微波真空组合干燥技术的研究

微波真空干燥是综合微波干燥和真空干燥各自优点的一项新技术,将微波干燥的快速高效性和真空干燥的低温高质相结合,在真空条件下利用微波对物料进行干燥处理,从而实现物料的快速低温干燥。着重阐述了微波真空组合干燥技术的机理、特点、干燥动力学以及影响微波真空干燥的重要因素,并对微波真空组合干燥的应用研究进行了介绍。     

微波真空组合干燥在食品加工中的应用

微波真空组合干燥技术是将微波干燥和真空干燥或真空冷冻干燥技术结合起来,弥补了微波干燥过程中物料温度高导致热损伤、真空或真空冷冻干燥干燥时间长的缺点,使物料在较低温度下短时间内完成干燥过程,具有干燥温度低、营养成分损失少、干燥速度快等优点。本文针对微波真空冷冻干燥技术在食品加工中的应用,详细阐述了其干燥原理、干燥特点、干燥设备和未来的研究和发展方向。     

黑加仑真空冷冻与微波真空联合干燥工艺研究

以黑加仑为原料,对其进行了真空冷冻与微波真空联合干燥工艺的研究。结果表明：先真空冷冻后微波真空干燥（FDMV）的组合方式是可行的;联合干燥合理工艺参数为：微波功率1．34kW。绝对压力11kPa,转换含水率为20％（wb）;通过试验验证,联合干燥生产的脱水黑加仑的感官品质和营养成分接近真空冷冻干燥,联合干燥方式对节省干燥时间和降低能耗是有效的。     

果蔬微波联合干燥技术研究进展

介绍了微波干燥的原理和特点，综述了果蔬微波联合干燥技术的研究进展，主要涉及到微波干燥与其它干燥技术联合在果蔬干燥中的应用。     

胡萝卜微波真空干燥试验研究

以胡萝卜为原料，采用均匀设计对微波真空干燥的微波功率、干燥温度及料层厚度进行试验研究，分析各试验条件下的水分含量及胡萝卜素含量，得到了干燥曲线和胡萝卜素保有量曲线，得出了胡萝卜失水量、胡萝卜素含量与各因素之间的回归方程，可用于描述胡萝卜的微波真空干燥特性。     

微波真空干燥技术现状

阐述了国内外微波真空于燥的研究现状，重点分析了脉冲微波真空干燥(间歇式微波干燥)的主要参数脉冲比、真空度、微波功率和能量效率。对微波真空于燥技术的发展提出了个人的看法。     

微波真空干燥器

<正> 日本Hosokawa公司将微波技术用于真空干燥器获得成功,业己生产出Vrieco-Nauta系列微波真空干燥器,使用微波真空干燥效率大大提高,与普通干燥器相比,微波真空干燥时间短,只需原来的50—70％,干燥制品质量明显改善,制品内含湿量均匀。由于微波真空干燥器的结构和工作原理不同     

响应曲面法漂白紫胶微波-真空干燥工艺研究

为提高漂白紫胶产品质量及生产效率,采用微波-真空干燥漂白紫胶研究了不同压强、微波功率和干燥时间对漂白紫胶产品颜色指数和含水率的影响,用响应曲面法（RSM）设计试验并建立了该工艺条件的拟合方程。结果表明,拟合方程的拟合度较高,所建立的数学模型可以用于描述漂白紫胶的微波-真空干燥。漂白紫胶微波-真空干燥的最优条件：干燥压强为3.0 kPa,微波功率为795 W,干燥时间为30 min。在优化条件下进行了验证实验,得到了颜色指数为0.9、含水率为0.028 9kg水/kg干料的产品。     

微波真空干燥工艺参数对猕猴桃切片品质的影响

微波真空干燥技术是在真空条件下利用微波能对物料进行干燥加工的一项新技术,本实验以猕猴桃切片为研究对象,以干制品复水率、维生素C含量以及干燥时间为指标,在单因素试验的基础上,通过3因素3水平的二次回归正交试验,研究了微波功率、物料厚度、干燥室压力对猕猴桃切片干燥特性的影响。结果表明：在微波功率为800W、切片厚度为4mm、干燥室压力为0．04MPa的条件下,微波真空干燥猕猴桃切片的干制品质量最好,确定了猕猴桃切片微波真空干燥较优工艺参数条件。     

干燥方式对红枣动力学及挥发性成分的影响

采用热风干燥、真空冷冻干燥和微波真空干燥对红枣进行干燥处理，结合顶空固相微萃取-气相色谱-质谱（headspace solid-phase microextraction-gas chromatography-mass spectrometry，HS-SPME-GC-MS）和电子鼻对枣片挥发性成分进行了分析，并对比了3种干燥方式对红枣色泽、动力学和挥发性成分的影响。结果表明，热风干燥和微波真空干燥对枣片色泽影响较大，真空冷冻干燥能够更好的保持原始色泽；对动力学方程进行拟合，发现Page 模型为预测红枣3种干燥方式干燥特性最适合的数学模型；干燥对枣片挥发性成分种类及相对含量差异显著，其中干燥前后相同的挥发性成分有19种。挥发性物质主要有酸类、酯类、醇类、醛类、酮类、烃类、杂环类和其他化合物，干燥过后枣片中酸类和烷烃类挥发性成分相对含量显著增加，醛类和杂环类物质显著降低。电子鼻结果表明干燥后枣片香气特征与新鲜红枣有较大的区别，热风干燥和微波真空干燥香味特征较为接近，微波真空干燥枣片的焦甜香特征更为明显。相较于热风干燥和真空冷冻干燥，微波真空干燥效率较高、能耗较低、周期较短，更适于制备干燥枣片。     

Effects of Different Drying Methods on the Quality Changes of Granular Edamame

In this article, the quality changes of the granular fruits and vegetables dried by vacuum microwave drying, freeze drying, hot air drying, and combined hot air–vacuum microwave drying are investigated, and the quality parameters compared on the basis of vitamin C and chlorophyll contents, shrinkage and rehydration capacity, color, texture, and microstructure changes. The quality parameters of products dried by vacuum microwave drying are slightly lower than those obtained by freeze drying, but much better than those obtained using conventional hot air drying. The quality characteristics of product dried by combined hot air–vacuum microwave are significantly improved compared to those simply hot air–dried.     

Effects of Different Drying Methods on the Quality Changes of Granular Edamame

In this article, the quality changes of the granular fruits and vegetables dried by vacuum microwave drying, freeze drying, hot air drying, and combined hot air-vacuum microwave drying are investigated, and the quality parameters compared on the basis of vitamin C and chlorophyll contents, shrinkage and rehydration capacity, color, texture, and microstructure changes. The quality parameters of products dried by vacuum microwave drying are slightly lower than those obtained by freeze drying, but much better than those obtained using conventional hot air drying. The quality characteristics of product dried by combined hot air-vacuum microwave are significantly improved compared to those simply hot air-dried.     

Microwave-Assisted Drying of Biomaterials

Drying of biological materials such as fruits and vegetables provides shelf-stable commodities ensuring food security and ease of distribution. There exists numerous drying processes available for the adequate drying of bio-materials. Applying microwave energy to a drying process provides an efficient means of transferring energy for moisture removal. A review of recent microwave assisted drying applications is presented here along with research results on drying of carrots under varying microwave power modes and the comparative drying of mushrooms by microwave/convection and microwave/vacuum.     

THE EFFECT OF PROCESS CONDITIONS ON THE DRYING KINETICS AND REHYDRATION CHARACTERISTICS OF SOME MW-VACUUM DEHYDRATED FRUITS

The effect of drying conditions, namely, microwave power, vacuum pressure, as well as sample geometry, on the drying kinetics and rehydration characteristics of five microwave vacuum dehydrated fruits (apple, avocado, mushroom, pear and strawberry) was studied. The investigation involved a wide range of microwave power, vacuum pressure and sample size levels. The drying rate and the rehydration ratio, a measure of rehydration characteristics, were found to depend on the drying conditions. An empirical mass transfer model, involving a characteristic parameter for each process (drying and rehydration( as a function of process variables, namely, microwave power, vacuum pressure and sample size, was also tested with the data obtained in a microwave oven equipped with vacuum apparatus. Furthermore, a comparison of rehydration properties of microwave vacuum and conventionally dehydrated products, was conducted.     

THE EFFECT OF PROCESS CONDITIONS ON THE DRYING KINETICS AND REHYDRATION CHARACTERISTICS OF SOME MW-VACUUM DEHYDRATED FRUITS

ABSTRACT

The effect of drying conditions, namely, microwave power, vacuum pressure, as well as sample geometry, on the drying kinetics and rehydration characteristics of five microwave vacuum dehydrated fruits (apple, avocado, mushroom, pear and strawberry) was studied. The investigation involved a wide range of microwave power, vacuum pressure and sample size levels. The drying rate and the rehydration ratio, a measure of rehydration characteristics, were found to depend on the drying conditions. An empirical mass transfer model, involving a characteristic parameter for each process (drying and rehydration( as a function of process variables, namely, microwave power, vacuum pressure and sample size, was also tested with the data obtained in a microwave oven equipped with vacuum apparatus. Furthermore, a comparison of rehydration properties of microwave vacuum and conventionally dehydrated products, was conducted.     

MICROWAVE VACUUM DRYING KINETICS OF SOME FRUITS

Microwave vacuum drying kinetics of three fruits (namely, apple, kiwi and pear) were studied by introducing an one-parameter empirical mass transfer model, involving a characteristic parameter (drying constant), as a function of process variables. The model was tested with data produced in a microwave oven equipped with vacuum apparatus, using non-linear regression analysis. The investigation involved a wide range of microwave power and vacuum pressure levels. The parameters of the model considered were found to be greatly affected by the microwave power level while vacuum pressure affected slightly the process.     

New understandings of how dielectric properties of fruits and vegetables are affected by heat-induced dehydration: A review

Abstract

Dielectric heating (DH) is an alternative to traditional conductive heating. Preservation of fruits and vegetables through drying based on DH is faster than conventional heating systems, needing less processing time, and delivering a better dehydrated product as well as reduced treatment costs. Dielectric properties (DPs) are significant physical qualities that are affected by microwave (MW) and radio frequency (RF) heating systems; these attributes directly affect the electromagnetic arrangement and currents surrounding the materials. In other words, DPs define the response of materials in electric fields at the desired frequency and temperature. Thus, DPs of materials are of increasing interest in the agricultural and food-processing fields. The principles of the DPs of fruits and vegetables according to frequency, temperature, and composition are crucial in the designing and handling of MW and RF heating operations. A consideration of DPs is required to ensure the quality of fruits and vegetables is enhanced throughout the drying process for better quality final products. This review aimed to provide a comprehensive update on the prospects of DH for drying of fruits and vegetables. The factors that affect the DPs during the dehydration process of fruits and vegetables and discussions about the correlation among these factors were also provided. In addition, the fundamentals of DPs and their measurement techniques were also discussed. This study is an update on the state-of-the-art DH system and illustrates the important influence of DPs on the radiative heating of fruits and vegetables.     

A comparative study of drying methods on physical characteristics,nutritional properties and antioxidant capacity of broccoli

Abstract

Broccoli is considered one of the attractive raw materials for dehydrated vegetables owing to its high nutritional value. However, information about how drying methods affect the physicochemical and nutritional properties of broccoli is limited. In this study, broccoli pieces were subjected to freeze drying (FD), hot air drying (HAD), microwave vacuum drying (MVD), vacuum drying (VD), MVD combined with HAD (MVD?+?HAD), and MVD combined with VD (MVD?+?VD). Quality attributes of dehydrated broccolis were contrasted in terms of color, texture, volume shrinkage, nutritional components, antioxidant activity, and rehydration capacity. Results demonstrated that FD better preserved the nutrients while HAD displayed the worst effect. The combination of MVD?+?HAD and MVD?+?VD resulted in higher retention of nutritional compositions, better antioxidant activity, and lower energy consumption than that of HAD. Furthermore, combined drying processing exhibited similar rehydration capacity but lower hardness compared to that of HAD.     

MICROWAVE VACUUM DRYING KINETICS OF SOME FRUITS

ABSTRACT

Microwave vacuum drying kinetics of three fruits (namely, apple, kiwi and pear) were studied by introducing an one-parameter empirical mass transfer model, involving a characteristic parameter (drying constant), as a function of process variables. The model was tested with data produced in a microwave oven equipped with vacuum apparatus, using non-linear regression analysis. The investigation involved a wide range of microwave power and vacuum pressure levels. The parameters of the model considered were found to be greatly affected by the microwave power level while vacuum pressure affected slightly the process.