Experimental study on drying of pear slices in a convective dryer

The experiments were conducted on pear slices with thickness of 5 mm at temperatures of 50, 57, 64 and 71 °C with an air velocity of 2.0 m s^?1. Prior to drying, pear slices were pretreated with citric acid solution (0.5% w/w, 1 min, 20 °C) or blanched in hot water (1 min, 85 °C). Also, the untreated samples were dried as control. The shortest drying time of pear slices was obtained with pretreatment with citric acid solution. It was observed that whole drying process of pear slices took place in a falling rate period. Four mathematical models were tested to fit drying data of pear slices. According to the statistical criteria (R², χ² and RMSE), the Midilli et al. model was found to be the best model to describe the drying behaviour of pear slices. The effective diffusivity of moisture transfer during drying process varied between 8.56 × 10^?11 and 2.25 × 10^?10 m² s^?1, while the activation energy of moisture diffusion in pear slices was found to be 34.95–41.00 kJ mol^?1.     

直触式超声强化热风干燥梨片的干燥特性

为探讨直触式超声强化热风干燥梨片的干燥特性,进行梨片超声强化热风干燥试验,研究超声功率及热风温度对梨片干燥过程及产品品质的影响规律。结果表明:提高热风温度及直触式超声功率能够明显缩短干燥时间,较低温度下的超声强化效果要好于较高温度下的。BP神经网络模型能较好地预测梨片超声强化热风干燥过程中的水分变化规律。超声产生的空化效应和机械效应可增大水分流动性及提高梨片的复水率,且有利于保留梨片营养成分,但干燥温度过高则不利于总酚、总黄酮、VC等热敏性营养成分的保留。梨片超声强化热风干燥过程的层次分析法优化结果表明,最优干燥参数为热风温度35℃、超声功率48 W,此时梨片总酚含量为408.88 mg/100g,总黄酮含量为157.94mg/100g,VC含量为42.36mg/100g,复水率为3.32。因此,将直触式超声强化技术用于梨片热风干燥中,能够显著缩短干燥时间、明显提高梨片干燥品质。     

Mathematical modelling of hot air drying of sweet potato slices

The effect of air dry bulb temperature, air relative humidity, air velocity and sample thickness on the thin-layer air drying of sweet potato slices was investigated. The drying rate curves consisted of two approximately linear falling rate periods and contained no constant rate period. Several mathematical models were fitted to the drying rates of sweet potato slices under a range of drying conditions. It was found that the modified Page equation best described the thin-layer air drying of sweet potato slices down to a moisture content of 10% dry basis. Correlations were also determined for the slope and intercept of the modified Page equation in terms of the experimental variables.     

The glass transition approach to determination of drying protocols for colour stability in dehydrated pear slices

Colour stability in dehydrated fruit is often attained by use of sulphite treatment to inhibit browning during processing and storage. However, colour stability may be able to be conferred on products by ensuring that the molecular mobility is restricted in dried fruit by drying to sufficiently low moisture to raise the glass transition temperature (under mild conditions). Pear slices were dehydrated at a low temperature (40 °C) to a low final moisture content (below 5%) after it was shown that, for a moisture content of 22% (which is the moisture content of commercial dehydrated pears) pretreatment with sulphite would be necessary to stabilise the colour. The use of longer drying regimes resulted in a moisture content where the food matrix would be closer to the glassy state and conferred colour stability on the dehydrated product compared to a product containing more moisture. For these low‐moisture products, pretreatment with sulphite would not be necessary to preserve colour stability.     

梨片酶褐变控制方法的研究

探讨了抗坏血酸在不同温度、时间和浓度条件下,对梨片多酚氧化酶的抑制效果。实验表明,该酶活性在1%～1.5%的抗坏血酸溶液中显著降低。1%抗坏血酸溶液在pH1或pH2的条件下,能显著抑制酶活性;在60～70℃范围内15min能明显降低酶褐变,延长浸泡时间也能控制酶褐变。     

Experimental investigation and theoretical modelling of absolute convective drying of starch

Starch is a granular, hygroscopic, capillary-porous material with an intricate structure. It is known that drying starch till 0% moisture is a physical treatment that modifies starch properties. However, depending upon the heat and mass transfer mechanisms prevalent in the drying system, starch properties are modified in a unique manner. Therefore, the drying operation itself needs to be thoroughly understood. Potato starch was treated in an oven at three high-temperature levels (110, 130 and 140 °C) and for three sample thicknesses (2.8, 5.6 and 11.2 mm). It was observed that drying of starch with moisture content in the hygroscopic range occurred only in the 2nd falling rate period. Two existing theoretical, drying models, one based upon the Krischer Theory and the other based upon the Percolation Approach, were considered apt for modelling the oven drying. Both models describe the experimentally measured moisture profiles well. During drying, transition from one water sub-population to another was smooth. The effective diffusion coefficient decreased with moisture content and increased with temperature, but did not follow Arrhenius’ Law above 130 °C.     

Kinetics of drying apple slices

The process of drying apple tissue under most conditions may be divided into two main periods viz primary and secondary falling-rate periods. For most drying conditions the secondary falling-rate period is longer and has the greater influence on the overall rate. When the drying capacity of the air is very low an initial constant-rate period may occur. The drying rate constant varies with temperature with an Arrhenius-type relationship and the available evidence suggests that temperature-induced changes in the rate may be caused by vapor pressure changes Air velocity and relative humidity have their greatest influence in the early part of the drying process Towards the end of drying, internal resistance to water movement becomes rate-controlling, and external factors have little influence. An explanation of the observed drying characteristics of apple tissue in terms of the diffusion of water vapour through a ‘skin’ of dried cells is suggested.     

Infrared drying of button mushroom slices

The effect of different infrared power levels on the drying kinetics of button mushrooms was investigated. Mushroom slices were dried at infrared power levels of 83, 125, 167, and 209 W. The power level affected the drying and rehydration characteristics of mushroom slices. Drying time was reduced from 300 min to 40 min as the infrared power level increased from 83 to 209W. Mathematical models frequently used to represent drying of agricultural products were fitted to experimental data of mushroom drying. The parabolic model was the best for representation of mushroom drying. Effective moisture diffusivity varied from 3.81×10^?10 to 4.20×10^?9 m²/s over the infrared power levels used. The activation energy was estimated using a modified Arrhenius-type equation and calculated to be 7.55 kW/kg.     

红外辐射干燥胡萝卜的试验研究

采用红外辐射干燥的方法,对胡萝卜片进行了不同条件下的干燥试验,研究红外辐射干燥法对不同干燥参数条件下胡萝卜片的含水率及颜色变化,结果表明物料的厚度、加热温度对干燥含水率变化影响较大,而物料的厚度、加热温度和辐照距离对胡萝卜片的颜色变化均很大。在胡萝卜片厚度为4.5mm,辐照距离为12cm,物料温度55℃时,在保证干燥品质较好的条件下,效率最高。     

热风干燥蘑菇片的工艺研究

目前脱水蘑菇片脱水工艺中的产品质量指标衡量多为感官的实验所确定,且侧重于某种工艺条件对产品的质量影响。本文以复水率、水分含量、色泽、蛋白质含量、灰分含量作为衡量指标,采用正交实验对蘑菇片热风干燥的各项工艺条件(护色剂的选择,预煮时间的选择,前期干燥时间,后期干燥时间)分别进行优化,得到综合最优工艺为0.3％NaSO3与柠檬酸混合作为护色剂,不经预煮,前期干燥(35℃)2h,后期干燥(55℃)11h。     

枣片真空干燥方式的比较研究

以木枣为原料,采用真空冷冻和真空低温2种干燥方式加工枣片,探讨比较了2种方式加工的枣片的Vc含量、复水率、褐变度,并且对枣片进行了综合的感官评价。研究表明,真空冷冻干燥的枣片在Vc、褐变度、复水率方面优于真空低温干燥,但冷冻干燥的时间长,成本高。两种真空干燥方式得到的枣片综合评价得分相同,冷冻干燥的枣片色泽、外观、气味均好于低温干燥,但酥脆度较差,口感不如真空低温干燥的枣片。     

Effects of air-impingement jet drying on drying kinetics and quality retention of tomato slices

Food Science and Biotechnology - The purpose was to explore the drying kinetics, the moisture effective diffusivities, color, total polyphenols, lycopene and antioxidant activities of dried tomato...     

Experimental investigation of drying behaviour and conditions of pumpkin slices via a cyclone‐type dryer

This paper describes an experimental investigation of the drying behaviour and conditions of pumpkin slices via a convective cyclone‐type dryer. Drying experiments were conducted at air inlet temperatures of 60, 70 and 80 °C and air velocities of 1 and 1.5 m s^?1. Samples of 200 g of cylindrical pumpkin slices (thickness 5 mm × diameter 35 mm) were arranged in a single layer on each of two trays. The least squares method was applied to derive the drying curve equation of samples. During the experiments the following parameters were measured: weight loss, temperature, relative moisture and velocity. From these parameters, dimensionless mass loss, moisture content, mass shrinkage and drying rate of samples were calculated and are discussed in detail. Additionally, the transport of water during dehydration was described by the diffusion mechanism, and Fick's equation was used for evaluation of the experimental data. The linear sections of drying curves were analysed by linear regression to obtain the moisture diffusivities. It was found that pumpkin slices would dry perfectly within 340–720 min under these drying conditions. The convective cyclone dryer could also be used to dry other products. Thus it is expected that this new dryer will help farmers and producers to reduce the cost of drying. Copyright © 2003 Society of Chemical Industry     

微波气流预干燥和微波真空组合干燥生产甜瓜片

研究了微波气流预干燥(MAD)和微波真空(MVD)组合干燥甜瓜片,表明这是一种有潜力的干燥方法。样品先通过微波气流干燥脱去一些自由水,然后通过微波真空干燥到最终水分含量低于7%(湿基)。甜瓜片利用微波气流(MAD)和微波真空(MVD)组合干燥后测得Vc保留率和物性(收缩率,色差,质地和复水率)然后同冷冻干燥(FD)、微波气流干燥(MAD)、气流干燥(AD)和常规热风干燥(HAD)分别进行比较,表明,MA+MVD方法干燥的甜瓜片的Vc保留率接近冻干的甜瓜片,大大优于传统的热风干燥。当前方法干燥的样品表现出的复水率、色差、质构与冻干的产品非常相似,但是出现了明显的膨化现象,然而,这正是生产果蔬脆片所期望得到的结果。     

Experimental investigation of jet drying of birch and spruce veneers and modelling with a simplified approach

The paper presents experimental results of jet drying tests of birch ( Betula pendula) and spruce ( Picea abies) veneers at temperatures of 140°C and 190°C. Results include drying rates for 1.5 mm thick birch veneers as well as 1.5 mm and 2.6 mm thick spruce veneers of both heartwood and sapwood. Based on the test results, material parameter values for a simplified drying model are assessed. The model is based on the use of an effective diffusion coefficient and an effective surface emission coefficient, which values are calibrated to fit to the experimental results. It is observed, that separate model parameter sets are needed for the two different species but also for occurrence of heartwood or sapwood (spruce) and different thickness values of veneers.     

热泵干燥温度对柿子片干燥特性及品质的影响

目的:探明热泵干燥温度对柿子片干燥特性和品质的影响。方法:以柿子为原料,研究干燥温度对柿子片干燥时间、干燥速率,以及干制品色泽、硬度、复水率、单宁、总糖、维生素C和总酸的影响。结果:当热泵干燥温度为65℃时,柿子片干燥速度快,干燥时间短,此时干燥产品色泽鲜艳,与鲜果色泽相近,复水性能好,硬度最低,口感最好,总酸和维生素C含量最高,总糖等营养成分含量适中。结论:柿子片的最适热泵干燥温度为65℃。     

芒果切片热风干燥特性及模型

目的：为对芒果热风干燥过程进行预测与控制。方法：以新鲜金煌芒为试验材料,研究热风温度（60,65,70 ℃）和芒果切片厚度（0.8,1.0,1.2 cm）对芒果热风干燥曲线、干燥特性曲线、水分有效扩散系数等的影响,并选取常用的适用于果蔬的6种干燥模型进行拟合、分析及验证,选出最适合芒果热风干燥的模型。结果：随温度的升高,切片厚度的减小,加快了芒果片的干燥速率,所需的干燥时间越短。水分有效扩散系数随温度和厚度的增大而增大,为1.401 39×10^-10～3.655 46×10^-10 m²/s。Logarithmic模型的R²最大、X²和RMSE最小,分别为0.998 87,0.000 124 779,0.001 37。结论：Logarithmic模型预测值与试验值验证基本吻合,可以较好反映芒果片在干燥过程中水分含量的变化规律。     

哈密瓜切片热风干燥特性及数学模型

目的:提高规模化生产的哈密瓜品质,缩短干燥周期。方法:以不同漂烫时间(0.5,1.0,1.5,2.0,2.5 min)、浸渍液(0.1%,0.2%,0.3%,0.4%,0.5%柠檬酸溶液)预处理哈密瓜切片,并分别研究不同热风温度(35,45,55,65,75℃)、热风速度(0.5,1.0,1.5,2.0,2.5 m/s)和切片厚度(2,4,6,8,10 mm)条件下的哈密瓜切片热风干燥特性和水分扩散系数,拟合不同薄层干燥数学模型。结果:0.4%柠檬酸预处理后得到品质最优的干制产品,热风温度和切片厚度对切片干燥影响较为显著,哈密瓜切片无恒速干燥阶段,有效水分扩散系数为1.1348×10^-7~4.9080×10^-7 m²/s,活化能为28.15 kJ/mol。结论:哈密瓜切片的最佳热风干燥工艺为热风温度55℃、热风速度2.0 m/s、切片厚度6 mm,Page模型具有最高的R²值和最小的均方根误差,更适于评估和预测哈密瓜热风干燥的水分去除规律。