Drying characteristics of mango slices using the Refractance Window™ technique

Mango slices (1 and 2 mm thickness) were dried by using the Refractance Window™ (RW) technique with the water bath temperature set at 92 °C. Drying kinetics, water activity, and color change were determined and compared with those obtained by drying the slices in a tray dryer at 62 °C and an air velocity of 0.52 m/s. At 1 h, moisture contents of 0.013 (for 1 mm sample) and 0.048 (for 2 mm sample) kg water/kg dry solid for RW, and 0.966 (for 1 mm sample) and 3.614 (for 2 mm sample) kg water/kg dry solid for tray drying were obtained and water activity was less than 0.5 for RW and close to 0.97 for tray drying. The tray dryer took 4 h to reach results similar to those of RW at 1 h. The samples dried by RW exhibited diffusivities of 4.40 × 10⁻¹⁰ (for 1 mm sample) and 1.56 × 10⁻⁹ (for 2 mm sample) m²/s, which are larger than those exhibited by the air-dried samples, 2.08 × 10⁻¹¹ (for 1 mm sample) and 6.83 × 10⁻¹¹ (for 2 mm sample) m²/s.     

单液滴干燥过程中阿拉伯胶乳液的干燥特性

喷雾干燥塔是一个完全封闭的设施,难以对干燥过程中的液滴取样分析。本试验以阿拉伯胶包埋油脂的水包油(O/W)型乳液为样液,采用单液滴干燥技术(SDD)模拟喷雾干燥条件,通过分析乳液液滴在干燥过程中的形态收缩和干燥动力学参数的变化,探究干燥气流速度和乳液中固形物含量对颗粒的表面形成机制的影响。结果表明,在0.70,0.90,1.10 m/s 3种干燥气流速度下乳液液滴的干燥行为差异很大。在1.10 m/s的干燥气流速度下,液滴水分蒸发最快,表壳形成最早,最终所得颗粒收缩率最小。乳液总固形物含量对液滴干燥行为的影响也较为明显。随着总固形物含量的增高,乳液液滴水分蒸发越慢,表壳形成越早,最终所得干燥颗粒形态越大。本试验对于干燥动力学模型的研究和喷雾干燥产品品质的改善具有指导性意义。     

Drying kinetics and quality of beetroots dehydrated by combination of convective and vacuum-microwave methods

Beetroot cubes were dehydrated by convective drying in hot air at 60 °C and by the combination of convective pre-drying (CPD) until moisture content 1.6, 0.6 or 0.27 kg/kg db and vacuum-microwave finish drying (VMFD) at 240, 360 or 480 W. The control samples were obtained by freeze-drying (FD). The drying kinetics of beetroot cubes was described with an exponential function. VMFD significantly reduced the total time of drying and decreased drying shrinkage in comparison with convective method. A critical moisture content divided the temperature profile of samples during VMFD into increasing and falling periods. At the falling temperature period a significant increase in the colour parameters L^∗, a^∗ and b^∗ was found. VM treated samples as well as FD ones exhibited lower compressive strength, better rehydration potential and higher antioxidant activity than those dehydrated in convection. Increasing the microwave wattage and decreasing the time of CPD improved the quality of beetroot cubes dried by the combined method.     

固定床热风干燥模式对荔枝干制特性的影响

采用固定物料位置固定热端(模式I)、变换物料位置固定热端(模式II)和固定物料位置变换热端(模式III)三种模式对荔枝果实进行固定床热风多阶段干燥,分别测定了不同物料层(A、B和C三层)物料的热风风速、温度、水分含量、干燥速率、有效扩散系数(Deff)和体积收缩率。结果表明,不同的干燥层物料的热风和温度分布不均匀。经过四阶段共26 h干燥,模式I、II和III中整体样品的水分含量分别为45.70%、42.07%和41.18%。模式I中A层物料的终水分含量为28.44%,显著低于B层和C层样品(p<0.05),Deff为1.48×10-6m2/s,显著大于B层和C层物料(p<0.05)。模式II各层间物料终水分含量和Deff差异不显著(p>0.05),干燥较均匀。模式III中A层物料的终湿基含水量和Deff与B、C层的物料的相比差异不显著(p>0.05),干燥较均匀,可实现简约操作和规模加工。     

Shrinkage of Mirabelle Plum during Hot Air Drying as Influenced by Ultrasound-Assisted Osmotic Dehydration

Convective drying in hot air is still the most popular method applied to reduce the moisture content of fruits and vegetables. Conventional hot-air drying of Mirabelle plum is considered to be a slow and energy intensive process. This is due to the fact that the waxy skin of Mirabelle plum has low permeability to moisture, a fact which results in high shrinkage. The aim of this study was to investigate the effect of ultrasound-assisted osmotic dehydration pretreatment on shrinkage of Mirabelle plum as a function of moisture content with the end goal of optimizing operating conditions that minimize shrinkage of the produce during drying. Results showed that application of ultrasound-assisted osmotic dehydration led to a significant (p < 0.05) decrease in shrinkage (from 76.41 to 64.05%). A linear relation between moisture loss and shrinkage was observed. Results indicated that shrinkage may be easily estimated from changes in moisture content, and independent of the drying rate. Inversely, determination of shrinkage would provide an indirect indication of moisture content.     

Design of a forced-air-twin-chamber for investigating the effects of controlled levels of non-uniformity in heat treatment of tomatoes on product quality

A twin-chambered forced-air apparatus was built to simultaneously apply different environments to each hemisphere of tomato (Lycopersicon esculentum Merr.) fruit. This setup enabled one hemisphere of each fruit to be exposed to an air temperature–velocity combination of 39 °C/0.24 m s⁻¹; while the other hemisphere was simultaneously exposed to a combination of 36 °C/0.24 m s⁻¹, 37 °C/0.24 m s⁻¹, or 36 °C/0.12 m s⁻¹. Tomato fruits were divided into four lots: one left untreated; two lots were uniformly heat treated by maintaining the same environment in each chamber; and the remaining were subjected to twin chamber heat treatment. The fruits were then transferred to storage conditions at 14 °C, and allowed to ripen at 20 °C or subjected to chilling injury at 2 °C. The temperature difference between the two chambers significantly influenced the uniformity of color, whereas the firmness, titratable acidity and sugar to acid ratio were only marginally affected. Decreasing the temperature difference between the two chambers or increasing air velocity in heated chamber significantly improved the uniformity of quality.     

玉米薄层干燥特性对比试验研究

在热风薄层干燥试验平台上对玉米进行薄层干燥对比试验,采用单因素试验与正交试验相结合的方法,以玉米发芽率、裂纹率及干燥速率为指标,研究影响玉米干燥特性的主次因素,确定最优干燥工艺参数。试验结果表明:在玉米原始含水率不变的情况下,热风温度的影响最为显著。     

yankee烘缸与高温热风气罩结合用于纸幅干燥节约能量、提高质量和增加产量

该文论述新颖热风气罩与传统yankee烘缸,联合使用于生活用纸纸幅干燥取得很好效果,在提高热风温度25%～30%的情况下使过程的干燥速率加快30%～50%。运种新颖热风气罩是在老式平台的基础上对其结构设计和材料强度进行优化和改进而成,从而能突破传统干燥过程里空气受到温度限制,从而在作业过程里实现节约能量、提高质量和增加产量。     

热风风速和相对湿度对扇贝柱干燥特性及品质的影响

本试验以海湾扇贝柱为原材料,进行薄层干燥试验,研究恒定风温下不同热风风速、相对湿度对产品干燥特性和品质的影响。测定干燥过程中水分含量和水分活度（Aw）的变化,并对所得产品的收缩率、复水率、色泽、质构等品质特性进行了比较分析。结果表明, 整个干燥过程均处于降速干燥阶段,起始阶段干燥速率下降最快,随着干燥时间的延长,干燥速率逐渐平缓。提高风速、降低热风相对湿度都可以显著缩短干燥时间,水分活度（Aw）下降速也越快。不同热风风速和相对湿度对干贝的质构特性、收缩率和复水率也有显著影响,但是对干贝色泽影响并不显著。综合考量干燥速率和干制品品质,选择热风风速为0.8~1.2 m/s、热风相对湿度在8%左右为较适宜的海湾扇贝柱热风干燥条件。     

Modeling Effective Moisture Diffusivity of Wheat (Tajan) During Air Drying

Drying conditions can greatly affect the physical and mechanical properties of grains. The drying process must be controlled to reduce or minimize drying damage. In this paper the thin layer drying behavior of wheat (Tajan) in a convective dryer is experimentally investigated. The mathematical modeling by using thin layer kinetics drying models available in literature was performed. Drying experiments were conducted at inlet drying air temperatures of 35, 45, 50, 60 and 70°C and at a fixed drying air velocity of 0.3 m/s and initial moisture content of 0.26–0.27 (d.b.). The effects of drying air temperature on the model's parameters were predicted by a linear regression analysis. The constants and coefficients of this model were be explained in terms of drying air temperature. A correlation coefficient (r) of 0.99 was found for the multiple regression model of moisture content during the drying process using different temperature values. Values of the diffusion coefficients for the whole kernel ranged from 2.28 × 10^?11 to 1.14 × 10^?10 m²/s.     

Drying of yellow pea starch on inert carriers: Drying kinetics,moisture diffusivity,and product quality

This study aimed at investigating the drying of yellow pea starch dispersions on inert solid carriers and determining the drying kinetics, moisture diffusivity and the product quality, quantified through damage index and final moisture content. Drying kinetics accomplished in a convective drying tunnel show that the overall mass transfer is controlled by internal migration of moisture within the starch particles. For a given inlet air temperature from 100 to 180 °C, the apparent diffusion coefficient derived from the drying curves increases exponentially with the instantaneous moisture content, with values ranging from 4 × 10⁻¹¹ to 3 × 10⁻⁸ m²/s. Due to low diffusivity and the thin coat formed on the surface of solid carriers, the resistance to internal diffusion is negligible as compared to the overall mass transfer resistance when drying of starch dispersions takes place on inert solid carriers. Drying of yellow pea starch dispersion on Teflon particles as inert carriers was studied in laboratory and pilot fast spouted bed dryer for inlet air temperatures from 140 to 240 °C, and initial solid content of 38%, mass (d.b.). The starch damage index for targeted product moisture content was below 2.5% in the inlet air temperature range from 120 to 210 °C, when atomizing from the bottom of dryer.     

Shrinkage,porosity and density behaviour during convective drying of spirulina

Spirulina (Arthrospira platensis) is a microalgae produced for its nutritional and therapeutic qualities. Drying is the main process of conservation used for this product and it is so essential to control its drying parameters. In this study, shrinkage, porosity and density of spirulina cylinders during convective drying were investigated. For 3, 4 and 6 mm diameter cylinders, results showed a weak and anisotropic shrinkage. The glass nature of the product during the drying process tended to reduce its shrinkage and to facilitate formation of pores and cracks. The product had a final porosity approaching 80% and most of its evaporated water during drying was replaced by gas. The apparent density strongly varied during drying. Its value decreased from 850 kg/m³ at the beginning of the drying to about 300 kg/m³ at the end of the drying. The effective water diffusivity was influenced by shrinkage. Its value was over-estimated about 36.48% to 92.41% when shrinkage was not considered in data processing.     

Characterization and CFD modelling of air temperature and velocity profiles in an industrial biscuit baking tunnel oven

The industrial baking of cereal products is commonly performed in tunnel ovens, which give operators high flexibility for adjusting baking conditions to optimum values. This paper discusses the application of a CFD approach to predict the air temperature and velocity profiles inside the baking chamber of an industrial indirect gas-fired tunnel oven used for biscuit baking. We used two three-dimensional CFD models (one not covering the conveying band of biscuits and the other including it) to describe the complex air circulation resulting from the mechanisms of air input and exit at the ends of the oven and of air extraction through the different extraction points located along the oven length. Comparison of numerical results with experimental measurements shows a fairly close agreement in the qualitative prediction and a few inaccuracies in the quantitative prediction of the air temperature profiles within the baking chamber. Furthermore, the comparison also reveals great differences in the air velocity profiles.     

竹笋热风薄层干燥特性及动力学分析

干燥是竹笋加工中最为常见的一种方式,为了解竹笋在热风薄层干燥条件下的干燥特性,本实验以大叶麻竹笋为试验原料,竹笋片干基含水率和干燥速率为试验测试指标,研究了不同干燥温度、风速和笋片厚度等因素对干燥速率的影响,并建立竹笋热风薄层干燥的动力学模型。结果表明:热风薄层干燥温度、风速和笋片厚度均对竹笋的干燥特性影响较大。随着干燥温度和风速的升高,干燥速率增加;随着笋片厚度的增加,干燥速率降低。不同条件下的干燥均可分为加速、恒速和降速干燥3个阶段。竹笋的适宜热风薄层干燥条件为干燥温度80℃、风速2.0 m/s、笋片厚度1.0 cm。竹笋热风薄层干燥的动力学满足Page模型,Page模型适合对竹笋热风薄层干燥过程进行描述和预测。所得研究结果将为竹笋干的热风薄层干燥可控制工业化生产提供参考。     

蓝靛果果粉喷雾干燥工艺优化及其品质

为优化喷雾干燥制备蓝靛果果粉的工艺参数,以蓝靛果为原料,通过单因素和正交试验分析,确定蓝靛果果粉喷雾干燥的最佳工艺条件,并对比分析喷雾干燥和真空冷冻干燥所得果粉营养成分及物理特性的差异,评价喷雾干燥对蓝靛果果粉品质的影响。结果表明:喷雾干燥的最佳工艺条件为料液比1∶4(g/mL)、麦芽糊精添加量15%、进风温度155℃、进样速度8.4 mL/min、进风量26 m³/h,在该条件下,蓝靛果果粉的得率为(32.19±0.13)%。喷雾干燥所得果粉花色苷含量为(4.18±0.31)mg/g,V_C含量为(0.42±0.05)mg/g,总酚含量为(45.32±0.49)mg/g,比真空冷冻干燥分别减少了28.55%,33.33%和24.98%,但喷雾干燥所得果粉具有良好的物理特性,水分含量少,粒度小,溶解性和流动性均优于真空冷冻干燥,适宜在蓝靛果果粉加工产业中推广应用。     

Effect of Temperature on Salt Diffusion into Vegetable Tissue

The diffusion process has many applications in food processing operations, such as extraction; preservation (curing, salting, and smoking); drying; and color transfer. Our main objective was to measure the diffusion coefficient, D_s, of salt into vegetable tissue (celery, mushroom, and water chestnut) as a function of temperature. For this purpose, a sample of tissue was used to separate donor and receiver compartments, each with solutions of different salt concentrations. Values of D_s were determined by periodic monitoring. The results show that the equilibrium distribution coefficient, K, and D_s of all materials were significantly affected by temperature (p < 0.05). The temperature dependence of D_s for all three materials was described by the Arrhenius equation, with water chestnut showing the lowest activation energy.     

玉米薄层变温干燥特性及工艺参数优化研究

为提高玉米的干燥品质,降低干燥能耗,在前人研究谷物变温干燥的基础上,探究变温干燥工艺对玉米干燥特性及品质的影响。分析初始干燥温度(45～70℃),转换温度含水率(18～26%)、升温幅度(5～25℃)、缓苏比(1:1;2:1;3:1;4:1;5:1)等试验因素对玉米干燥速率及外观品质(裂纹率增值、色差)的影响规律;采取多元二次回归正交旋转组合试验方法,以初始干燥温度、转换温度含水率、升温幅度及缓苏比为试验因素,以裂纹率增值和色差值为目标响应值,通过建立回归模型和响应面图,分析玉米变温干燥特性并阐明产生结果的原因。通过单因素分析,结果表明：初始干燥温度为45～55℃、转换温度含水率为20～24%、升温幅度为5～15℃、缓苏比为2:1～4:1条件下可获得较好的干燥品质;变温干燥的最佳工艺参数组合为初始温度为50.59℃、转换温度含水率为21.56%、升温幅度为5℃、缓苏比为3.8:1,干燥后的玉米裂纹率增值为10.00%、色差值为2.056,实验值与预测值之间的相对误差为4.25% ,研究结果可为玉米变温干燥的技术改进及深入探讨变温干燥工艺对玉米品质变化机理研究提供数值和理论参考。     

食品冷冻干燥速率分析

针对食品冷冻干燥过程中,存在过程速率慢,生产周期长的问题,对影响食品冷冻干燥的传热传质速率的诸因素从理论上进行了综述、分析,为食品冷冻干燥技术的进一步研究、应用提供一定的参考。     

Modeling Shrinkage and Density Changes During Microwave-Vacuum Drying of Button Mushroom

Shrinkage characteristics and apparent density of whole button mushrooms were determined at various moisture content levels (ranging from 5 to 92% wet basis) during microwave-vacuum drying at two different power (150 and 250 W) and pressure (10 and 20 kPa) levels. The above properties during convective hot air drying at 60°C were also measured for comparison. In both microwave-vacuum and air-drying methods, the shrinkage (volumetric and diametric) of mushroom showed a linear behavior with moisture content. Experimental data showed that the effect of the system pressure on shrinkage and density was more significant than the power level during microwave-vacuum drying. Moisture content and method of drying also affected shrinkage statistically. Microwave vacuum drying produced less shrinkage than air drying. Simple mathematical models were used to correlate the above properties with the material moisture content. The models were fitted to experimental data satisfactorily, and the parameters were estimated.