无花果热风干燥过程中水分变化及其品质研究

为探究不同温度热风干燥过程中水分含量变化情况及对无花果品质的影响,该研究采用不同温度热风干燥（50、60、70、80℃）对无花果进行干燥处理后,运用低场核磁共振（low-field nuclear magnetic resonance,LF-NMR）技术检测各温度干燥过程中无花果的水分迁移规律,采用色差计测定不同干燥温度的无花果色泽变化,并对其总酚含量及抗氧化活性进行考察。结果表明,随干燥温度的升高,无花果的干燥速率显著提高,达到平衡的时间明显缩短。低场核磁共振信号显示,随干燥时间的延长,核磁共振横向弛豫T2峰向左移动,说明随着干燥时间的延长无花果中水分自由度降低。T2峰横向弛豫时间、峰面积（A）与水分比相关性分析结果显示,干燥过程中无花果的水分比（moisture ratio,MR）与T21、T23的横向弛豫时间以及A23、A总呈显著相关。低场核磁共振成像（low-field magnetic resonance imaging,LF-MRI）图谱显示,新鲜无花果内部水分分布较为均匀,随干燥时间的延长,水分由内向外周扩散。不同温度烘干样品的品质分析显示低温烘干（50℃或60℃）能更好地保持无花果的色泽,而高温烘干（80℃）样品中多酚类成分含量最高,其抗氧化活性最好。以上研究表明低场核磁共振技术可用于热风干燥过程中无花果水分含量、分布及其状态变化的无损检测。     

酸辣猪肉干热风干燥动力学及其品质研究

以猪后腿肉为原料,研究酸辣猪肉在不同热风温度(50,65,80,95℃)、不同热风速率(1,2,3,4 m/s)下的干燥曲线和干燥速率曲线,对干燥过程中水分比与干燥时间的关系进行回归拟合以构建干燥动力学模型,并探讨不同热风温度和风速对酸辣猪肉干品质的影响.研究表明,酸辣猪肉干干燥过程分为降速和恒速两阶段,且干燥时间与干...     

谷物干燥及风能利用

目前,先进国家用烘干机干燥谷物已基本普及,且烘干机种类很多。而国内,由于经济和技术等原因,烘干机总是迟迟不能推广,尤其是近几年来“能源危机”的影响,尽管有许多科技工作者想了许多办法,力求干燥机械化、成本降低,但效果并不显著。     

红外辐射在谷物干燥中的应用

阐述了红外辐射干燥的基本原理,分析了红外辐射在谷物干燥中的应用形式,提出了今后的研究方向.     

紫苏智能排湿干燥过程的干燥动力学及品质变化规律研究

为了明确紫苏采后干燥处理时的特性,本文利用可智能排湿的烘干装置研究了紫苏茎叶在不同温度条件下的干燥特性及品质变化;给出了紫苏茎叶在50~80 ℃的温度区间内干燥时的干基含水率变化及干燥速率曲线,并用数学模型对干燥数据进行拟合;对比了不同温度烘干紫苏及冻干、自然阴干紫苏间的品质差异,包括挥发油含量、迷迭香酸含量、总黄酮及总酚含量及抗氧化能力等指标;利用超快速气相电子鼻分析系统分析了挥发性风味物质的变化,基于以上指标综合评判不同干燥方式紫苏的品质差异。结果表明,紫苏叶的干燥过程始终处于降速干燥阶段,而紫苏茎经历提速、恒速及降速三个干燥阶段,紫苏茎、叶分别适用于Page模型及Two-term模型。智能排湿的低温烘干（50 ℃）与传统的阴干处理相比,在活性成分含量、抗氧化性能及气味物质含量及丰度上均无较大差异,挥发油等物质含量表现更优。干燥温度是影响紫苏品质的一个重要因素,紫苏的活性成分含量、抗氧化能力及风味物质含量均会随温度的提高而出现不同程度的降低。     

谷物干燥方法的研究

介绍了谷物的各种干燥技术和方法,以及干燥方法的研究进展。目前谷物干燥方法主要有微波干燥、红外线辐射干燥、顺溜干燥、流化床干燥、低温真空干燥、热风干燥和喷动床干燥。     

谷物横流干燥数学模型研究进展

综述了国外有关谷物横流干燥数学模型的研究进展.谷物干燥过程具有非线、大时滞,难于控制等特点,横流干燥是目前应用较为广泛的谷物干燥的形式之一,干燥过程数学模型是谷物干燥机具设计、干燥作业自动控制以及干燥工艺优化的重要依据.阐述适用于谷物横流干燥的偏微分方程PDE模型、DP过程模型和随机模型的具体建模过程.     

干湿谷物混合干燥工艺与机理研究及高效节能谷物干燥机开发

文中对干湿谷物混合干燥工艺与传统干燥工艺的性能进行了试验对比,通过比化处理找出了干湿谷物混合干燥的最佳干燥参数。介绍了研制与开发的高效、节能谷物烘干机(5HGS)系列产品并介绍了两种烘干工艺的烘后粮食安全储粮试验等。     

温室主动型太阳能谷物干燥过程的数学模拟

通过谷物干燥过程各相关参数对谷物含水量的影响分析,用计算机模拟建立了以薄层干燥方程为基础的深床谷物干燥模型,并通过质平衡方程、热平衡方程、热传递方程和干燥速度方程得出谷粒水分（M）、谷粒温度（θ）、通过谷层后热空气温度（T）和热空气湿含量（H）,为温室主动型太阳能谷物干燥房设计提供了一定的参考依据。     

粤式杏仁饼干燥动力学及其品质变化

为建立粤式杏仁饼合理的焙烤工艺,以洞道干燥设备模拟工业化隧道式烤炉的焙烤环境,选择热风温度分别为80、100、120和140℃,将杏仁饼热风干燥曲线与基于薄层干燥模型的干燥曲线进行拟合,同时探究杏仁饼焙烤过程的品质变化。研究结果表明:所有杏仁饼的干燥过程都处于降速阶段。水分有效扩散系数D_(eff)介于8.32×10~(-9)~2.496×10~(-8)m~2/s,随着温度升高而升高。不同热风温度下的D_(eff)存在显著差异(P0.05)。采用6种薄层干燥模型进行了数据拟合,确定Page方程为优选干燥模型(平均R~2=0.997)。成品品质分析表明,120℃和140℃干燥的杏仁饼硬度没有显著差异(P0.05),但与80℃和100℃下干燥的杏仁饼硬度差异显著(P0.05);80℃干燥前后咀嚼性没有明显变化(P0.05),而100~140℃则会显著提高咀嚼性(P0.05)。不同干燥温度下杏仁饼的内聚性、色泽都有显著差异(P0.05)。从感官评价结果来看,120℃下干燥品质较好。对于低水分含量的杏仁饼而言,其内部为多孔结构,并非提高温度就能缩短干燥时间。在工业化生产过程中,应该从节能、水分迁移的速度和方向、杏仁饼的品质变化等方面综合考量进行烘焙条件的选择。     

Kinetics of colour change of bamboo shoot slices during microwave drying

The effect of microwave power on colour change kinetics of bamboo shoot slices was investigated during microwave drying. Colour changes were quantified by tri‐stimulus Hunter L (whiteness/darkness), a (redness/greenness), and b (yellowness/blueness) system. These values were also used for calculation of total colour change (ΔE), chroma, hue angle, and browning index (BI). Microwave drying as expected changed colour parameters because of browning. The values of L and b decreased, while values of a and ΔE increased during drying. Mathematical modelling of colour change kinetics indicated that L, b, chroma and BI could be defined using a first‐order kinetic model, while a, ΔE and hue angle could be defined using a zero‐order kinetic model. Considering together colour deterioration and quality of dried bamboo shoot slices at higher power reveals the need of process standardisation for getting good quality product.     

热风干燥过程中小白杏色泽的变化及其动力学研究

为降低小白杏因干燥引起的褐变,保证产品干燥后色泽良好,同时为小白杏干燥设备选型及工艺确定提供理论依据,选择热风干燥的方式,以新疆小白杏为原料,以亮度值(L)、红绿值(a)、黄蓝值(b)、总色差(△E)和褐变指数(BI)为考察指标,研究了热风干燥温度(40,50,60℃)和风速(2,3,4m/s)对新疆小白杏色泽的影响,并在该基础上建立新疆小白杏热风干燥色泽变化动力学模型,有效预测、调节杏褐变程度。结果表明:小白杏在不同风速、不同干燥温度条件下均发生了较为明显的颜色变化,不同热风干燥温度对干燥时间和干燥后杏干色泽均有显著影响,而不同干燥风速对干燥后杏干色泽影响不显著。在不同热风干燥温度和不同风速条件下干燥小白杏的L值和b值随着干燥时间的延长逐渐降低,而a值、△E值和BI值均逐渐升高。小白杏热风干燥过程中颜色参数的反应速率常数k值随着干燥温度的升高而呈现出一定的规律性变化,其中k值受热风温度的影响较大,受风速的影响较小。根据拟合决定系数R2的比较结果,通过动力学方程模拟,得出0阶模型能更好地描述和预测不同风速和不同干燥温度条件下小白杏在热风干燥过程中的颜色变化,而在不同风速和干燥温度条件下小白杏褐变动力学模型模拟效果较好的是1阶模型。该研究为小白杏干燥工艺及杏干产品感官品质控制提供了理论依据。     

美国红鱼贮藏过程中品质变化动力学模型研究

研究不同贮藏温度下美国红鱼的细菌总数、挥发性盐基氮(T-VBN)值及巯基含量随存放时间的变化规律及其动力学特性,建立细菌总数、挥发性盐基氮(T-VBN)值、巯基含量与贮藏温度和贮藏时间的动力学模型,以预测和控制养殖的美国红鱼在贮藏过程中的品质变化和货架期。贮藏过程中美国红鱼鱼肉的细菌总数增加,随贮藏温度的上升,鱼丸品质劣化速度加快。细菌总数、巯基和TVB-N值对一级化学反应模型和Arrhenius方程具有很高的拟和精度。     

Color change of selected vegetables during convective air drying

Abstract

Color changes of potato, carrot and pumpkin during air drying were the subject of this study. Air convective drying was done at 70°C and 1.5 m/s. Color of the material undergoing drying was measured with chromameter and expressed in the CIE system with chromaticity coordinates x and y, and luminance Y. It has been found that drying affects color of investigated vegetables. Luminance increased and chromaticity coordinates moved toward whiteness until a specific water content was reached. Thereafter, luminance decreased and x and y coordinates moved toward the color of the raw material. It is suggested that changes of color of drying materials were due to removal of water, substitution of water by air and deformation of surface (shrinkage). At the end of drying a concentration effect seems to predominate. Rehydrated material had a different color than that of raw one. The difference was depended on the kind of material investigated and its reconstitution properties. Nevertheless the color changes irreversibly due to the changes of surface and internal structure of the material caused by drying and rehydration processes.     

Kinetics of quality changes during food frying

This paper deals with kinetics of quality changes during food frying. The quality parameters of interests include color, texture, viscoelastic properties, volume/density, and nutraceuticals (Omega 3 fatty acids). The kinetic theory and determination methodology under isothermal/non-isothermal conditions are also reviewed. This paper presents the reported reaction rate constant, order of reaction, and activation energy for specific quality changes including phenomenological observations and important speculations. The changes of color, textural, and viscoelastic properties generally followed a first order reaction. In some studies, activation energy analysis could have been improved by applying corresponding system temperatures for the quality change reactions of interest. The kinetic information on volume/density changes and thermal degradation of nutraceutical is still limited to experimental observations of the changes.     

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.     

Colour change and weight loss of apple slices during drying

Drying of apple slices was studied in a conventional tray drier (initial slice thickness=0.3–1.0 cm, drier temperature=60–100 °C) and in a computer-controlled tunnel drier (initial slice thickness=0.8 cm, air tempera ture=50–100 °C, air flow rate=2.4 m/s). In most of the experiments the drying behaviour was characterized by a constant rate period, followed by a falling rate period. The constant rate drying period did not occur, and the colour of the dried slices was improved substantially with tunnel drying under computer control, when a linearly decreasing temperature profile from 100 °C to 70 °C was used. The quality improvement may be attributed partly ot the elimination of the continuous water film covering the surface in the constant rate drying period, which may serve as a medium for the reaction and transport of the chemical species.

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Farbveränderungen und Gewichtsverluste von Apfelstücken während des Trocknens

Zusammenfassung Apfelscheiben (0,3–1,0 cm) wurden in einem konventionellen Hordentrockner (60 bis 100 °C) und einem rechnerkontrollierten Tunneltrockner (Scheiben 0,8 cm, Lufttemperatur 50 bis 100 °C, Luftfluß 2,4 m · s^–1) getrocknet. Bei den meisten Experimenten wurde eine zweiphasige Trocknung beobachtet. Eine regelmäßige Trocknung fand dagegen bei einem gesteuerten, linearen Temperaturgradienten von 100 zu 70 °C statt. Dies verbesserte die Qualität der Produkte, offensichtlich wegen des Vermeidens einer Wasserfilm-Bildung auf den Oberflächen der Apfelstücke während des Trocknens. Ein derartiger Film kann ein Medium für Reaktionen und den Transport von Reaktanden Scin.

     

猕猴桃片冻干—真空微波联合干燥过程中品质变化及收缩模型

以猕猴桃为原材料,利用冻干—真空微波联合干燥的方式,选取不同的微波功率(0.25,0.30,0.39 W/g),结合猕猴桃在干燥过程中的收缩比、感官品质、色差、复水比、孔隙率等,分析猕猴桃片在干燥过程中的干燥特性、孔隙结构和收缩特性,建立猕猴桃片冻干—真空微波干燥过程中的收缩模型。研究结果表明,不同微波功率下,猕猴桃片的干燥特性有很大差异,微波功率越大,猕猴桃片的感官评分越高,色差越小,复水比越大,收缩比也越大,即达到干燥终点的体积越大,且猕猴桃片的孔隙率也越大。随着干燥的进行,猕猴桃片的水分含量越低,收缩比越小。猕猴桃片的最佳收缩模型为SR=k_1+k_2MR+k_3(MR)~2,R~20.99,RSS0.001,能很好地反映猕猴桃片在冻干—真空微波联合干燥过程中体积收缩的变化。