Comparison of four drying methods for re-structured mixed potato with apple chips

The effects of microwave-freeze drying (MFD), freeze drying (FD), microwave vacuum drying (MVD) and vacuum drying (VD) on texture, color, rehydration, sensory, microstructure and other quality parameters of re-structured chips made by blending apple with potato were studied. MFD chips had the best quality and these products were preferred by consumers. The drying time for MFD was lower than that for FD. The drying time for MVD was the shortest and the energy consumption was also the lowest. Microwave drying not only reduces the drying time but also improves the quality of dried products. Both MFD and MVD techniques are found to be suitable for production of re-structured chips of varying grades.     

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.     

海参冻干-微波联合干燥技术研究

由于海参离开海水后很快会发生自溶,所以海参一般都是脱水后在市场上流通。传统的海参干制方法耗时太长,而且品质较差;真空冷冻干燥方法可以获得品质优良的海参干制品,但能耗太大。为了缩短冷冻干燥的干燥时间,同时保证海参的干燥质量,将海参真空冷冻干燥至一定含水率,再进行真空微波干燥,并与其他典型干燥方法进行了比较,发现微波-冻干联合干燥方法能有效缩短冻干时间,其产品和常规冻干产品无明显差异。     

Analysis of Temperature Distribution and SEM Images of Microwave Freeze Drying Banana Chips

Compared with freeze drying (FD), microwave freeze drying (MFD) using microwave as the heating source can accelerate the drying rate of bananas. This paper presents the results of an experimental study of temperature distribution during the process of MFD banana chips. The results show that the temperature distribution is uniform during the sublimation drying stage, but not at the start of the desorption stage of drying; this phase is prone to generate hot spots, which are brought about by the localized melting of ice crystals not removed in the sublimation stage and the absorption of excess microwave by sorbed water. Comparison of scanning electron microscope micrographs of FD and MFD samples shows that the major dissimilarity between the two samples is in their pore sizes.     

Recent developments in high efficient freeze-drying of fruits and vegetables assisted by microwave: A review

Microwave heating has been applied in the drying of high-value solids as it affords a number of advantages, including shorter drying time and better product quality. Freeze-drying at cryogenic temperature and extremely low pressure provides the advantage of high product quality, but at very high capital and operating costs due partly to very long drying time. Freeze-drying coupled with a microwave heat source speeds up the drying rate and yields good quality products provided the operating unit is designed and operated to achieve the potential for an absence of hot spot developments. This review is a survey of recent developments in the modeling and experimental results on microwave-assisted freeze-drying (MFD) over the past decade. Owing to the high costs involved, so far all applications are limited to small-scale operations for the drying of high-value foods such as fruits and vegetables. In order to promote industrial-scale applications for a broader range of products further research and development efforts are needed to offset the current limitations of the process. The needs and opportunities for future research and developments are outlined.     

基于iTRAQ技术的鸡蛋清三种干燥方式差异蛋白质组分析

为探究真空冷冻干燥(vacuum freeze-drying, FD)、喷雾干燥(spray-drying, SD)和微波真空冷冻干燥(microwave vacuum freeze-drying, MFD)3种干燥方式对蛋清蛋白的差异,利用iTRAQ技术对三者进行蛋白质组差异分析,在得到的157种具有定量信息的蛋清蛋白中,鉴定出87种差异蛋白。MFD vs FD组上调蛋白质数量为46个,占差异蛋白质总数的67.6%。KEGG富集显示,MFD vs FD组和MFD vs SD共有2个基因通路显著富集,分别为折叠和降解、运输和分解代谢。此外,在差异蛋白中筛选出4种蛋白质在干燥过程中丰度变化显著,分别为黏蛋白、血清白蛋白、卵清蛋白相关蛋白Y亚型X1和卵白蛋白相关蛋白Y。该研究首次采用蛋白质组学的方法分析不同干燥方式处理后的鸡蛋清差异蛋白的表达变化,为今后生产和开发高品质蛋清粉及功能性蛋制品提供参考依据。     

A novel strategy for improving drying efficiency and quality of cream mushroom soup based on microwave pre-gelatinization and infrared freeze-drying

The present study was carried out to achieve a more efficient dehydration process along with low undesirable quality decrease for cream mushroom soup (CMS) by combining microwave pre-gelatinization (MPG) with infrared freeze-drying (IRFD). Wheat flour was gelatinized using a microwave heating unit for different times, and was used in CMS formulations. Freeze drying (FD) was carried out using conventional as well as IRFD and drying time, energy consumption and product quality characteristics (flavor, viscosity of rehydrate juice; moisture absorption and crystallinity of dried soup solid) of CMS were studied. Compared to FD, IRFD reduced the drying time and energy consumption by 23.81% and 28.43%, respectively. The microwave pre-gelatinization of wheat flour and subsequent use in IRFD, while in comparing with single infrared freeze drying, did not affect drying time and energy consumption; however, it significantly improved the flavor and viscosity of soup upon rehydration, and reduced the tendency to retrogradation. The microwave pre-gelatinization time of 120 s at 8 W/g energy level was found to be the most suitable condition for microwave pre-gelatinization of wheat flour.Industrial relevanceUndesirable decrease of viscosity in starch containing soup and high energy consumption of traditional freeze-drying limit the large-scale industrial production of freeze-dried starch containing product. Therefore, inhibiting viscosity reduction and reducing production cost are the crucial steps for industrial production of freeze-dried cream mushroom soup. Microwave pre-gelatinization and infrared freeze-drying have made outstanding contributions on improving starch stability and reducing drying energy consumption, respectively, which caters to the preferences of industrial production and can be used in industrial production of freeze-dried instant cream mushroom soup.     

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.     

微波冷冻干燥传热传质模型的研究进展

微波冷冻干燥技术是一种快速干燥脱水技术,可应用在一些特定食品上,尤其是海产品、水果和蔬菜等。与传统冷冻干燥技术相比,微波冷冻干燥可节约干燥时间和能量,提高产品质量。文章主要介绍微波冷冻干燥的原理、国内外对其传热传质数学模拟的研究进展及在线检测技术,同时在干燥模拟过程考虑物料的介电特性,分析问题所在,并展望微波冷冻干燥数学模拟的发展方向。     

不同干燥方式对铁棍山药品质的影响

以外观、营养成分、复水性及超微结构为指标,比较4种不同的干燥方式对铁棍山药品质的影响。冻干(FD)对铁棍山药品质的保留最好,冻干真空微波联合干燥(FD-MVD)对产品品质的保留接近于FD,且能够使干燥时间缩短31%。微波真空干燥时间最短,但品质不如前两种干燥方式。热风干燥(AD)对感官品质和维生素C破坏较多,但对于多糖含量的保持与其它方法无异。超微结构的结果表明,MVD和AD对结构破坏较多,而FD和FD-MVD很好的保持了原有的细胞结构。     

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.     

Temperature and power control in microwave drying

A microwave drying system with the ability of automatic temperature and power control was developed for apple drying. The samples’ mass and the moisture content could be obtained online. Four different drying modes were attempted with different combination of temperature and power controls. Feedback temperature control with predefined variable power profiles resulted in the best temperature control and product quality. All other modes proved their own pros and cons. The study also verified that it was difficult to maintain a constant temperature during microwave drying process when a feedback temperature control was not included. The results can be used to determine microwave power levels in microwave drying practices both with and without temperature control.     

Microwave-drying of sliced mushroom. Analysis of temperature control and pressure

The drying of sliced mushroom by microwave energy is studied for different operational conditions related to temperature control position and pressure and their effects on drying kinetics and quality. Thinly sliced mushrooms were dried in a guide cavity by applying microwave energy at 2.45 GHz. The influence on the quality of the dehydrated mushrooms was studied by two different techniques: sorption isotherms (Halsey and B.E.T. equations) and scanning electron microscopy (SEM). Drying kinetics were also analyzed through the determination of diffusivity by applying a mathematical model that takes into account changes in moisture on the product surface during the process. Thus, the results of SEM observations and quality can be linked with diffusivity values in each experiment. As a rule, the operational conditions imposed result in contrary tendencies in quality and drying kinetics. High heat levels usually lead to unfavorable quality results in the dehydrated product if not corrected with a favorable inverse temperature gradient characteristic of microwave heating.Industrial relevanceThe combination of drying and enzyme inactivation of mushrooms browning confers microwave drying a great interest with regard to its industrial application. The results referenced in this paper, concerning the position effect of temperature control and pressure will contribute to the continued development of microwave technology applied to food dehydration.     

Effect of Convective and Vacuum–Microwave Drying on the Bioactive Compounds,Color, and Antioxidant Capacity of Sour Cherries

The aim of this study was to determine the effect of microwave power during the vacuum–microwave drying (VMD) on sour cherries in terms of drying kinetics, including the temperature profile of dried material, as well as on some quality factors of the finished product including phenolic compounds, antioxidant capacity, and color. The content of phenolic compounds, antioxidant activity, and color change were used as quality indicators of dried sour cherries. Sour cherries were dehydrated by convective drying (CD) at temperatures of 50 °C, 60 °C, and 70 °C and by VMD at the initial microwave power of 240 W, 360 W, and 480 W reduced to 240 W and 120 W in order to avoid a rapid increase in temperature at the critical moisture content of ca. 1 kg/kg dry mass. Control samples were prepared by freeze drying (FD). The increase in air temperature during CD as well as the increase in material temperature during VMD deteriorated dried product quality in terms of the content of phenolic compounds, antioxidant activity, and color, which was consistent with anthocyanins content. However, VMD turned out to be much better than CD and competitive to FD. The best quality of the dried product and its more attractive color were achieved at VMD at 480 W followed by drying at microwave power reduced to 120 W, which corresponds to anthocyanins content. In addition, the drying process had a positive impact on contents of quercetin and keampferol derivatives. Dried sour cherries have a long shelf life and therefore may be a fine alternative to fresh fruit all year round.     

Physico-chemical changes during different stages of MFD/FD banana chips

Microwave freeze drying (MFD) normally contains three stages, i.e., pre-freeze stage, primary drying stage and secondary drying stage, just as in conventional freeze drying. This research examines the variations of structure, starch content, reducing sugar content, color change as well as expansion ratio during these stages of microwave freeze drying banana chips. Results show that biggest changes are found at the primary drying stage in the banana slices’ starch content, reduced sugar content, their structure and their changed colors while the biggest change of expansion ratio occurs at the secondary drying stage. Similar results can also be obtained for FD samples. Thus it is concluded that the primary stage can do most damage to the banana chips.     

Power density control in microwave assisted air drying to improve quality of food

Currently, the new trend is the development of microwave hot air drying control in order to solve the problem of hot spots on the product. So in this study, a microwave/hot air drying system with the ability of automatic power density control was developed for tomato drying. Three power densities (3, 5 and 7 W/g) at 40 °C air temperature were applied and the output, reflected microwave power and the mass of the sample were registered online. Two different drying strategies were implemented. The first consisted of a microwave drying without specific power control. The second one introduced power control. A feedback control based on specific power related to the actual sample mass resulted in the best power control and the improvement of product quality compared to the dry sample without power control.     

A novel dielectric drying method of sea cucumber

The sea cucumber autolyses readily so it must be dehydrated for preservation. Traditional drying methods of sea cucumber need very long time and have adverse effect on quality. Hence, a novel microwave freeze drying technique was developed to dry sea cucumber. Because microwave heating is a function of dielectric properties of the material in microwave field, dielectric properties of sea cucumber were determined. As expected, the dielectric loss factor of sea cucumbers was very low in frozen state, and several pretreatments (nanoscale calcium carbonate impregnation and vacuum impregnation, salt impregnation, etc.) were analysed to improve the dielectric properties of sea cucumber. Vacuum impregnation with nanoscale calcium carbonate combined with microwave freeze drying was found to be an efficient drying method for sea cucumber by anova (P < 0.01). Compared with microwave freeze drying method without any treatments, this drying method could reduce the drying time by up to two hours.     

Stability of quercetin derivatives in vacuum impregnated apple slices after drying (microwave vacuum drying,air drying,freeze drying) and storage

Microwave vacuum drying (MVD) was investigated for apple slices enriched with quercetin derivatives by vacuum impregnation (VI). Additional freeze drying (FD) and air drying (AD) were conducted. Compared to native apples, the impregnated tissue resulted in higher moisture content, elevation of weight and significant browning, due to the incorporated VI solution. The total quercetin content and quercetin glycoside composition were not affected by MVD and FD. The vacuum conditions protect the polyphenols from oxygen dependent degradation and browning reactions. AD resulted in an average quercetin glycoside loss of 44% and undesirable changes, particularly discoloration. The degradation is caused by both non-enzymatic and enzymatic reactions. The pulsed microwave energy intake improved the drying result in structure and led to a faster drying process of 130 min. The bulk density of MVD apple chips (0.69 g/ml) ranged between 0.33 g/ml for FD and 0.75 g/ml for AD. The final moisture content was the lowest after FD (6.8 g/100 g), followed by 9.0 g/100 g after MVD and 12.7 g/100 g after AD. The shelf life was significantly influenced by storage temperature and time. After 12 month at 20 °C, the total quercetin content decreased by 21%.     

微波-热风联用制取笋干工艺条件优化

为获得干燥时间短、干燥品质好的笋干,以竹笋为原料,在单因素试验的基础上,根据中心组合试验设计原理,分析微波干燥功率、微波干燥时间和热风干燥温度3 个因素对笋干感官评分、总干燥时间、复水比、色差和硬度指标的影响,以确定微波-热风联用制取笋干最佳工艺条件。结果表明,制取笋干的最佳工艺条件为：微波干燥功率6.3 W/g、微波干燥时间60 s、热风干燥温度65 ℃。在此条件下得到的笋干感官评分85.6、总干燥时间200 min、复水比6.17,干制品色差ΔE* 19.99、复水制品色差ΔE* 13.92、干制品硬度19 511.23 g、复水制品硬度20010.71 g,该工艺研究结果可为笋干产业化发展提供理论支持。     

Microwave drying characteristics of potato and the effect of different microwave powers on the dried quality of potato

Little detailed information is available on the microwave drying characteristics of potato and the use of different microwave powers to dry food products. Experiments were conducted to study the microwave drying characteristics and the dried quality of potato. The study focuses on describing the microwave drying characteristics of potato and discussing the effect of sample thickness, drying power and mass. The results show that if the power level increases, the mass load decreases and the thickness of the sample decreases, the dehydration rate increases and the drying energy consumption decreases. There are two falling rate periods during microwave drying of potato: the first falling rate period is for a moisture content of more then 1.1 (dry basis, DB); the second falling rate period is for a moisture content of less than 1.1 (DB). The same water loss will consume more energy when the moisture content is less than 1.1 (DB). A two-stage drying process was employed during microwave drying of potato. The microwave power of the first drying stage differed form that of the second drying stage. The moisture content of the breakpoint for the conversion of the first drying stage into the second drying stage is a moisture content of 1.1 (DB). A quadratic orthogonal regression experiment was conducted, and the effects of slice thickness, the first drying load power and the second drying load power on sensory quality, the rehydration ratio and the energy consumption rate were established. The slice thickness, the first drying load power and the second drying load power linearly affected the three indices. The effect of the product of the second drying load power and the potato slice thickness on the rehydration ratio and the energy consumption rate is significant. The optimum drying parameter combination for the three indices was obtained. The rehydration ratio of the dried products decreased with an increase of the second drying load power and the slice thickness. The concave curves of the sensory quality versus the three factors were shown.