Effect of freeze dried,hot air dried and fresh onions on the composition of volatile sulfocompounds in onion oils

The bioactivity of onion, particularly its oil, has gained increasing research attention. Preparation of onion oil is challenging due to its low oil content and abundance of water. In this study, pilot-scale drying combined with laboratory extraction was conducted for sample preparation. GC/MS and solid phase microextraction (SPME) analyses were performed to evaluate the correlation between onion oil and drying. Results showed that drying significantly influenced the sulfocompounds composition of onion oils. Dipropyl disulfide and dispropyl trisulfide were the most abundant compounds in fresh onions (accounting for 68.41% to 93.13% of the total volatile sulfocompounds). The total contents of sulfocompounds in vacuum freeze dried and hot air dried onion powder were 4.96% and 39.79%, respectively, which account for 24.59% to 48.89% of the total content. Dimethyl sulfides and thiophenes were the main compounds in the onion oils. The highest content of sulfocompounds was obtained in the oil of hot air dried powder. Pilot-scale hot air drying was the optimal pretreatment method for onion oil extraction. It enjoys lower energy lost, shorter process time, and higher quality of the oil compared with freeze drying. The results may be helpful for onion oil production and bioactivity evaluation.     

Dehydration of Concentrated Ganoderma lucidum Extraction by Combined Microwave-Vacuum and Conventional Vacuum Drying

Combination of microwave-vacuum drying and conventional vacuum drying was investigated as a potential method for drying concentrated Ganoderma lucidum extraction. The Ganoderma lucidum was extracted by hot water (60-65°C) and then concentrated to moisture of about 70% (wet basis) in a rising-film evaporator. The concentrated sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional vacuum drying at the temperature of 55-60°C to final moisture content about 6% (wet basis). The retention of polysaccharide and triterpenes of Ganoderma lucidum dried by this method were evaluated and compared with those dried by freeze drying and conventional vacuum drying alone. The comparison showed that the quality of extraction dried by the current method was close to that of freeze-dried extraction and much better than that of conventional vacuum-dried ones.     

Dehydration of Concentrated Ganoderma lucidum Extraction by Combined Microwave-Vacuum and Conventional Vacuum Drying

Combination of microwave-vacuum drying and conventional vacuum drying was investigated as a potential method for drying concentrated Ganoderma lucidum extraction. The Ganoderma lucidum was extracted by hot water (60–65°C) and then concentrated to moisture of about 70% (wet basis) in a rising-film evaporator. The concentrated sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional vacuum drying at the temperature of 55–60°C to final moisture content about 6% (wet basis). The retention of polysaccharide and triterpenes of Ganoderma lucidum dried by this method were evaluated and compared with those dried by freeze drying and conventional vacuum drying alone. The comparison showed that the quality of extraction dried by the current method was close to that of freeze-dried extraction and much better than that of conventional vacuum-dried ones.     

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.     

Effect of Calcium Ion and Microwave Power on Structural and Quality Changes in Drying of Apple Slices

Effects of impregnated calcium ion and microwave (MW) power on texture, rehydration, shrinkage, color, and other selected indexes of freeze-dried apple slices were investigated. Apple slices were dried by freeze drying and microwave freeze drying (MFD) separately. Vacuum impregnated (VI) and non-vacuum-impregnated apple slices were dried at various microwave power levels. Non-vacuum-impregnated apple slices were found to preserve their mechanical structure better than the VI-treated ones. Microwave application resulted in decreased protopectin fraction as well as total pectin content. As microwave power varied from 1.2 to 2.0 W/g, the total pectin content decreased from 0.810 to 0.521 (expressed as g galacturonic acid/100 g fresh sample). The effect of microwave power in decreasing the drying time was significant. The color of MFD apple slices varied to a minor extent with MW power level over the range of parameters studied.     

Effect of Different Drying Methods on the Microwave Extraction of Phenolic Components and Antioxidant Activity of Highbush Blueberry Leaves

In the last few decades, researchers have found blueberry leaves to be an interesting source of different phenolic compounds, and drying is an important part of their postharvest and sample preparation processes. In the current study, blueberry leaves were dried using microwave-assisted hot air drying or hot air drying alone at 45, 60, and 75°C to 10–15% wet basis. Corresponding drying characteristics were determined by fitting the moisture ratio obtained in each case with eight theoretical and semitheoretical models for hot air and microwave drying stages. It was observed that best fitting drying models for blueberry leaves depended not only on the nature of the biomaterial but also on the method of drying and the temperature of drying. Phenolic content, monomeric anthocyanin content, and the corresponding antioxidant activity in terms of 2,2-diphenyl-1-picrylhydrazyl (DPPH) inhibition activity and ferric reducing ability of plasma (FRAP) activity were evaluated for the leaf extract obtained following microwave extraction of the dried samples obtained using the above-mentioned drying methods and were compared to the corresponding bioactive compositional characteristics of freeze-dried blueberry leaves. It was observed that the freeze-dried sample had the highest content of total phenolics and total monomeric anthocyanins along with high antioxidant activity. Furthermore, extracts obtained from the microwave-dried leaf samples obtained with a drying temperature of 60°C had highest total phenolic content and highest total monomeric anthocyanin content among all other drying methods and the extract had an antioxidant activity similar to the freeze-dried blueberry leaf samples, implying that microwave drying at 60°C is a potential alternative to freeze drying for preservation of the phenolic components and antioxidant activity of dried blueberry leaves.     

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 Spouted Bed Drying of Lettuce Cubes

Microwave-assisted spouted bed (MSBD) drying of lettuce cubes was investigated experimentally. Response surface methodology was used to optimize the process with spouting air temperature, microwave power level, and superficial air velocity. The dried product obtained was compared with that obtained using other drying technologies such as hot air drying, air spouted bed drying, vacuum microwave drying, and vacuum freeze drying. The comparison is based on the rehydration ratio, chlorophyll content of the product, color, and the drying time required.     

Freeze Drying of Apple Slices with and without Application of Microwaves

In this study, Fuji apple slices were dehydrated using freeze drying (FD) combined with microwave assisted with vacuum drying (VMD). The optimal parameter for the diversion point of moisture content from FD to VMD process was at the moisture level of 21%, and for VMD the optimal parameter for vacuum pressure was at 9.15 kPa and microwave power density was at a level of 3.18 w/g. The results show that the two-step technique can significantly reduce total FD time required by up to 40%, while the nutritional value of the dried apple chips remained unchanged compared to FD used alone.     

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。     

Vacuum Drying for Ultrafine Alumina Powders

It is well known that the drying of liquid-borne powders will create agglomerates and the problem of agglomeration is particularly acute in the nanoscale range. To eliminate/mitigate the agglomeration problem, in this study, a vacuum drying technique was used for drying the colloid solution with θ-Al₂O₃ ultrafine particles. For comparison purposes, other drying methods including oven drying, microwave drying, and freeze drying were also applied for drying of the same kind of colloid solution. The results indicate that the redispersibility, which is closely related to the degree of agglomeration, of the dried powders obtained from vacuum drying is better than that obtained from freeze drying. More surprisingly, results showed that the dried powders obtained from the vacuum drying assisted by microwave heating has the redispersibility close to 100%.     

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.     

Effect of Drying Methods on the Quality of the Essential Oil of Spearmint Leaves (Mentha spicata L.)

Drying is one of the primary processes involved in the manufacture of herbs, which themselves come in the form of stems, leaves, and roots. The quality of the final product depends on the procedure used and drying method. This article presents the results pertaining to the drying behavior of spearmint in both hot air drying and freeze drying conditions. Conventionally, herbs are dried at high temperatures (40–45°C), which results in a deterioration of product quality. The characteristics of vacuum freeze–dried herbs were studied, and the quality of the freeze-dried products was assessed. It was found that drying time and essential oil content were strongly influenced by chamber pressure. Higher chamber pressure tended to lengthen the drying time but preserved the major volatile compounds of spearmint in the final product. The quality of the freeze-dried product was assessed as being lower than that of the raw material but higher than that of a convectively dried product. Four different mathematical models were fitted to the drying data. A water absorption test confirmed that the rehydration ratios of vacuum freeze–dried mint leaves were higher than those that were convectively dried.     

Drying Characteristics and Quality of Restructured Wild Cabbage Chips Processed Using Different Drying Methods

The drying characteristics of restructured wild cabbage chips dried using microwave vacuum (MVD), hot air (AD), and microwave freeze drying (MFD) were compared. Some of the key quality parameters of restructured wild cabbage chips such as fracturability and color and sensory characteristics were measured. Results showed that the drying time was reduced with the increase of microwave power (MVD/MFD) and in the case of air drying by the temperature (AD). Drying time was the shortest in the MVD process. Optimal quality of dried chips was obtained with the MFD process at a microwave power level 2.0 W/g.     

Drying kinetics and product quality of green soybean under different microwave drying methods

The objective of this study was to investigate the effect of different microwave drying techniques on the drying kinetics and product quality of dried green soybean. Experiments were conducted using microwave vacuum drying (MVD), pulse-spouted vacuum microwave drying (PSMVD), pulse-spouted microwave drying (PSMD), and microwave freeze drying (MFD). Parameters of apparent density, color, processing temperature, expansion ratio, rehydration ratio, texture, and microstructure of the dried products were determined. The results showed that the MFD green soybean had a small change on bright color, compared with the fresh samples, but the drying time was the longest among the four methods. The bright color value of PSMVD/PSMD/MVD, respectively, was 79.77, 71.43, and 55.45, and drying time of them was slightly different. The PSMVD/PSMD showed advantages over MVD by improving the product quality.     

Study of drying kinetics of salmon processing by-products at different temperatures and the quality of extracted fish oil

Samples of salmon processing by-products were minced, mixed, and partially dried to moisture content of 90?±?5% (dry basis), at two different temperatures 60 and 100°C (using hot air-drying and oven-drying, respectively). Theoretical and semitheoretical drying models were used for modeling of the drying kinetics of salmon by-products mix, where Page model and logarithmic models were observed as the best models presenting the drying kinetics of salmon by-products at 60 and 100°C, respectively. Salmon by-product oil was extracted from the partially dried by-product through centrifugation and was compared with enzymatically extracted (enzymatic extraction method was considered as the control method) salmon oil, in terms of fatty acid profile of the oils. The oil content obtained through semidried samples and enzymatically treated samples ranged between 16.234 and 18.212?g/100?g of fresh sample, which were not significantly different. The fatty acid composition was similar in all the cases. The fatty acids predominantly observed in the salmon oils included oleic acid, linoleic acid, and palmitic acid. Other fatty acids included palmitoleic acid, stearic acid, vaccenic acid, gondoic acid, and myristic acid. Docosahexaenoic acid and eicosapentaenoic acid contents were between 1 and 2% of the oil extracted in all the cases, and DPA (Docosapentaenoic acid) content was approximately 1%. Hence, partial dehydration at both the temperatures was concluded as a potential processing method for increasing the storability of salmon by-products and obtaining salmon oil with high quality.     

Antioxidant potential of atmospheric freeze-dried apples as affected by ultrasound application and sample surface

ABSTRACT

Atmospheric freeze drying (AFD) yields products of a similar quality to the conventional vacuum freeze-drying technique, but reduces the operating cost. However, it involves very low drying rates. The sample surface/mass ratio is one of the process variables that can be taken into account to reduce drying time. Moreover, power ultrasound (US) can also be used to intensify this process because of its effects on external and internal mass transfer resistance. However, both factors may affect not only the drying time but also the final product quality. Therefore, the aim of this study was to address the influence of both ultrasound application and the sample surface/mass ratio on the drying process and the antioxidant potential of atmospheric freeze-dried apple. For that purpose, two sample geometries with different surface/mass ratio were considered: slabs (30?×?30?×?10?mm³) and cylinders (diameter: 9?mm and height: 30?mm). The samples were freeze dried (?10°C) with ultrasound application (21.7?kHz) at different power levels (0, 10.3, 20.5, and 30.8?kW/m³). The total phenolic content (TPC), antioxidant capacity (AC), and ascorbic acid content (AA) were measured in the dried apple. The drying time was significantly shorter for cylindrical samples than for slabs, probably due to their higher surface/mass ratio. The application of US increased the drying rate, this increase being greater for the slab than for the cylindrical particles used in this study. In general, AFD reduced the TPC, AC, and AA, the final content being significantly greater for slabs than for cylinders. This fact can also be related to the lower surface/mass ratio in the case of slabs. US application further reduced TPC, AC, and AA content, probably due to some cellular damage produced by the acoustic waves and to the oxygen transfer improvement. Nevertheless, the bigger particles (slabs) dried with ultrasound needed a 10% of drying time than the smaller ones (cylinders) dried without ultrasound. Moreover both kind of samples presented similar antioxidant potential.     

Effects of Microwave Drying on Lipid Oxidation of Stuffed Pasta

The aim of this work was to evaluate and compare the effects of conventional (hot air) and microwave drying on the lipid oxidation of stuffed pasta. Experiments were carried out on the pasta type ravioli dried by conventional and microwave treatments. Peroxide values and induction times were evaluated for the oil extracted from the stuffing. Peroxide values of the lipid extracts for the samples dried by conventional drying and microwave drying were similar (P-level = 0.51) and less than threshold acceptable value (25 mequiv O₂/kg oil). The use of microwave processing could be a remarkable energy saving measure as well as a way of lowering production costs without compromising product quality.     

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。     

Effect of different drying methods on zein-based microcapsules loaded with Artemisia argyis essence obtained by anti-solvent precipitation

Microencapsulation is considered an efficient technique to protect functional materials from oxidization while enabling controlled release. In this study, anti-solvent precipitation was used to prepare zein-based microcapsules loaded with Artemisia argyis essence (AAE@ZMs). The impact of different drying methods, namely vacuum drying, freeze drying, and spray drying on AAE@ZMs was evaluated. Quality of AAE@ZMs was evaluated by the determination of color, moisture content, bulk density, chemical structure, and morphology evaluation. Freeze dried AAE@ZMs (F-AAE@ZMs) and vacuum dried microcapsules (V-AAE@ZMs) respectively showed stronger water and oil absorption capacities. The residual content of Artemisia argyis essence (AAE) in V-AAE@ZMs was higher than those in F-AAE@ZMs and spray dried microcapsules (S-AAE@ZMs) after continuously releasing for 120 h. Meanwhile, heated from 30 to 600°C, the residues of V-AAE@ZMs and F-AAE@ZMs were lower than those of S-AAE@ZMs. Therefore, drying methods greatly affected key quality parameters of AAE@ZMs. This study provides guidance on the use of drying methods in microcapsules delivery systems with zein or other materials.