CONVECTIVE DRYING OF PUMPKIN: INFLUENCE OF PRETREATMENT AND DRYING TEMPERATURE

The aim of this research was to study the influence of blanching as a pretreatment on the drying rate, color and rehydration rate of pumpkin slices ( Cucurbita maxima ) dried in a convective dryer at 50, 60 and 70C.
The different pretreatments did not modify drying time. The diffusion coefficient depended on temperature and moisture content, but not on pretreatments. It varied between 1.6 and 2.9  ×  10⁻⁹ m²/s and activation energy was approximately 35.6 kJ/mol. The rehydration rate of the dried sample, which was found to be influenced by drying temperature but not by the pretreatments, reached about 2 kg water/kg dry solid in about 150 s in boiling water. Color parameters " L " and " b " were influenced by drying temperature and pretreatments. Parameter L varied between 36 and 53 and parameter b varied between 20 and 31. Samples dried at 70C without pretreatments presented color parameter values very similar to those of the fresh sample.

PRACTICAL APPLICATIONS

This work evaluates the pretreatment and drying conditions of pumpkin. Five parameters of the optimal product are considered: pretreatment time, drying time, temperature, color and rehydration rate of the product. With these results, drying of pumpkin can be carried out in industrial convective dryers and the dried product may be used in the preparation of soups, premixed foods, snacks, etc.     

THIN-LAYER DRYING OF DATES

Thin‐layer drying rates of two date cultivars, namely, Sukkari and Sakie were experimentally determined at three drying temperatures 70, 80, and 90C. Three drying models were evaluated for the thin‐layer date data. These were the exponential model, Page equation, and the approximation of diffusion model. The Page equation fitted the data best. Two empirical expressions of Page equation for predicting moisture ratio as a function of drying time and drying temperature for the two date cultivars are presented.     

RADIO-FREQUENCY DRYING OF TEXTILES

An account is given of the radio-frequency drying of textiles and of its advantages in comparison with conventional drying methods. Its use in the drying of yarn packages, loose stock, and sliver is described, and comparative costs of the different systems are discussed.     

THROUGH-CIRCULATION DRYING OF TAPIOCA ROOT

SUMMARY— The drying characteristics of fresh/y harvested tapioca root (Manihot utilissima Pohl) from Posadas, Argentina, have been investigated in a laboratory through-circulation dryer. Variables studied were bed depth (2-12 cm), air velocity (2,300-5,200 kg/(hr)(sq meter), and air temperature (55—100°Cl. Static pressure drops of air passing through beds of dried and wet slices also were investigated. Straight lines are obtained plotting on semilogarithmic paper the nondimensional moisture content (W-We) (Wo-We) against time. This allows deduction that a diffusional mechanism is controlling the drying rate. Factors to be considered in the design of a continuous through-circulation dryer are given.     

IMPINGEMENT DRYING OF POTATO CHIPS

The effect of superheated steam temperature (115, 130, and 145C) and convective heat transfer coefficient (100 and 160 W/m²C) on the drying rate and product quality attributes (shrinkage, density, porosity, color, texture, and nutrition loss) of potato chips was investigated. Furthermore, potato chips dried by impinging superheated steam (130 and 145C, h = 100 W/m²C) were compared to air dried (same conditions), commercial, and fried potato chips. Temperature and convective heat transfer coefficient had a significant effect on the drying rate during superheated steam impingement drying. Potato chips dried at higher drying temperature and convective heat transfer coefficient showed less shrinkage, lower bulk density, higher porosity, and darker color when compared to chips dried at lower temperatures and convective heat transfer coefficients. They were also less hard and had a lower vitamin C content. A higher rate of evaporation during the falling rate period was obtained when superheated steam drying was compared to air impingement drying. Potato chips produced using superheated steam impingement drying showed more shrinkage, higher bulk density, lower porosity, and lighter color than chips dried with air under the same temperature and with the same convective heat transfer coefficient (130, and 145C, h = 100 W/m²C). Moreover, superheated steam‐dried potato chips retained more vitamin C during the drying process.     

优质稻谷保鲜干燥方法研究

将水分为16.0%～18.6%的新收割优质稻谷采用包装打围、中间散存的方式储藏,分别使用热风就仓干燥,自然风就仓干燥和低温储藏干燥等方法进行干燥处理,同时也使用低温烘干机和自然晾晒等方法进行干燥处理。结果表明:各种干燥处理都达到了满意的效果,达到预期干燥水分,干燥均匀,未增加裂纹粒(爆腰粒),发芽率、黄粒米率、整精米率、脂肪酯值和粘度等重要品质指标未发生明显变化,品质新鲜。通过试验找到了稻谷保鲜干燥方法,可与保鲜储藏稻谷的方法配套,为保鲜大米加工常年提供新鲜稻谷原料。     

DRYING KINETICS OF RED PEPPER

Desorption isotherms of unblanched and blanched red peppers were experimentally obtained at 30C. The desorption data were exploited to estimate equilibrium moisture contents of the peppers at drying temperatures other than 30C by using a semi-empirical method. Red pepper samples were dried in a tunnel-type drier with an air velocity of 2 m/s at 50C, 60C, 70C, and 80C. The blanched samples dried faster than the unblanched ones. The drying behavior of unblanched and blanched samples was characterized by falling rate period, and constant and falling rate drying periods, respectively. The interphase mass and heat transfer coefficients of the blanched sample during the constant rate period were not affected by temperature and estimated to be 1.94*10⁻³ kg mol/s. m² and 57.3 W/m². K, respectively. Effective moisture diffusivity was estimated between 6.83*10⁻¹⁰−17.4*10⁻¹⁰ m²/s for the unblanched sample and 11.4*10⁻¹⁰−31.0*10⁻¹⁰ m²/s for the blanched sample within the given temperature range. Effect of temperature on the diffusivity was described by an Arrhenius-type equation with an activation energy of 28.4 kJ/mol for the unblanched pepper and 33.3 kJ/mol for the blanched pepper.     

DRYING BEHAVIOR OF CULTURED MUSHROOMS

In this study, the drying behavior of cultured mushrooms with an initial moisture content of 93% (drying basis [ d.b. ]) was investigated experimentally for different slice thicknesses and drying air temperatures, and the suitability of various drying models in defining the drying behavior of mushrooms was determined by statistical analysis. Drying operation was carried out at temperatures of 40, 45, 50 and 60C and at a fixed air velocity of 2 m/s. The slice thicknesses of mushrooms were taken as 2, 4 and 6 mm. The experimental results show that the drying temperature has a significant effect on the moisture removal from mushrooms. However, it is also observed that increasing the temperature above a certain value for large values of slice thickness does not have a considerable effect on the drying rate. It may also be concluded from the experimental results that the increase in the slice thickness slows down the drying rate significantly. Furthermore, the results of statistical analysis show that the most suitable model in defining the drying behavior of mushrooms is the diffusion approach model.

PRACTICAL APPLICATIONS

Mushrooms are soft textured and extremely perishable. They begin to deteriorate shortly after harvest. Because of their short shelf life under normal ambient conditions of temperature and humidity, their preservation has assumed importance. The most common species that is also grown on a large scale in Turkey is the cultivated mushroom, Agaricus bisporus . They are low in calorie and have a delicate, appealing flavor. They contain about 91% water. Drying is the most common preservation method, especially for mushrooms to be used as ingredients for special sauces and soups. Preservation of mushrooms through drying makes it possible to limit microbial growth or other reactions by reducing moisture content, and allows efficiency in transportation and storage.     

EVALUATION OF THIN-LAYER DRYING MODELS FOR DESCRIBING DRYING KINETICS OF BARBERRIES (BARBERRIES VULGARIS)

Barberry is known as a medicinal and ornamental plant throughout the world. Edible fruit from the barberry is used in medicine to treat liver, neck and stomach cancer, for purification of the blood and for breath freshness. In order to assess and select a suitable form of the drying curve, six different semitheoretical and/or empirical models were fitted to the experimental data. Experiments were performed at air temperatures of 50, 60 and 70C. At each temperature, three air velocity values were selected: 0.5, 1 and 2 m/s. Consequently, of all the drying models, the Page model was selected as the best mathematical model according to R ², χ ² and root mean square error parameters. Constants related to the Page model are reported and regressed against air condition using multiple regression analysis.

PRACTICAL APPLICATION

All commercial flow dryers are designed on thin-layer drying principles. Thin-layer drying means to dry as one layer of sample particles or slices. In this paper we present a mathematical model for thin-layer drying of barberry fruits (moisture ratio against time). Definition of moisture ratio as a function of time and drying condition has many advantages such as (1) easy control of dryer system, (2) lower energy consumption, (3) less thermal damage to the products and (4) lower investment. It is believed that the present study should be useful to people seeking (1) to optimize the design of drying systems and their components, and (2) to identify appropriate applications and optimal configurations for drying systems.     

食品过热蒸汽干燥的研究进展

介绍了过热蒸汽干燥的基本理论和特点.从模拟研究和实验研究两个方面综述了食品过热蒸汽干燥的研究进展,重点介绍了过热蒸汽在各种干燥机上对不同物料的干燥,以及与其他干燥方式相结合对不同物料的干燥,并提出进一步研究的建议.     

MICROWAVE FINISH DRYING OF POTATO CHIPS

The effect of microwave finish drying of potato chips on their texture, color and oil content was studied. The intermediate moisture content (IMC) of the chips before microwave application and the reducing sugar content of the raw potatoes were the primary variables. The slices were individually submerged in oil at 320° F to various IMC and finish dried with 2500 watts microwave power for 1–3 min. Chip color was rated against PC11 Color Standards. Texture was evaluated subjectively by a panel and objectively by the L.E.E. Kramer Shear Press. Oil determination was made by Soxhlet extraction. The results showed that potato chips removed from the oil at IMC above 13% were unacceptably tough after microwave drying. Potatoes containing more than 0.9% reducing sugar had to be removed from the oil at IMC above 13% in order to obtain acceptable color of the microwave-finished product. Therefore, microwave finishing raises the limiting reducing sugar content from about 0.4 to about 0.9%. Oil content of microwave-finished chips was 90% that of conventional controls     

花粉热风干燥特性研究

通过对花粉在不同干燥温度（T）、花粉厚度（h）条件下干燥实验,建立了花粉热风干燥的数学模型：MR=aexp（-kdt）其中：a=exp（0.0566T＋0.4044h-3.3586）;kd=-0.0003T＋0.1776h-0.5321