s for drying temperature and air velocity, respectively. Drying at 51 ^°C and 0.30 m/s yielded product with an optimum quality, and drying at 79^° C and 0.18 m/s yielded the optimum process efficiency of 17.9%. Drying temperature, air velocity, and predrying blanching treatment all affected the rate of drying in the constant-rate drying period and the length of the constant-rate drying period. In the falling-rate period, all of the process parameters studied had some effect on the shape of the drying curve.     

微波真空干燥高粘度的灵芝浓缩液

热敏性、高粘度物料的干燥仍是现代干燥技术中的一个难题。灵芝水提后，由薄膜蒸发器浓缩至含水量70％左右，然后采用微波真空干燥（真空度3000Pa）至水分含量10％左右，改用传统的电热真空干燥（55～60℃）至含水量6％～7％。对干燥产品的主要生物活性成分——灵芝多糖和三萜酸进行了分析检测并与其它干燥方法进行了比较。结果表明：利用微波真空干燥的灵芝产品其灵芝多糖和三萜酸的保留率与冷冻干燥产品十分接近。而比传统真空干燥（60—65℃）的产品要高得多，此外采用微波真空干燥的干燥时间要短得多。     

Dehydration of Garlic Slices by Combined Microwave-Vacuum and Air Drying

Combination of microwave-vacuum drying and air drying was investigated as a potential mean for drying garlic slices. The sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional hot-air drying at the temperature of 45°C to final moisture content less than 5% (wet basis). Pungency, color, texture, and rehydration ratio of garlic slices dried by this method were evaluated and compared with those dried by freeze drying and conventional hot-air drying. The comparison showed that the quality of garlic slices dried by the current method was close to that of freeze dried garlic slices and much better than that of conventional hot-air dried ones. The lab microwave-vacuum dryer which the materials to be dried could be rotated in the cavity was developed by the authors.     

Modeling of Drying Curves for Some Foodstuffs Using a Kinetic Equation of High Order

Non-linear regression was used to fit a high order kinetic model to drying curves for mango and cassava. For comparison purposes, the same experimental data were also adjusted by non-lines regression to a model based on exponential series, and to another exponential model by simple linear regression. The high order model fit the experimental data with higher precision (r2 Al.98) than the other exponential series models. The proposed higher order model is mathematically simple as compared to the exponential series, and could be used for simulation of drying processes.     

Dehydration of Garlic Slices by Combined Microwave-Vacuum and Air Drying

Abstract

Combination of microwave-vacuum drying and air drying was investigated as a potential mean for drying garlic slices. The sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional hot-air drying at the temperature of 45°C to final moisture content less than 5% (wet basis). Pungency, color, texture, and rehydration ratio of garlic slices dried by this method were evaluated and compared with those dried by freeze drying and conventional hot-air drying. The comparison showed that the quality of garlic slices dried by the current method was close to that of freeze dried garlic slices and much better than that of conventional hot-air dried ones. The lab microwave-vacuum dryer which the materials to be dried could be rotated in the cavity was developed by the authors.     

Effects of anisotropic scattering of radiation in laminar forced convection in a parallel-plate duct

Effects of anisotropic scattering to heat transfer in hydrodynamically-developed, thermally-developing steady laminar forced flow of a gray fluid between two infinite parallel plates are investigated for the case when the inlet temperature of the fluid is less than the wall temperature. An implicit finite difference scheme is applied to solve the energy equation, while the high order P_N method is used to solve the radiation part of this problem. The effects of the anisotropy, the conduction-to-radiation parameter, the optical thickness, the reflectivity of the plates and the inlet temperature on the local Nusselt number are studied.     

Thermal Dehydration Methods for Fruits and Vegetables

Abstract

This paper presents the results of laboratory thermal drying of some vegetables and fruits including konjak, hawthorn, apple, vegetable seeds, garlic slices, bullion vegetable, and jujube. Different materials require different drying equipment and operating conditions as discussed in this article. The results are believed to be helpful for the selection and design of industrial dryers and the choice of appropriate operating conditions in processing these and similar materials.     

Dehydration of Concentrated Ganoderma lucidum Extraction by Combined Microwave-Vacuum and Conventional Vacuum Drying

Combination of microwave-vacuum drying and conventional vacuum drying was investigated as a potential method for drying concentrated Ganoderma lucidum extraction. The Ganoderma lucidum was extracted by hot water (60–65°C) and then concentrated to moisture of about 70% (wet basis) in a rising-film evaporator. The concentrated sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional vacuum drying at the temperature of 55–60°C to final moisture content about 6% (wet basis). The retention of polysaccharide and triterpenes of Ganoderma lucidum dried by this method were evaluated and compared with those dried by freeze drying and conventional vacuum drying alone. The comparison showed that the quality of extraction dried by the current method was close to that of freeze-dried extraction and much better than that of conventional vacuum-dried ones.     

Dehydration of Concentrated Ganoderma lucidum Extraction by Combined Microwave-Vacuum and Conventional Vacuum Drying

Combination of microwave-vacuum drying and conventional vacuum drying was investigated as a potential method for drying concentrated Ganoderma lucidum extraction. The Ganoderma lucidum was extracted by hot water (60-65°C) and then concentrated to moisture of about 70% (wet basis) in a rising-film evaporator. The concentrated sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional vacuum drying at the temperature of 55-60°C to final moisture content about 6% (wet basis). The retention of polysaccharide and triterpenes of Ganoderma lucidum dried by this method were evaluated and compared with those dried by freeze drying and conventional vacuum drying alone. The comparison showed that the quality of extraction dried by the current method was close to that of freeze-dried extraction and much better than that of conventional vacuum-dried ones.     

Modeling of Drying Curves for Some Foodstuffs Using a Kinetic Equation of High Order

ABSTRACT

Non-linear regression was used to fit a high order kinetic model to drying curves for mango and cassava. For comparison purposes, the same experimental data were also adjusted by non-lines regression to a model based on exponential series, and to another exponential model by simple linear regression. The high order model fit the experimental data with higher precision (r2 Al.98) than the other exponential series models. The proposed higher order model is mathematically simple as compared to the exponential series, and could be used for simulation of drying processes.     

褐煤干燥脱水技术的研究进展

本文首先介绍了褐煤的现状以及褐煤利用过程中存在的问题,然后提出了几种褐煤脱水工艺,如回转管式干燥技术、热脱水工艺、机械热压脱水(Mechanical and Thermal dehydration即MTE),过热蒸汽内加热流化床干燥(Super-heated steam Fluid bed low-rank Coal Upgrading简称SFCU)等,并分析了各自的特点,最后对SFCU工艺做了详细介绍。     

THE STUDY OF INTERRUPTED DRYING TECHNIQUE FOR ROUGH RICE

Abstract

The purpose of this research was to study the optimum strategy of the interrupted drying technique for rough rice. The effects of interrupted drying on drying rates, cracking enhancement ratios, and the performance of a commercial circulating rice dryer were evaluated. The results indicated that the required interrupted period of grains with moisture of ranging from 18 to 20% was 2 around 3 hours. The interrupted drying technique can significantly increase the drying rate. The dryer performance e.g. fuel-consumption rate, drying rate, and drying time were all affected by interrupting the drying process, as expected.     

Conditions of the Thermal Explosion under Forced Convection of a Reacting Mixture

Conditions of origination of the thermal explosion in a cylindrical chemical reactor equipped by a certain number of symmetrically located stirrers ensuring forced convection of the reacting mixture are considered in the approximation of an infinite Peclet number and under the assumption of laminar motion of the fluid. The critical value of the thermal explosion parameter (Frank-Kamenetskii parameter) is found as a function of the number of stirrers and the distance between the centerlines of the stirrers and reactor. As the number of stirrers increases, the calculations predict a lower probability of the thermal explosion, and the critical value of the parameter can severalfold exceed its classical value. It is found that the thermal explosion parameter substantially depends on the location of the stirrers, responsible for heat removal from the reactor. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 49–54, September–October, 2005.     

THE STUDY OF INTERRUPTED DRYING TECHNIQUE FOR ROUGH RICE

The purpose of this research was to study the optimum strategy of the interrupted drying technique for rough rice. The effects of interrupted drying on drying rates, cracking enhancement ratios, and the performance of a commercial circulating rice dryer were evaluated. The results indicated that the required interrupted period of grains with moisture of ranging from 18 to 20% was 2 around 3 hours. The interrupted drying technique can significantly increase the drying rate. The dryer performance e.g. fuel-consumption rate, drying rate, and drying time were all affected by interrupting the drying process, as expected.     

CRAPE DRYING : FROM SAMPLE BEHAVIOUR TO THE DRIER PROJECT

ABSTRACT

A drier project necessitates the efficient formulation of the behaviour of product samples. When the temperature gap is great, the drying rate must make explicit the influence of the thnc air parameters : temperature, moisture, velocity. The case of the grape demonsnates that the adimensional expression formulated by Van Meel and Keey. must be completed in order to be adjusted to experiments.

The hot air drier model composed of the equations of conservation and thin layer drying rate can sometimes be simplified into a form of analytic integral equation around the drying rate. W e drying can be considered generally as adiabatic.

Two examples of grape driers are presented and show the value of simplified tools for the project. In a tunnel drier with a high air temperature one can speak of the celerity of a drying front which progress along the trolleys. In a short drier connected to an agricultural solar collector, the integration of the drying rate takes into account the variation of the meteorological data.     

CRAPE DRYING : FROM SAMPLE BEHAVIOUR TO THE DRIER PROJECT

A drier project necessitates the efficient formulation of the behaviour of product samples. When the temperature gap is great, the drying rate must make explicit the influence of the thnc air parameters : temperature, moisture, velocity. The case of the grape demonsnates that the adimensional expression formulated by Van Meel and Keey. must be completed in order to be adjusted to experiments.

The hot air drier model composed of the equations of conservation and thin layer drying rate can sometimes be simplified into a form of analytic integral equation around the drying rate. W e drying can be considered generally as adiabatic.

Two examples of grape driers are presented and show the value of simplified tools for the project. In a tunnel drier with a high air temperature one can speak of the celerity of a drying front which progress along the trolleys. In a short drier connected to an agricultural solar collector, the integration of the drying rate takes into account the variation of the meteorological data.     

Heat and Mass Transfer Analogy Studies of Binary Liquid Mixture in Comparison with Eteanol-n-Heptane Evaporating to Air

ABSTRACT

An expenmental and theoretical study of heat and mass transfer analogy and a comparison of that to a binary liquid mixture evaporation is presented. Common organic solvents, ethanol and n-heptane, were used to form an alcohol - hydrocarbon mixture. Studies were carried out in a horizontal rectangular channel having air flow velocities of 0.2 – 0.9 m/s. Heat transfer coefficients were measured with a copper plate resistor and mass transfer coefficients with a square pool. The heat and mass transfer analogy is presented for a system having two evaporating compounds with a fixed value of air flow and verified by measuring and comparing mass transfer coefficients for distilled water with air flow velocities of 0.2 - 0.9 mls. An illustrative example of the use of the theory for industrial ventilation is presented.     

Heat and Mass Transfer Analogy Studies of Binary Liquid Mixture in Comparison with Eteanol-n-Heptane Evaporating to Air

An expenmental and theoretical study of heat and mass transfer analogy and a comparison of that to a binary liquid mixture evaporation is presented. Common organic solvents, ethanol and n-heptane, were used to form an alcohol - hydrocarbon mixture. Studies were carried out in a horizontal rectangular channel having air flow velocities of 0.2 - 0.9 m/s. Heat transfer coefficients were measured with a copper plate resistor and mass transfer coefficients with a square pool. The heat and mass transfer analogy is presented for a system having two evaporating compounds with a fixed value of air flow and verified by measuring and comparing mass transfer coefficients for distilled water with air flow velocities of 0.2 - 0.9 mls. An illustrative example of the use of the theory for industrial ventilation is presented.     

Quality of restructured cookies made from old stalks of Asparagus officinalis using various drying methods

The restructured crisp cookies were made from the old stalks of Asparagus officinalis. Temperature distribution, expansion ratio, moisture content, and color were measured to evaluate the drying uniformity of the cookies by applying pulse-spouted microwave-assisted vacuum drying (PSMVD) and microwave-assisted vacuum drying (MVD). Besides, bulk density, expansion ratio, microstructure, and textural properties were used to compare the products’ quality obtained by three different drying methods including vacuum drying, MVD, and PSMVD. Results showed that the products dried by PSMVD were more uniform compared to those samples dried by MVD. The pulse-spouted mode in drying chamber substantively improved the microwave-vacuum-dried products’ quality, drying uniformity, and drying characteristics.     

Drying of Seabuckthorn (Hippophae rhamnoides L.) Berry: Impact of Dehydration Methods on Kinetics and Quality

Convective hot air drying and freeze drying were investigated as potential dehydration processes to obtain powders of seabuckthorn fruit pulp. Halved seabuckthorn fruits were placed in a hot air dryer and dried at 1 m/s and at 50 or 60°C or freeze dried at less than 30 mTorr and at 20 or 50°C shelf plate temperature. An initial characterization of the seabuckthorn pulp (moisture, pH, soluble solid content, vitamins C and E, total phenolics, and carotenoids) was performed. Water loss, total phenolic compounds, total carotenoids, and vitamin C were determined at different processing times. Vitamin E was determined before and at the end of drying.

Freeze-drying kinetics were faster than air drying, probably due to lower moisture diffusion in the compact, sugary, and oily structure of the air-dried tissue. The temperature had an important impact on hot air–drying and freeze-drying kinetics. Drying method and processing times affected the remaining phenolic, carotenoid, and vitamin contents of seabuckthorn berries. Freeze drying was revealed as a superior method to obtain seabuckthorn powders because of the lower residual moisture content, the ease of grinding, as well as the better nutritional retention.