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The chapters in this volume explore ultrasound-assisted regeneration of silica gel, ultrasound-assisted regeneration for a new honeycomb desiccant material, ultrasound-atomizing regeneration for liquid desiccants, ultrasonic transducers, and much more.

Over the last few decades, many researchers have investigated in detail the characteristics of bioactive compounds such as polyphenols, vitamins, flavonoids, and glycosides, and volatile compounds in fruits, vegetables and medicinal and aromatic plants that possess beneficial properties, as well as consumer acceptance and preference. The main aim of this article is to provide an updated overview of recent research endeavors related to the effects of the drying process on the major bioactive/effective compounds in agricultural products. Particular emphasis was placed on details related to the changes occurring in vitamin C, polyphenols, flavonoids, glycosides and volatile compounds, as well as the antioxidant activity. An analysis of the degradation mechanisms of these compounds showed that vitamin C, phenols, flavonoids and glycosides react with oxygen during the convective drying process under high drying temperatures, and the reaction rate results in degradation in such bioactive compounds due to high reducibility. On the other hand, high temperature results in a short drying time, thus minimizing the degradation of bioactive compounds. The reviewed research works addressing this trend revealed that the ideal drying temperatures for retaining vitamin C, polyphenols, flavonoids, glycosides, volatile compounds and their antioxidant activity were 50–60 °C, 55–60 °C, 60–70 °C, 45–50 °C, 40–50 °C and 50–70 °C, respectively. In conclusion, to maintain plant bioactive components, convective drying at relatively low drying temperatures is strongly recommended.

In the absence of effective drying techniques, a lot of food gets wasted as there is a lack of post-harvest processes. In India, most of the agricultural produces like paddy, maize, wheat, corn, oil seeds, pulses, chillies, etc. require a temperature range of 50–80 °C for effective drying. Hence, in these conditions, solar drying techniques seem to be the most economical; also, it is safe and eco-friendly. Various types of solar dryers are used across India and worldwide; these are direct solar dryer, green house dryer and indirect solar dryer. Nowadays, indirect type solar dryers are most commonly used because of their several advantages over direct solar dryers. In case of indirect type solar dryers, the products to be dried are kept inside a separate compartment known as drying chamber. Hot air is obtained from the solar collectors either by direct heating method or by using a secondary heating medium and then supplied to the drying chamber for heating of the products. This paper presents a detailed review of various innovative designs of indirect type solar dryers and compares the performance of different types of dryer configuration in terms of collector efficiency, dryer efficiency, drying time and maximum air temperature. Also, the effects of various operating parameters on the thermal performance of such dryers have been discussed.

Drying is considered as the most common and fundamental technique for the postharvest preservation of herbs and is regarded as a good process to retain bioactive compounds. Past studies suggest that the choice of drying method and the parameters applied were able to influence the chemical and biological activities of herbs because pronounced differences in chemical content and composition were observed between the different drying methods. This has warranted numerous studies over the years to determine the influence of various drying methods on the content of bioactive compounds in functional food. However, reviews on the impact of drying on the bioactivity of dried herbs are rather scarce. Additionally, the influence of drying methods on the antibacterial activity of herbs has yet to be reviewed. Therefore, this paper attempts to provide a critical review on the influence of current drying process technology on the antibacterial and antioxidant properties, as well as the essential oil content, of various herbs. The use of innovative, new or existing drying technologies in preserving the active compounds was included in this paper. It was found that (i) no single drying method can be effectively used for the dehydration of all herbs; (ii) heat treatment can lead to biochemical changes (Maillard reaction), which increases the antibacterial activity; and (iii) innovative combined drying methods are promising in the production of herbs with high antioxidant activity and higher yields of total volatile concentrations.

Desiccants play vital roles in dehumidification and atmospheric water harvesting; however, current desiccants have mediocre hygroscopicity, limited recyclability, and high energy consumption. Herein, we report a wood-inspired moisture pump based on electrospun nanofibrous membrane for solar-driven continuous indoor dehumidification. The developed moisture pump with multilayer wood-like cellular networks and interconnected open channels is composed of a desiccant layer and a photothermal layer. The desiccant layer exhibits an unprecedented moisture absorption capacity of 3.01 g g −1 at 90% relative humidity (RH), fast moisture absorption and transport rates, enabling atmospheric water harvesting. The photothermal layer shows a high solar absorption of 93%, efficient solar thermal conversion, and good moisture permeability, thus promoting water evaporation. The moisture pump efficiently reduces the indoor relative humidity to a comfort level (40‒60% RH) under one-sun illumination. This work opens the way to develop new-generation, high-performance nanofibrous membrane-based desiccants for energy-efficient humidity control and atmospheric water harvesting. Desiccants are important for dehumidification, but application is hindered by limited hygroscopicity, recyclability, and energy efficiency. Here, the authors report a moisture pump comprised of an electrospun nanofibrous memebrane for solar-driven continuous indoor dehumidification.

Two different drying methods (vacuum freeze-drying and hot-air drying) were used to dry mulberry of three varieties ’Baiyuwang’(D1), ’Longsang’(D2) and ’Zhongshen.1’(D3), and the fresh fruit of each variety was used as the control. The effects of different processing conditions on the physical characteristics, nutrients, functional components and antioxidant activity of mulberry fruit were analyzed. The results show that after different drying methods, after vacuum freeze-drying, the physical properties of dried mulberry fruit such as wettability, hygroscopic property and water retention, soluble protein, ascorbic acid and other nutrients, functional components such as polyphenols, resveratrol, chlorogenic acid and anthocyanin, and antioxidant activities such as DPPH free radical scavenging ability and ABTS free radical scavenging ability were superior to hot air drying (P < 0.01). It was concluded that vacuum freeze drying was more beneficial for retaining the original quality of mulberry than hot air drying. This study can provide a retaining theoretical basis for mulberry deep processing and comprehensive development and utilization.

Process of grain drying is discussed by the authors, which is considered one of the preliminary stages in the technology of biodiesel production. The drying process has a number of disadvantages that affect the quality and cost of biodiesel fuel. The impossibility of uniform heating and maintaining the required temperature with minimal energy costs is considered one of the most important defects that deserve scientific research. The authors propose a method for changing the heating system and preheating raw materials, based on world experience. We carried out mathematical calculations, provided the change in the temperature field of the drying chamber over time, and we also performed industrial experiment. Based on our results we determined the optimal number of heating sources of raw materials, taking into account the dimensions of the drying chamber. The authors propose a technical solution with which a uniform temperature field can be obtained in the drying chamber. Thus, the uniformity of the chamber heating will be increased, and large operating costs associated with leakage of oil from the grains will be disappeared.

Water content has a pronounced influence on the properties of rock materials, which is responsible for many rock engineering hazards, such as landslides and karst collapse. Meanwhile, water injection is also used for the prevention of some engineering disasters like rock-bursts. To comprehensively investigate the effect of water content on mechanical properties of rocks, laboratory tests were carried out on sandstone specimens with different water contents in both saturation and drying processes. The Nuclear Magnetic Resonance technique was applied to study the water distribution in specimens with variation of water contents. The servo-controlled rock mechanics testing machine and Split Hopkinson Pressure Bar technique were used to conduct both compressive and tensile tests on sandstone specimens with different water contents. From the laboratory tests, reductions of the compressive and tensile strength of sandstone under static and dynamic states in different saturation processes were observed. In the drying process, all of the saturated specimens could basically regain their mechanical properties and recover its strength as in the dry state. However, for partially saturated specimens in the saturation and drying processes, the tensile strength of specimens with the same water content was different, which could be related to different water distributions in specimens.

The possible health advantages and abundance of physiologically active substances in mushrooms make them a prized food. To preserve mushrooms and extend their shelf life, drying is a commonly used method. This paper seeks to investigate various mushroom drying methods and analyze their impact on the physicochemical properties of mushrooms. When mushrooms are dried, the chemical and physical characteristics of the product change, potentially losing nutrients and changing in texture and flavor. To ascertain their effect on the quality of the mushrooms, it is crucial to research the various drying systems. The goal of this review is to analyze and assess the various drying methods for mushrooms, namely, solar drying, hot air drying, microwave drying, infrared drying, vacuum drying, osmotic drying, ultrasound-assisted drying, freeze drying, and electrohydrodynamic drying. The article also attempts to examine how these techniques affect the physicochemical properties of mushrooms that have been identified by numerous studies. According to the records, freeze-dried mushrooms exhibited superior preservation of texture and higher levels of antioxidants compared to hot air-dried and sun-dried mushrooms. On the other hand, microwave-dried mushrooms had greater amounts of total phenolic compounds and antioxidant activity but lower levels of vitamin C compared to hot air-dried mushrooms. Therefore, it is essential to consider the impact of the drying method on the nutritional and sensory properties of the mushrooms to ensure that the final product meets the desired standards.

The microstructural evolution of loess had a significant impact on the collapsibility of loess during wetting-drying cycles. Based on the analysis of scanning electron microscope (SEM) images by using Image-Pro Plus, the present study quantitatively compared the microstructural parameters of original loess and remoulded loess with different moisture content before and after wetting-drying cycles in size, shape, and arrangement. In size, the average diameter of both original loess particles and remoulded loess particles increased with the increasing of initial moisture content. However, the average diameter of original loess particles was slightly larger than that of remoulded loess particles before wetting-drying cycles. In contrast, the average diameter of both original loess particles and remoulded loess particles were very close to each other after three wetting-drying cycles. In shape, before wetting-drying cycles, the average shape factor of original loess particles was higher than that of remoulded loess particles. After three wetting-drying cycles, the difference in the average shape factor of both two loess samples with 5% initial moisture content is similar to that before wetting-drying cycles. Nevertheless, the average shape factor of both original loess particles and remouled loess particles with 15% initial moisture content were very close to that with 25% initial moisture content. In the arrangement, directional frequency indicated remoulded loess appeared to be more vertically aligned than original before and after three wetting-drying cycles. Furthermore, the directed anisotropy rate of remoulded loess was higher than that of the original loess before and after three wetting-drying cycles. In summary, the size, shape, and arrangement of both original loess particles and remoulded loess particles varied in different degrees before and after three wetting-drying cycles. Combined with the water retention curve of the loess, we analyzed the microstructural evolution mechanism of two loess particles during wetting-drying cycles. It is an excellent significance to study the engineering properties of original loess and remoulded loess.