Osmotic dehydration of raspberries with vacuum pretreatment followed by microwave-vacuum drying

Defrozen raspberries were osmotically dehydrated in sucrose solution initially at low pressure (1.33 kPa for 8 min), and then at ambient pressure (4 h). Moisture decreased from 84% to 49% (wet basis), and almost one half of water removal occurred at the vacuum period. Two different transport coefficients were obtained: 19.9 × 10⁻¹⁰ m²/s for transport of water under vacuum, and 3.2 × 10⁻¹⁰ m²/s for water transport at atmospheric pressure. Losses of vitamin C were high (80%) and reutilization of sucrose solution is suggested. Osmotically dried raspberries were microwave-vacuum dried (1.33 kPa for 40 min) under on–off temperature control by varying microwave settings. An undamaged dried product (7.8% wet basis) of high quality (color, taste, structure) was obtained.     

Modelling shrinkage and porosity during vacuum dehydration

Summary  Apparent density, true density, specific volume and internal porosity were investigated during vacuum dehydration of banana, apple, carrot and potato, at various moisture contents and pressures. The pressure was found to effect significantly the apparent density and porosity of the materials examined, while for the true density, this effect was practically negligible. In all four materials the development of porosity was favoured by the decrease of pressure. At the lowest pressure used (30 mbars) banana and apple developed the highest porosity values (∽75%), followed by those of carrot (∽50%) and potato (-25%). A simple mathematical model was proposed to predict the above properties as functions of material moisture content and pressure. The parameters incorporated into the model were: the enclosed water density, the dry solids density, the apparent density of the dry material, and a transformed volume-shrinkage coefficient. Among these parameters, only the apparent density of the dry material was found to be strongly affected by the pressure and a suitable exponential equation was proposed to express this influence. The proposed model was fitted to the experimental data satisfactorily, and the required parameters were estimated through a regression analysis procedure.     

Influence of energy input and initial moisture on physical properties of microwave-vacuum dried strawberries

In microwave-vacuum drying, thermal energy is replaced by electric energy for heating the material. The additional application of a sufficient vacuum results in a gentle treatment, and specific product features such as aroma and flavor components, and color can be conserved. A crisp texture results from puffing due to expansion when moisture evaporates within the product, and is related to porosity. Using strawberries, a statistical central composite design was applied to relate specific drying energy and evaporation rate as well as raw and bulk density, and particle size distribution to absorbed microwave power input ranging from 2.4 kW kg⁻¹ to 10.5 kW kg⁻¹ dry matter, and to an initial moisture content of 0.17 kg kg⁻¹ to 0.73 kg kg⁻¹ on dry basis, achieved by convective predrying. A low initial moisture content and high microwave power lead to products with low density, porous structure and optimum puffing effects, but shows disadvantages with respect to moisture evaporation rate and energy utilization. On the other hand, optimum efficiency results from the use of raw materials with a high initial moisture content and from applying a high microwave power input.

The influence of powder morphology on the effect of rosemary aroma microencapsulation during spray drying

The influence of particle morphology of spray dried powders obtained by using different carriers on the efficiency of microencapsulation of rosemary aroma is shown in the present research. It was found that the type of the carrier influenced the size but not the shape of rosemary aroma capsules and all the capsules were spherical with cracks. The biggest particles, d₅₀ = 55 μm, were obtained with 25% maltodextrin (MD) as a carrier, and the smallest, d₅₀ = 29 μm with 30% gum arabic (GA). The efficiency of encapsulating aroma inside of the capsules depended on the particles size and apparent density. An increase in the quantity of microencapsulated aroma from 10% for 25% MD to about 60% for 30% GA as the carrier was seen, which co‐related with a decrease in the average diameter of the powder particles. Similarly, an increase in the efficiency of aroma retention was followed by an increase of apparent density of powders from 796 (25% MD) to 1156 kg m^?3 (30% GA).     

应用冻干技术加工食用菌制品

简析了食用菌快速发展形势,概述了真空冷冻干燥技术原理及产品特点,以香菇为例阐述了应用冻干技术加工食用菌制品所需的主要设备、生产工艺流程及操作要点,并对冻干食用菌产品标准进行了研究介绍。     

不同干燥方式对双孢蘑菇干制品质量的影响

对双孢蘑菇进行热风、真空和真空冷冻干燥的对比实验,建立了3种干燥方式下物料的干燥曲线,测定干制品Vc含量、复水比和感官质量。结果表明:从干燥效率和干制品Vc含量看,真空干燥>真空冷冻干燥>热风干燥;从复水比看,真空冷冻干燥>真空干燥>热风干燥,其中真空冷冻干燥的干制品感官质量最好。对干制品进行护色和复水实验,结果显示干制品护色质量好于不护色,复水时间直接影响复水程度,最佳复水时间为40min。     

超声波处理对香菇冷冻干燥过程的影响

针对目前香菇进行深加工采用的热风干燥以及腌制等加工手段,造成其产品外观质量差,严重影响其商品价值的情况,采用真空冷冻干燥方法。为了缩短香菇冷冻干燥时间,对香菇进行超声波预处理,发现经正交试验优化后的超声波预处理(超声波功率300 W,处理时间10min,脉冲5s∶3s)可提高香菇冷冻干燥速率,使其干燥时间缩短29.4%,而且可以获得更好的复水性(可提高约29%)。     

A fundamental approach and its experimental validation to simulate density as a function of moisture content during drying processes

Although several empirical models are available in the literature to predict density in solid matrices, only a very limited number of theoretical models have been reported. So far, no model considered the possible variation in the initial air volume existing at the beginning of the drying process. In this contribution, a theoretical model to predict bulk density of dried materials was built by considering two mechanisms that might occur during drying processes. These mechanisms are represented by collapse and shrinkage functions. The predictions obtained by this theoretical model were extensively validated with experimental data published by several independent groups for different food products dried with different technologies. In all these cases, the model gave excellent agreement with the experimental data regardless the topology of the curve bulk density versus moisture content. The model was also compared with other published models. The result of this comparison revealed that the errors resulting from the predictions obtained by the present model are among the smallest. Shrinkage and collapse functions were used to analyze the mechanisms by which bulk density varies during air-drying and freeze-drying. The model showed that both shrinkage and collapse phenomena are dramatically involved during air-drying. However, in the case of freeze-drying, no collapse is observed and only partial shrinkage is taking place. Hence, the present model can be used as a tool to predict the bulk density with excellent accuracy, to understand the dynamic mechanisms involved during drying. Moreover, this model can be incorporated to other models involving the variation of density as a function of moisture.     

Effect of temperature on rheological characteristics of molasses: Modeling of apparent viscosity using Adaptive Neuro - Fuzzy Inference System (ANFIS)

In this study, the effect of temperature on the rheological characteristics of apricot and date molasses was studied separately. Rheological characteristics of both molasses were evaluated in the shear rate range of 0.1-100 s⁻¹ at different temperatures (10-40 °C). Power law model was used for the calculation of flow behavior index and consistency coefficients of molasses. Consistency coefficients of apricot and date molasses were in the range of 5.408-39.905 Pa sⁿ and 0.910-2.852 Pa sⁿ, respectively. Molasses samples showed a non-Newtonian flow behavior. The effect of temperature on apparent viscosity was described by Arrhenius equation and calculated activation energy at the shear rate of 54.2 s⁻¹ was 41.42 and 38.19 kJ/mol for apricot and date molasses, respectively. An efficient predictive model for apparent viscosity values of molasses was constructed using Adaptive Neuro - Fuzzy Inference System (ANFIS) and this model showed satisfactory prediction with high coefficient of determination (0.979-0.999) and low root mean squared error (0.12-0.46).     

Modeling and minimizing process time of combined convective and vacuum drying of mushrooms and parsley

The aim of this work was to obtain a technological and economic alternative for mushroom and parsley dehydration combining convective and vacuum drying. Depending of product, this combination of technologies allows minimization of total drying time and avoids negative effects on quality of thermo-sensitive products during drying. Experimental drying curves were determined in a cross-flow convective dryer and in a cabinet vacuum dryer at 35, 45 and 55 °C. The most appropriate theoretical models were obtained and applied for combined processes in order to minimize the overall drying time and avoid final product damage. For parsley at the highest temperature (45 °C), reductions of 63% and 16% in drying time were observed with the combined drying process compared to the sole convective and sole vacuum drying, respectively. This reduction in process time was obtained when dryer change was done at the intermediate moisture condition that determines the highest drying rate during the whole combined process of convective and vacuum drying. For mushrooms, convective drying throughout the process, at the highest temperature (55 °C) compatible with product visual quality, minimized drying time.     

Mass Transfer Modeling and Shrinkage Consideration during Osmotic Dehydration of Fruits and Vegetables

During osmotic dehydration of fruits and vegetables, as water and/or other substances are removed from the material, shrinkage follows depending on the extent of net mass loss. Mass transfer is usually predicted through modeling. However, common models developed for osmotic dehydration of fruits and vegetables make assumptions that often deviate far from reality, including large heterogeneity, variability and complexity in properties of fruits and vegetables. This generates some skepticism about such models and minimizes their potential industrial reliability. This paper reviews osmotic dehydration of fruits and vegetables through a basic approach, provides a critical view on modeling and points out the factors that affect shrinkage and mass transfer based on an extensive evaluation of pertinent literature.     

Comparative study of different combined superheated-steam drying techniques for chicken meat

The purpose of this study was to compare and evaluate different drying techniques for chicken meat, which was aimed as an ingredient for ready-to-eat noodle. Two multi-stage drying techniques, i.e., superheated steam drying in the first stage followed by heat pump drying in the second stage (SSD/HP), and superheated steam drying in the first stage followed by hot air drying in the second stage (SSD/AD), were proposed. The effects of superheated steam temperature and moisture content of chicken at the end of the first-stage drying on the drying kinetics and quality of the dried product viz. color, shrinkage, rehydration ability were then evaluated. The results were also compared with those of purely superheated steam drying. SSD/HP was found to be the most suitable drying method for drying chicken as an ingredient for ready-to-eat noodle.     

Analysis of giant pumpkin (Cucurbita maxima) drying kinetics in various technologies of convective drying

The paper analyses the results of the research on drying a variety of giant pumpkin (Justynka – 957). The research involved drying kinetics of pumpkin as well as changes in the volume of 10 mm pumpkin cubes, dried at the temperature of 80 °C, using free (natural) convection and in the forced convection in the tunnel dryer, with the drying factor speed of 1.2 m s⁻¹ and in the fluid bed dryer. Drying kinetics of pumpkin pieces dried in the tunnel dryer, fluid bed dryer and during two-stage initial drying in the tunnel, and in the fluid bed dryer were examined. Measurements results were used to verify the theoretical models of drying kinetics of the first period taking volume shrinkage into consideration, and the second period of the examined processes.     

响应面法优化香菇柄变温压差膨化干燥工艺

为了对香菇柄变温压差膨化干燥工艺进行优化,采用响应面的中心组合设计方法,分析膨化温度（X₁）、抽空温度（X₂）和抽空时间（X₃）三个因素对产品含水率（Y₁）、色泽（Y₂）和膨化度（Y₃）的影响,根据实验数据推出描述三个指标的二次回归模型,并对变量进行响应面分析,得出优化膨化干燥工艺:膨化温度86℃,抽空温度69℃,抽空时间2 h。此条件下,膨化干燥的香菇柄的含水率为3.83%,色差值为42.29,膨化度为0.685。与热风干燥相比,变温压差膨化干燥产品膨化效果好,该技术可以应用于香菇柄的膨化产品。      

Effects of various pretreatments and drying methods on Salmonella resistance and physical properties of cabbage

The combined effects of pretreatment and drying methods on the resistance of Salmonella attached to vegetable surfaces as well as some physical properties, in terms of color and shrinkage, were investigated. Cabbage was used as a test vegetable and Salmonella Anatum was used as a test microorganism. Cabbage leaves were pretreated either by soaking in 0.5% (v/v) acetic acid for 5 min, blanching in hot water for 4 min or blanching with saturated steam for 2 min prior to either hot air drying, vacuum drying (10 kPa) or low-pressure superheated steam drying (10 kPa) at 60 °C. Based on an initial Salmonella contamination level of approximately 6.4 log CFU/g, soaking in acetic acid, hot-water and steam blanching resulted in 1.6, 3.8 and 3.6 log CFU/g reduction in the number of Salmonella, respectively. Drying without pretreatment could not completely eliminate Salmonella attached on the cabbage surfaces, while no Salmonella was detected on the pretreated samples at the end of the drying process. Volumetric shrinkage was not affected by the pretreatment and drying methods. Dried blanched samples exhibited greener and darker color than the dried acetic acid pretreated and untreated samples.