Search Results (68)

Opportunities to capture anticipated niche markets for diverse populations continue to rise. Okra (Abelmoschus esculentus L.), considered a high-value crop, is rich in nutritional and medicinal properties; however, fresh okra is highly perishable. This study examined the effects of thermal pre-treatments and drying processes in combination on the nutritional quality of dried okra. The experiment consisted of two thermal treatments (steam-blanched and hot water-blanched, and the control) and three drying treatments (freeze-dried, hot air-dried, and infrared-dried). Okra was grown in black plastic mulch, harvested twice per week, and processed three times throughout the growing season. The study analyzed moisture content, water activity, phytonutrients, ascorbic acid, β-carotene, and antioxidant activities. No significant differences were observed in moisture content and water activity among the treatments. Significant differences were observed among treatments and harvest time for total phenolic and flavonoid contents and antioxidant activity. Notable differences in β-carotene content were observed across all treatments. Based on the findings, the steam-blanched freeze-dried treatment was the most effective preservation technique for maintaining the nutritional and functional quality of dried okra. Hot water-blanching, hot air-drying, and infrared-drying were the least effective for the development of a high-value, nutrient-dense dried okra value-added product. Full article

Drying is a crucial postharvest preservation step, particularly for fruits and vegetables, due to their high moisture content. Physical, sensory, and storage qualities after drying are of interest to food engineers; however, for medicinal purposes, such as nutraceuticals or functional foods, the retention of pharmacological or bioactive compounds is of great interest. This review discusses conventional novel/modern drying technologies and their impact on pharmacological compounds of MEFVs. Conventional drying techniques (sun drying and hot air drying) are cost-effective but slow and usually induce significant losses of thermolabile pharmacological compounds. In contrast, novel/modern drying techniques (solar drying, vacuum drying, freeze drying, microwave drying, infrared drying, heat pump, refractance window, and electrohydrodynamic drying) can accelerate faster moisture removal, but their impact on the pharmacological compounds varies. Current trends in drying research emphasize process optimization, technology hybridization, pretreatment methods, real-time monitoring, and green energy integration to enhance pharmacological compound retention while ensuring sustainability. Full article

Alfalfa, as a high-quality forage crop, undergoes a drying process that is critical to its product quality and commercial value. This paper systematically reviews research progress on alfalfa drying technologies and equipment throughout the entire process. First, it proposes a comprehensive production technology model covering three core stages: drying pretreatment, drying conditioning and optimization, and product quality control. This model emphasizes adaptability to material characteristics, processing methods, product quality, and economic efficiency. Second, it delves into the drying mechanisms of alfalfa, detailing the forms of water presence (free water or bound water), migration pathways, and the three-stage water loss periods: constant rate, first falling rate, and second falling rate. It identifies “asynchronous drying of stems and leaves” as the core issue causing nutrient loss and technical challenges. Subsequently, a comprehensive review was conducted on pre-treatment equipment such as mowing and flattening, as well as various drying methods including natural drying, hot-air drying, solar drying, and microwave drying. The principles, characteristics, and impacts of these methods on alfalfa quality were evaluated. Additionally, a comprehensive quality assessment system for alfalfa hay was summarized, incorporating physical, chemical, and biological methods. Finally, future development directions are proposed: developing domestically produced, intelligent drying equipment; integrating clean energy to reduce energy consumption; and achieving precise control of drying processes through establishing multi-scale heat and mass transfer models. These efforts will advance China’s alfalfa drying industry toward standardization, integration, and intelligence, ensuring a stable supply of high-quality hay. Full article

Oranges are popular worldwide, due not only to their refreshing taste but also to their high content of bioactive compounds. The main phytochemicals in oranges are phenolic compounds, vitamins, and carotenoids, which contribute to their antioxidant and anti-cancer activities. Various drying methods are used to remove the high moisture content in orange products to extend their shelf life. This review summarizes and compares the effects of different drying methods such as hot air drying, freeze drying, vacuum drying, spray drying, microwave drying, solar drying and innovative pretreatment on the physicochemical quality of orange products including slices, peels, and by-products. It lists the key parameters, advantages, and disadvantages of drying methods, as well as a decision tree for “product type-constraints-recommended drying method with pretreatment”. For example, the results indicate that vacuum microwave drying is effective in drying orange slices, and control techniques are employed to assist the drying process. Freeze drying preserves more phytochemicals in orange peels and their by-products, which results in higher antioxidant activity. Pretreatments like pulsed electric field and ozone enhance drying efficiency and phytochemical retention. Different drying methods are adopted to treat different by-products. This work can be used as a guide for selecting the optimal drying technique to balance efficiency, nutritional quality, and industrial scalability for different orange products. Full article

In this study, the effects of non-thermal pretreatment such as corona discharge plasma (CDP-21 kV), dielectric barrier discharge plasma (DBDP-32 kV), and ultrasonic waves of different powers (US-180 W, 210 W, 240 W) on hot-air drying of ferruginous yam were compared. The regulatory effects of ultrasonic and cold plasma pretreatment on the drying characteristics and quality of yam were systematically evaluated by determining the drying kinetic parameters, physicochemical indexes, volatile components, and energy consumption. The results showed that ultrasonic pretreatment significantly improved the drying performance of yam compared with different cold plasma treatments, with the highest drying rate and effective moisture diffusion coefficient in the US-180 W group. In terms of quality, this treatment group exhibited better color retention, higher total phenol content (366 mg/100 g) and antioxidant activity, and optimal rehydration performance. Low-field nuclear magnetic resonance (NMR) analyses showed a more homogeneous water distribution, and gas chromatography–mass spectrometry (GC-MS) identified 55 volatile components. This study confirms that the US-180 W ultrasonic pretreatment technology can effectively improve the drying efficiency and product quality of yam and at the same time reduce the energy consumption. The results of this study provide a practical solution for the optimization of a process that can be replicated in the food drying industry. Full article

This study aimed to evaluate the drying kinetics, microstructural features, moisture content, color, pH, aw, texture, acidity, rehydration capacity, and sensorial attributes of strawberry slices processed by different drying methodologies. Strawberry samples were processed by hot air-drying (HA, 60 °C, 0.5 m/s), freeze-drying (FD, 0.055 mbar), and pulsed electric field (PEF)-assisted freeze-drying (PEFFD, 1 kV/cm and 3.2 kJ/kg). PEF pre-treatment significantly increased cell membrane permeability by forming micropores, which led to a significant reduction in the moisture content of up to 8.87% and improved the drying efficiency. Nonetheless, this pre-treatment did not significantly alter the drying rate due to the inherent constraints of the freeze-drying process. PEFFD samples better retained their shape, volume, and visual quality, and exhibited a maximum rehydration capacity of 64.90%. The ascorbic acid retention was found to be higher in the FD and PEFFD when compared to HA. FD and PEFFD samples had an increase in both red and yellow hue. PEF shows promise as a pre-treatment technique, improving both the drying efficiency and strawberry quality. Further studies are needed to assess PEFFD’s industrial scalability and economic feasibility. Full article

This study investigates the effects of electric field pretreatment parameters such as electric field strength (0.1–0.2 kV/cm), waveform (sinusoidal vs. square), and application mode (continuous vs. pulsed) on the quality attributes of dried Fuji apple slices, including ascorbic acid (vitamin C) retention, β-carotene content, and hydroxymethylfurfural (HMF) formation. Electric-field-treated samples were compared to untreated controls after convective drying at 75 °C. Results revealed that vitamin C was significantly influenced by waveform, with sinusoidal waves preserving about 27% more vitamin C than square waves, likely due to reduced oxidative degradation from gentler electroporation. Conversely, square waves caused the highest β-carotene losses (25% vs. control), attributed to prolonged peak voltage destabilizing carotenoids. HMF formation was reduced by 10–23% in electric-field-treated samples compared to controls, linked to accelerated drying rates limiting Maillard reaction time. Low electric field strengths (0.1–0.15 kV/cm) enhanced antioxidant activity; however, higher intensities showed a potential decline. The square waveform had a more detrimental effect on phenolic compounds than the sinusoidal waveform. These findings suggest that low electric field pretreatment, particularly with sinusoidal waveforms at 0.2 kV/cm, enhances drying efficiency while balancing nutrient retention and HMF mitigation, offering a promising strategy for producing high-quality dried fruits. Full article

This study aimed to investigate the impact of ultrasonic pretreatment vacuum drying (UAVD) and temperature on drying kinetics and qualitative attributes of blood oranges in comparison to several drying methods: hot air drying (HAD), vacuum drying (VD), and freeze drying (FD). The drying kinetics and modeling, total phenolic content (TPC), antioxidant capability (assessed using DPPH and ABTS tests), individual phenolic profiles, vitamin C concentration, and color factors were meticulously examined. Drying times were recorded as 22.5 h, 12.5 h, and 9 h for HAD; 11.5 h, 9.5 h, and 8.5 h for VD; and 10 h, 8.5 h, and 7.5 h for UAVD at 50, 60, and 70 °C, respectively. The HAD, VD, and UAVD procedures were conducted at 50, 60, and 70 °C, resulting in reduced drying periods with increasing temperature. The integration of ultrasound markedly lowered drying durations. Eleven thin-layer drying models were utilized to recreate the drying process precisely. The D_eff values of the HAD, VD, and UAVD dried samples varied from 9.08 × 10⁻⁶ to 2.82 × 10⁻⁵ m²/s, from 2.60 × 10⁻⁵ to 2.96 × 10⁻⁵ m²/s, and from 2.20 × 10⁻⁵ to 2.99 × 10⁻⁵, respectively. Among the desiccated blood orange slices, the greatest total phenolic content (TPC) was observed in freeze-dried samples (131.27 mg GAE/100 g), followed by those dried using ultrasonic-assisted vacuum drying (UAVD) at 50 °C (128.77 mg GAE/g DM). Dried blood orange slices had a vitamin C content of 29.79 to 49.01 mg/100. The drying process substantially impacted the color parameters L*, a*, and b*. These findings highlight the efficacy of ultrasound-assisted drying in decreasing drying duration while improving the retention of bioactive components in blood orange slices. Full article

The seasonality of Diospyros kaki limits its consumption, making it increasingly necessary to develop products that allow it to be available all year round. Therefore, the aim of this study was to optimize the osmotic dehydration process and to evaluate the changes in the physico-chemical, bioactive and volatile composition of persimmon subjected to drying. A central composite rotatable design was used with the independent variables as sucrose concentration (%) and immersion time (min). The desirability function for sucrose solution concentration and immersion time was 29.5% for 60 min for hot air oven drying and 38% for 29 min for freeze drying. The dehydrated fruit treated with osmotic pretreatment showed better responses in the quantification of bioactive compounds and retention of volatile compounds. Compounds such as nonanal and 6-methyl-5-hepten-2-one were identified in all the dehydrated products and the OD had a positive influence on their retention, especially for the lyophilized samples. Thus, it is clear that osmotic pretreatment is an ally in protecting the physico-chemical and chemical characteristics of the fruit when it undergoes a drying process, especially with regard to bioactive and volatile compounds. Full article

Ultrasound (US) is a non-thermal food processing method that can be used as a pre-treatment or integrated during drying to enhance mass transfer by inducing cavitation and forming microchannels in plant tissue. Thus, this study investigated the combined effect of ultrasound pre-treatment (21 kHz; 180 W; 10 min, 20 min, 30 min) and the subsequent hybrid drying process—ultrasound-assisted hot-air drying (temperature of 70 °C, frequency of 36 kHz; ultrasound power of 120 W, 160 W, 200 W)—on the drying kinetics and quality attributes of dried Gloster apples. The experimental design was optimized using the response surface methodology (RSM). The effects of ultrasound parameters on drying time, dry matter content, water activity, rehydration and hygroscopic properties, color change, textural properties, content of vitamin C, polyphenols and flavonoids, and antioxidant activity were evaluated. Among the analyzed variants, the most effective combinations were longer US duration (30 min) with lower US power (120 W) or shorter US duration (10 min) with higher US power (200 W). To obtain dried material with the most desirable rehydration and hygroscopic properties, a US power in the range of 120–160 W, preceded by a US pre-treatment lasting 20 min, should be selected. Conversely, optimizing the content of bioactive components would involve choosing the longest US treatment time and medium to high ultrasonic power during drying. These results provide actionable insights for the industry to tailor drying parameters based on the desired product attributes. Full article

This study evaluates the effects of gliding arc discharge low-temperature plasma (GAD-LTP) pretreatment on the drying performance and quality attributes of blueberries. Fresh blueberries were pretreated under varying conditions—treatment durations of 6 s, 12 s, and 18 s and power levels of 300 W, 600 W, and 900 W—prior to convective hot air drying at 65 °C. Results demonstrate that plasma pretreatment significantly reduced drying time, with an 18 s treatment at 900 W reducing drying time by 31.25%. Moisture diffusion coefficients increased with both treatment duration and power. Under optimal conditions, total phenolic content improved by up to 33.47%, while anthocyanin retention initially declined then recovered, reaching a 7.9% increase over the control. However, plasma-treated samples exhibited darker color due to surface etching and oxidation. Rehydration capacity improved, with a maximum enhancement of 27.94%. Texture analysis indicated increased hardness and decreased adhesiveness and chewiness in treated samples. Overall, GAD-LTP pretreatment enhances drying efficiency and preserves bioactive compounds in dried blueberries, offering a scalable approach for industrial application. Full article

This study aims to develop an efficient recovery solution for waste transformer insulating oil, addressing the challenge of incomplete separation of residual oil in existing recovery technologies. A multi-module integrated system is constructed, comprising a waste oil extraction module, a residual oil vaporization module, an exhaust gas treatment module, and an online monitoring module. By combining steps such as oil extraction, residual oil absorption, hot air circulation heating, and negative-pressure low-frequency induction heating, the complete recovery of waste oil is achieved. The recovery process incorporates oil–gas saturation monitoring and an oil–gas precipitation assessment algorithm based on neural networks to enable intelligent control, ensuring thorough recovery of residual oil from transformers. The proposed system and methods demonstrate excellent recovery efficiency and environmental protection effects during the pre-treatment of waste transformer oil. Experiments conducted on 50 discarded transformers showed an average recovery efficiency exceeding 99%, with 49 transformers exhibiting no damage to core components after the recovery process. From a theoretical perspective, this research introduces monitoring and control methods for transformer insulating oil recovery, providing significant support for the green processing and reutilization of discarded transformer insulating oil. From an application value perspective, the recovery process helps reduce environmental pollution and facilitates the disassembly of transformers. This enables better analysis of transformer operating characteristics, thereby enhancing the reliability and safety of power systems. Full article

Fruit and vegetable industrialisation is a major contributor to food waste; thus, its integral transformation into functional powders has gained attention. Pretreatments can be incorporated into valorisation processes to generate structural or biochemical changes that improve powders’ characteristics. This study deepens into the impact of biological (fermentation, FERM) and thermophysical (autoclaving, AUTO; microwaves, MW; ultrasound, US; and pasteurisation, PAST) pretreatments, combined with dehydration (hot air-drying, HAD; or freeze-drying, FD) on the characteristics of powdered products obtained from broccoli stems. The impact of pretreatments on physicochemical (moisture, water activity, total soluble solids) and antioxidant properties (phenols, flavonoids, antioxidant capacity by ABTS and DPPH) on residue and powdered products was studied, together with their impact on plant tissue structure (Cryo-SEM) and the powders’ phenolic profile (HPLC). Probiotic viability was also determined on the fermented samples. The pretreatments applied, particularly the ultrasound, improved the antioxidant properties of the broccoli stems compared to the unpretreated samples, in line with microscopic observations. Dehydration did also improve the antioxidant attributes of the broccoli wastes, especially drying at 60 °C. However, pretreatments combined with dehydration did not generally lead to an improvement in the antioxidant properties of the powders. Probiotic properties were preserved in the freeze-dried products (>10⁷ CFU/g). In conclusion, pretreatments may be applied to enhance the antioxidant attributes of broccoli wastes, but not necessarily that of dried powdered products. Full article

Gastrodiae Rhizoma (GE), a popular food in China, is stored and consumed after steaming, which can lead to the degradation of active substances and a decrease in its quality. Therefore, this study explored the potential application of ultra-high-pressure (UHP)-assisted hot air drying in improving the quality of GE. The results indicated that UHP pre-treatment could preserve the original cross-sectional color of GE and increase the degrees of freedom of water in GE samples. Compared with traditional steaming pre-treatment (18 h), UHP pre-treatment at 500 MPa significantly shorted the time (10 h) required for the GE samples to reach drying equilibrium. Meanwhile, the UHP-assisted hot air drying method (60 °C) could reduce the activity of β-D-glucosidase and avoid the degradation of active substances. Finally, UHP pre-treatment improved the neuroprotective activity in vivo. Overall, UHP-assisted hot air drying could improve the quality of GE samples. This study provides a simple method for improving the quality of GE samples and offers a reference for subsequent research on the influence of UHP on GE. Full article

The grinding process is one of the key factors affecting the quality of glutinous rice flour (GRF). As an emerging grinding method, semidry grinding aims to solve the problems of the high yield of wastewater in traditional wet grinding and the high content of damaged starch in dry grinding, in which the water content has a great influence on the quality of GRF. However, semidry grinding has not yet been formally put into production due to limitations such as the long time required to adjust the water content of rice grains. Therefore, this work was carried out to shorten the soaking time of glutinous rice (GR) by hot air pretreatment, and to conduct a systematic and in-depth study of the effect of water content on the quality of GRF, including water distribution, water hydration properties, thermal properties, rheological properties, and microstructure. The results showed that the GRF with higher water content had lower water solubility and higher enthalpy of pasting, which were due to the low content of damaged starch and the high degree of crystallization. The particle size of the GRF became smaller as the interaction between water and starch was enhanced and the GR was softened. In addition, the viscosity and elasticity of the GRF were also improved with an increase in water content. This work provides theoretical guidance for the improvement of semidry grinding to a certain extent. Full article