The drying strategy of atmospheric freeze drying apple cubes based on glass transition

Freeze drying (FD) yields the best quality of dried apple cubes but at the cost of long drying time and also the overall cost. To achieve economical freeze drying along with a high quality product an atmospheric freeze drying (AFD) technique was developed to dry apple cubes. The effect of different air temperature loading scheme on product quality and drying process was studied during AFD. According to the glass transition temperature of apple, a step-up temperature loading strategy for AFD process was developed to reduce the drying time by almost half and provided a similar good product quality.     

The energy consumption and color analysis of freeze/microwave freeze banana chips

This study investigated the energy consumption of preparing banana chips by freeze drying (FD) and microwave freeze drying (MFD) methods. The results in this study showed that the energy consumption for 400 g fresh banana (about 95 g dried samples) by FD process and MFD process are about 35.73 × 10⁶ J (9.92 kW h) and 21.76 × 10⁶ J (6.57 kW h), respectively. Compared to the traditional FD process, MFD can save up to 35.7% energy and 40% drying time. Increasing the heating power in the secondary drying stage of MFD process had been confirmed to result in decrease in both the energy consumption and drying time. After increasing the microwave power in the secondary drying stage from 1.0 W/g to 1.5 W/g in MFD process, total energy consumption is about 18.12 × 10⁶ J (5.56 kW h) and drying time can be reduced from 360 min to 270 min. The sensory evaluation of produced banana chips at different drying conditions (1.0 W/g, 1.5 W/g and 2.0 W/g) revealed that the sensory properties are acceptable by the customers except the 2 W/g microwave power dried product. Thus, the method that increased the heating powder in the secondary drying stage of the MFD process could potentially be an effective method to reduce the energy consumption without seriously sacrificing the color of the end product.     

固态食品常压吸附流化冷冻干燥的研究

至今为止,冷冻干燥技术得到应用的只有真空冷冻干燥一种,本文提出了常压吸附剂流化冷冻干燥,并具体阐述了数学模型和实验装置。通过与真空冷冻干燥进行比较,认为常压吸附流化冷冻干燥值得进一步深入研究,具有发展和应用前景。     

Optimization of the microwave drying process for potato chips based on the measurement of dielectric properties

A microwave drying system with functions of automatic power and temperature control was developed to dry potato chips. The mass and moisture content of the sample are available online. The dielectric properties of the samples were measured during microwave drying, during which the microwave absorption capacity of the samples was analyzed. Afterward, a reasonable power and temperature control scheme was formulated. The enhanced microwave drying technology of potato chips is found by comparing product quality under different schemes. Results show that the change in the dielectric properties of materials during microwave drying is closely related to moisture and temperature variations. A three-stage different temperature control with predefined variable power profiles resulted in the best product quality.     

Browning behavior of button mushrooms during microwave freeze-drying

In order to achieve faster drying along with high product quality, microwave freeze-drying (MFD) was applied to dry button mushrooms. Although MFD can lead to similar product quality compared with freeze-drying (FD), the color deterioration of MFD mushroom is higher than FD ones. Therefore, two drying methods were used to investigate the browning behaviors of button mushrooms during MFD in terms of parameters including polyphenol oxidase activity, total phenolic content, moisture content, reducing sugar content, and vitamin C content. It was found that both whiteness and browning degree can be used to describe the browning kinetics of button mushrooms during the MFD process. Both nonenzymatic browning and enzymatic browning took place during MFD of button mushrooms, but the effect of enzymatic browning was more significant, which should be controlled during MFD. In order to avoid enzymatic browning during MFD of button mushrooms, a relatively low microwave power at initial stage of MFD should be adopted. Meanwhile, a low microwave power also should be used at the end stage of MFD so as to reduce nonenzymatic browning.     

Optimization of spray freeze drying parameters for spark plasma sintering of transparent MgAl2O4 spinel

Magnesium aluminate spinel (MgAl₂O₄) is considered as one of the most important spinels possessing desirable mechanical properties, with a wide range of applications at high temperatures. Powder granulation by spray freeze drying can lead to better powder flow and distribution in the mold, resulting in a specimen with high green density and strength. Accordingly, this study aimed at investigating the influential parameters on the granulation process of spinel powders via the spray freezing drying method. At first, spinel powders with various weight percents of 20, 25, 30, 35 and 50, and PVA binders with 0, 1, 2 and 8 wt% were investigated to prepare the optimal solution. Finally, the granules were sintered using the SPS method. The obtained bodies were tested by X-ray diffraction, SEM, FE-SEM, Viscosity and UV–Vis. The results showed that the optimal amount of the binder to obtain uniform granules in this process was 3%. Also, 35 wt% of solid loads represented the optimum amount for slurries, forming granules with the size range of 10–50 μm. By powder granulation, density experienced an increase of about 20%, leading to the growth of more than 15% in the in-line transmission for the IR range.     

Dielectric properties of thermosonically treated Agaricus bisporus slices during microwave vacuum drying and correlation with the water state

Abstract

The dielectric properties of thermosonically treated Agaricus bisporus slices during microwave vacuum drying were determined, by using a network analyzer and an open-ended coaxial-line probe at microwave frequency (915 and 2450?MHz). The permittivity at 25?°C was also correlated to the water state determined by low field nuclear magnetic resonance (LF-NMR) analysis. Results showed that the dielectric constant ε' and loss factor ε″ of A. bisporus slices were affected significantly by the composition of water state in the sample. Thermosonic pretreatment enhanced the influence of semi-bound water (M₂₂) and bound water (M₂₁) on the permittivities in sample slices during microwave vacuum drying (MVD). The dependency of permittivities on the moisture content and temperature at 915 and 2450?MHz for thermosonically treated A. bisporus samples could be described by third-degree polynomial models, with R² higher than 0.998. Infrared thermal imaging analysis confirmed that thermosonic pretreatment is a potential technology to promote the uniformity of A. bisporus slices during the MVD process.     

真空冷冻干燥法制备CuO-ZnO-ZrO2甲醇合成催化剂

采用真空冷冻干燥法制备了一系列CuO-ZnO-ZrO2甲醇合成催化剂,在微型固定床反应器上考察了其对CO2加氢合成甲醇的催化性能及影响,并用XRD、H2-TPR、CO2-TPD、TEM、EDAX、BET等手段进行了表征。研究结果表明,采用真空冷冻干燥法能够制备出高比表面积、高活性、高选择性的甲醇合成催化剂CuO-ZnO-ZrO2。     

文物冷冻干燥水蒸气扩散系数的测量

采用聚乙二醇(PEG)溶液进行预处理,然后加以冷冻干燥,是保护出土饱水木质文物的有效方法。在自制的冷冻干燥装置上进行了仿木质文物的冻干实验,根据实验数据拟合得到了干燥区的水蒸气扩散系数。该数据将为文物冻干过程的时间预测和控制优化提供帮助。     

Fabrication of transparent MgAl2O4 spinel via spray freeze drying of microfluidized slurry

Spherical granules were prepared from a monodispersed slurry by combining the microfluidization (MF) method and the spray freeze-drying (SFD) process. Starting with the prepared granules, transparent MgAl₂O₄ ceramics were fabricated through pressureless sintering followed by hot isostatic pressing. A comparison with a polydispersed slurry prepared by the ball-milling method showed successful fabrication of a mono-dispersed state by microfluidization method, and 80% visible in-line transmittance was obtained at a 600-nm wavelength from a process starting with a monodispersed slurry of low solid content. Microstructural analysis of the green bodies, the pre-sintered bodies, and the hot isostatic pressed bodies of the prepared MgAl₂O₄ ceramics revealed that the slurry dispersion should be controlled to a high level in order to suppress scattering sources such as pores and microcracks, which affect the in-line transmittance of visible light.     

Evaluation of Thin-Layer Models for Mushroom (Agaricus bisporus) Drying

In the present research, seven well-known mathematical thin-layer drying models were fitted to mushroom (Agaricus bisporus) drying experimental data, implementing nonlinear regression analysis techniques. The experiments were conducted in two laboratory-scale dryers. A range of temperatures 50-65°C and air velocities 1.0-5.0 m/s were tested. The statistical analysis concluded that the best model in terms of fitting performance was the logarithmic model. Correlations expressing this model parameter dependence with the drying air coefficients are also reported.     

Evaluation of Thin-Layer Models for Mushroom (Agaricus bisporus) Drying

In the present research, seven well-known mathematical thin-layer drying models were fitted to mushroom (Agaricus bisporus) drying experimental data, implementing nonlinear regression analysis techniques. The experiments were conducted in two laboratory-scale dryers. A range of temperatures 50–65°C and air velocities 1.0–5.0 m/s were tested. The statistical analysis concluded that the best model in terms of fitting performance was the logarithmic model. Correlations expressing this model parameter dependence with the drying air coefficients are also reported.     

On the investigation into the kinetics of the ultrasound-assisted atmospheric freeze drying of eggplant

Atmospheric freeze drying is a highly attractive process for the dehydration of thermosensitive products, like food, due to the fact that water is removed at low temperature by sublimation. Unfortunately, drying times can be very long because of the internal resistance of the product to vapor diffusion: power ultrasound can be an effective means of accelerating the process, thus reducing the operating cost. The aim of this study was to assess the effect of air temperature and velocity, ultrasound power and sample size on the drying kinetics of eggplant (Solanum melongena L.) samples and, afterward, to analyze in silico an industrial process. Experiments were performed under various conditions regarding air temperature (?5, ?7.5, ?10°C), velocity (2 and 5?m?s^?1), power ultrasound (0, 10.3, 20.5?kW?m^?3, 21.9?kHz), and sample size. Drying rate was measured experimentally. The air velocity showed no relevant effects on the drying kinetics, and the effect of air temperature was slight when compared to the marked reduction in the drying time obtained when ultrasound was applied. The uniformly retreating interface model was modified to account for the cubic shape of the samples and used to establish the kinetic parameters, in particular to evaluate water diffusivity in the dried product, searching for the best fit between measured and calculated moisture content. The model was finally used to optimize the process in silico, considering an industrial unit as test case. In this case, it appeared that power ultrasound can increase the productivity of a tunnel dryer up to four or five times, and it allows the operational and fixed costs of the plant to be reduced significantly.     

Effect of combined infrared freeze drying and microwave vacuum drying on quality of kale yoghurt melts

Abstract

Kale yoghurt melts are proposed as a novel snack that can melt in the mouth. However, such melts with thin fresh pulp were difficult to shape when drying at elevated temperature. In order to obtain a desirable shape and high-quality snack, freeze drying (FD), infrared freeze drying (IRFD), and combination of infrared freeze drying and microwave vacuum drying (IRFD-MVD) were attempted. The effects of these drying techniques on the drying time, energy consumption, bulk density, rehydration time, texture, color, chlorophylls, carotenoids and total phenolics contents as well as antioxidant activity and sensory characteristics of the differently dried products were compared. Nuclear magnetic resonance and magnetic resonance image analyses were also conducted to illustrate the state and proportion of water during the IRFD process. Drying time of IRFD was noted to be significantly shorter than that of FD. IRFD-MVD could further save the time as well as energy consumption of drying and, when properly conducted, could maintain the quality of snacks.     

Morphology of alumina granules obtained by spray freeze drying with twin-fluid atomization

This study presents the results of the morphological dependence of alumina granules obtained by spray freeze drying (SFD) with twin-fluid atomization. It is shown that the introduction of 1-, 2- and 4-wt.% polyvinyl alcohol (PVA) as a binder in an alumina suspension leads to the formation of irregular granules. Depending on atomization conditions, spherical, “tadpole-like,” granule-satellite and granule aggregates may form during SFD. Increasing the flight time of droplets before the fixing of their shape when they come in contact with liquid nitrogen effectively contributes to the spheroidization of alumina granules. Compacting PVA-free SFD granules leads to the formation of diagonal flaws in a green-body structure. Adding PVA prevents the abovementioned defects by increasing the strength of alumina granules. Increasing the amount of PVA leads to an increase in “tadpole-like” granule content and, consequently, a decrease in a green-body density.     

微波加热在纱线烘干中的应用

介绍了微波加热的基本原理、特点以及影响微波加热的因素,与蒸汽烘干、射频烘干相比,微波加热比蒸汽烘干节能40％,比射频烘干节能20％,仅每年运营维护费用比射频烘干节省4．5万元。提出应重点加强微波与物料间相互作用理论、微波场中物料的传热、传质机制,微波加热工艺与设备、微波加热技术与其它技术的有机结合等方面的研究。     

Spray and freeze drying of human milk on the retention of immunoglobulins (IgA,IgG, IgM)

Several freeze-drying and spray-drying methods were investigated in relation to the retention of immunoglobulins (Ig) A, IgG, and IgM. Spray drying produced human milk powders with 2% humidity and a good retention of IgG (>88%) and IgM (～70%). However, only 38% of IgA remained after spray drying. For freeze drying, only the highest heating plate temperature used in this study (40°C) brought IgA content down to 55% in powder with 1.75% residual humidity, whereas milk samples undergoing lower temperatures had higher preservation rates (75% for IgA and 80% for IgG and IgM) and higher residual moisture contents. From these results, it can be concluded that IgA is the most sensitive Ig lost during drying processing of human milk. The best method to generate human milk powders without a significant loss of Ig was thus freeze drying at 30°C heating plate temperature, which accelerated the process compared to lower processing temperatures, but still had good overall Ig retention.     

冻干魔芋胶性能的实验研究

介绍了采用冻干工艺获取的优质魔芋胶（KGM）的主要性能及其实验研究。该工艺方法具有成胶薄、韧性好、保存容易而且时间长、复水性好等优点。魔芋胶可广泛用于食品保鲜与储藏以及保健、医疗等方面；由于它价格低，可进一步拓展其应用领域，深受医疗保健人员的关注。     

Effect of three drying methods on the drying characteristics and quality of okra

The objective of this study was to compare the drying characteristics and quality of dried okra obtained by vacuum freeze drying (VFD), microwave vacuum drying (MVD), and pulse-spouted microwave vacuum drying (PSMVD). The quality parameters include color (L*, a*, and b*), texture (hardness and fracturability), shrinkage ratio (SR), nutrient retention (chlorophyll, flavonoids, and vitamin C), and sensory score was investigated. Vacuum freeze drying maximally preserved the original properties of samples. And the samples dried by PSMVD showed higher quality and more uniformity compared to MVD. Considering of all aspects comprehensively, such as cost-effectiveness, practicability, and scale-up, PSMVD was a promising technique which would match results obtained by vacuum freeze drying.