Comparison of the effect of microwave freeze drying and microwave vacuum drying upon the process and quality characteristics of potato/banana re‐structured chips

This study investigated the drying characteristics of microwave freeze‐drying (MFD)/microwave vacuum drying (MVD) of banana/potato restructured chips of varying proportion and microwave power. The results showed the MFD drying time had a maximum one‐hour time difference between the samples treated with 2 W g^?1 and 3 W g^?1 microwave power; and the higher potato content samples have about 30 min predominance than low potato content samples in drying time and the total drying time of MVD samples was less than 60 min. For the rehydration ratio, MFD samples were far superior to the MVD samples. The MFD samples had more than 4.5 rehydration ratio. The data of the colour difference metre showed that 3 W g^?1 microwave power would make samples slightly charred. The biggest differences between the MFD and MVD chips lie in their texture and shape; the hardness of MVD samples was 30.86 N, thrice higher than MFD samples.     

Novel microwave–freeze drying of onion slices

The present study aimed to introduce the capability of a novel dehydration technique. To do so, slices with various thicknesses (3.5 and 7 mm) of white onions were dried using commercial freeze drier (abs. pressure 0.005 mbar, temp. 45 °C), our own designed microwave-vacuum drier (abs. pressure down to 300 mbar) under various microwave powers (120–1200 W) and microwave-vacuum–freeze drier (onion slices kept at −20 °C for 2 h). Then, their dehydration rates and some quality parameters, such as rehydration ratio, colour ( L*, a* and b* ) and micro-structure were investigated. Our findings showed that microwave-vacuum–freeze drier is practically a rapid, simple, efficient, economic and novel dehydration technique which can be used for dehydration of mainly foodstuffs. The quality properties of slices produced by this novel method were also completely comparable and competitive with commercial freeze drier with over 96% saving on processing time and enormous amount on energy and capital investments.     

发展冻干食品企业的问题和建议

简述了国内外冻干食品行业发展概况和中国冻干食品企业的优势，指出中国冻干食品企业建立和运行过程中存在的一些问题，分析其原因，并提出解决这些问题的具体建议。最后介绍了清华大学核能技术设计研究院在食品真空冷冻干燥方面的研究工作。     

Changes of microwave structure/dielectric properties during microwave freeze‐drying process banana chips

This experimental study investigated the trend of structure and dielectric properties during microwave freeze‐drying process banana chips. The mass of banana samples was 160 g, the microwave power set as 2 W g^?1 and the highest drying temperature set as 55 °C. The whole drying process can be finished within 6 h. A network analyser and light microscope were used to determine the dielectric properties and structure. The dielectric properties, ε′ (from 20.80 to 1.20) and ε′′ (from 7.74 to 0.15), and the size of cell get smaller as the drying process continues, especially during the 3–4 h drying, which is the end of primary drying stage and the beginning of secondary drying stage. The trend of dielectric properties and microstructure of samples during drying can be an exact indication of drying stage of MFD.     

高菜真空冷冻与热风联合干燥工艺研究

研究真空冷冻(FD)与热风(AD)联合干燥腌制调味高菜,以期找到能生产优质节能的脱水腌制调味高菜的联合干燥方式.将联合干燥得到的产品分别与AD和FD干燥得到的产品进行总能耗和物理特性(包括复水比、色泽、体积密度以及产品的硬度和脆度)的比较,研究结果表明,FD20h+ AD1h的产品与FD的产品在品质上无显著差异,比FD干燥方式节省能耗约33％;AD1h+ FD22h比FD干燥方式节省能耗约22％,与FD的产品在色泽上有显著差异.两种联合干燥方式的产品最终湿基水分含量均达到了小于8％的要求,复水比均大于5.     

Effect of blanching on microwave freeze drying of stem lettuce cubes in a circular conduit drying chamber

Effects of boiling water and microwave blanching methods on the dielectric properties, electrical conductivity as well as microstructure of stem lettuce cubes (as a model for plant tissue) were studied. The study also focused on how different blanching methods affect microwave freeze-drying (MFD) in a circular conduit drying chamber and conventional freeze drying (FD) of stem lettuce cubes. Results showed that the electrical conductivity of samples blanched by microwave was two times higher than that of boiling water blanched ones and five times higher than that of unblanched samples. Apart from that, dielectric constant (ε′) and loss factor (ε″) of the stem lettuce cubes decreased significantly after freezing. MFD duration of microwave blanched samples was approximately 4.5 h, reduced by 30% compared to boiling water blanched ones. MFD process in a circular conduit yielded products of high quality compared to that in a tray.     

Effect of food ingredient on microwave freeze drying of instant vegetable soup

The objective of this work was to study the effect of three different food ingredients viz. NaCl content (1-15 g/100 g water), sucrose content (5-25 g/100 g water) and sodium glutamate content (0.5-10 g/100 g water) on microwave freeze drying (MFD) of instant vegetable soup. Response surface methodology (RSM) was employed to optimize their addition levels in instant vegetable soup for MFD. Finally, a comparison of MFD for instant vegetable soup with and without added ingredients was carried out. The results showed that NaCl content and sucrose content had significant influence on drying time and sensory quality, while sodium glutamate content had insignificant effect. The optimum ingredients of the instant vegetable soup for MFD were: NaCl content of 3.2-5.3 g/100 g water, sucrose content of 2-6.8 g/100 g water and sodium glutamate content of below 4.5 g/100 g water. Comparing with MFD vegetable soup without ingredients, condiments addition could increase drying rate and shorten drying time.     

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。     

林蛙油真空冷冻干燥工艺研究

以林蛙油为原料,采用真空冷冻干燥技术对林蛙油进行冷冻干燥。试验结果表明,在干燥室压力20Pa、物料的预冻速度为1.5℃/min,加热温度70～80℃时的条件下,冻干林蛙油复水率可达27.39%,蛋白质43.39%。     

冷冻干燥对牛乳脂肪酸及异构体成分的影响

通过薄层色谱、气相色谱检测方法,对呼和浩特地区牛乳以及其冷冻干燥样的脂肪酸组成进行检测分析,结果新鲜牛乳和其冷冻干燥样品的饱和脂肪酸、不饱和脂肪酸以及共轭亚油酸含量极为相近。冷冻干燥对牛乳脂肪酸及异构体成分基本没有影响。     

微波干燥技术在筒子纱线中的应用

自行研制微波于燥设备并用其干燥筒子纱卷,研究微波干燥设备的干燥效率及干燥效果,探讨其在纺织染整行业应用的可行性,为微波干燥在纺织染整行业的应用提供研究基础.经实验发现,微波干燥筒子纱的效率高于1.1 kg(水)/(kW·h)(微波).微波干燥后,纱卷含水均匀,纱线的强力和手感得到改善,微波干燥节能效果显著,比射频节能2...     

真空冷冻干燥香芋脆片生产工艺研究

以槟榔香芋为原料,研究了冻干香芋脆片的生产工艺。结果表明:采用0.2%柠檬酸做护色,3min微波熟化的真空冷冻干燥香芋片,可以保持原有的色、香、味、形。香芋片的共晶点为-13～17℃,共融点为-11～15℃;预冻温度应低于-22℃,冻干过程为60℃加热升华285min,然后升温至75℃,在此温度下解析105min;冻干过程真空度恒定为60Pa,冷阱表面温度设置为-40～-45℃,热水罐温度高于加热板温度5～10℃。     

食品真空冷冻干燥机加热系统

介绍了新一代食品真空冷冻干燥实验机NTFD05E加热系统的结构、设计的参数及计算过程,并通过一系列冰实验得到了加热板与加热功率的关系图,从而验证了加热系统的性能要求。     

青胡椒冷冻干燥工艺的优化

通过分析影响青胡椒冷冻干燥过程的因素,选取预冻时间、料盘装载量和干燥室真空度作为优化青胡椒冷冻干燥工艺的三个因素,并以冷冻干燥速率为指标,利用三因素三水平的响应面分析法优化了青胡椒冷冻干燥工艺条件并建立了回归模型.得到青胡椒冷冻干燥的最优条件为预冻时间6h、料盘装载量40 g、干燥室真空度20 Pa,在此条件下,冷冻干燥速率为0.05905％/h.     

保加利亚乳杆菌冷冻干燥粉不同复壮方法的比较

保加利亚乳杆菌冷冻干燥粉用１０％番茄脱脂乳培养基复壮,菌种的产酸量高,发酵活力恢复较好。     

杏鲍菇热风—真空冷冻干燥工艺优化

为了提高杏鲍菇干燥速率、品质及降低能耗,采用Design-expert软件的Box-Benhnken方法设计,探讨热风温度、热风时间、真空冷冻干燥时间对干燥速率、感官得分、复水比和氨基酸的综合影响,在该基础上由试验数据推导出二次多项式回归模型,并对干燥工艺条件进行优化。结果表明:热风干燥温度55℃、热风时间54 min,真空冷冻干燥时间11h。联合干燥耗时和耗能分别比真空冷冻干燥减少25.5%,6.3%,比热风干燥减少156.4%,63.3%。     

Effect of salt and sucrose content on dielectric properties and microwave freeze drying behavior of re-structured potato slices

Potato puree was used to prepare re-structured potato slices. The effect of salt and sucrose content on microwave freeze drying (MFD) and the variation of the dielectric properties of the potato slices were studied. Results showed that the dielectric constant (ε′) and loss factor (ε″) of the potato purees decreased significantly after freezing. Both salt and sucrose addition increased ε′ and ε″ of the samples at low temperatures (−25 to −5 °C). The salt content had greater influence relative to sucrose content on dielectric properties of the samples. Sucrose addition shows insignificant influence on dielectric properties of the thawing samples; while for the salted samples, ε′ decreased gradually with increasing salt content and ε″ increased significantly with increasing salt content and temperature. MFD drying rate was significant higher after adding salt and sugar.     

微波干燥粮食的研究

介绍了微波干燥原理和特性以及加热系统,详细分析了微波对粮食干燥的作用机理,展望了其运用前景,以期加速微波技术在粮食干燥工程中的运用推广.