Development of phase change material assisted evacuated tube solar dryer: Investigation of thermal profile, drying characteristics, and functional properties of pumpkin slices

Effects of freeze-hot air drying on physicochemical properties and anti-tyrosinase activity of quince peels

Xinjiang quince peels (XQP) are rich in bioactive compounds and have anti-tyrosinase potential. However, due to their short shelf life, effective preservation techniques are needed to retain their nutritional and medicinal properties. While freeze drying (FD) is effective, combining FD with hot air drying (HAD) offers greater efficiency. The study aimed to evaluate the effects of freeze-hot air drying on the physicochemical properties and anti-tyrosinase activity of XQP. The results showed that peels subjected to FD for 18 h followed by HAD for 0.3 h (FD18-HAD0.3) had the highest contents of total phenolics, total flavonoids, chlorogenic acid, rutin, and ascorbic acid, while reducing drying time by 25 % compared to FD alone. FD18-HAD0.3 peels also showed the highest anti-tyrosinase activity, with the smallest IC50 value (7.84 ± 0.03 mg/mL). The study concludes that FD18-HAD0.3 showed potential as the optimal drying process for XQP.

Comparison of different drying technologies for kiwifruit pomace: Changes in physical characteristics, nutritional properties and antioxidant capacities

The objective of this study was to evaluate the impacts of different drying technologies including microwave drying (MD), vacuum microwave drying (VMD), sun drying (SD), vacuum drying (VD), hot air drying (HAD), and vacuum freeze drying (VFD) on the physical characteristics, nutritional properties and antioxidant capacities of kiwifruit pomace in order to realize by-product utilization and improve energy efficiency. Results showed that both MD and VMD significantly reduced drying time by >94.6%, compared to traditional thermal drying which took 14-48 h. MD exhibited the highest content of soluble dietary fiber (9.5%) and the lowest energy consumption. Furthermore, VMD resulted in the highest content of vitamin C (198.78 mg/100 g) and reducing sugar (73.78%), and the antioxidant capacities ranked only second to VFD. Given the financial advantages and product quality, VMD was suggested to be advantageous technology in actual industrial production.

Segmented variable-frequency ultrasound synergistic hot-air drying of Rhubarb: Effect on drying characteristics and quality and thermal analysis

This study employed segmented variable-frequency ultrasound synergistic hot-air drying (SVFU-HAD) for Rhubarb slices, selected two sets of time nodes for frequency conversion (60 min, 120 min, and 90 min, 150 min), and two sequences of frequency conversion (high-frequency to low-frequency, and low-frequency to high-frequency). It aimed to investigate the effects of SVFU-HAD on the drying characteristics, quality, and heat transfer of Rhubarb slices. The findings indicated that segmented variable-frequency ultrasound has advantages in increasing drying rate and improving uniformity of cavitation effects compared to constant-frequency ultrasound. Analysis of physical properties revealed that the rehydration performance of dried products subjected to ultrasonic variable-frequency treatment (90 min, 150 min) according to the drying rate was better (RR > 3.3). The transition mode from high-frequency to low-frequency in variable-frequency ultrasonic treatment contributes to maintaining the overall color of Rhubarb. Analysis of chemical properties unveiled that Rhubarb treated with 40 kHz (0 min)-28 kHz (60 min)-25 kHz (120 min) segmented variable-frequency ultrasound contained overall higher levels of tannins, dianthrones and free anthraquinones content, which exceeded the average values by 3.24%, 26.65%, and 14.42%, respectively. In addition, thermal analysis results based on ANSYS Workbench software demonstrated that the drying uniformity of SVFU-HAD is superior to that of hot-air drying and constant-frequency ultrasound synergistic hot-air drying (CFU-HAD). Overall, the SVFU-HAD method employed in this study presents an innovative approach to ultrasound synergistic hot-air drying research with promising potential for enhancing the efficiency and quality characteristics of Rhubarb slices.

Recent trends and applications of evacuated tube solar collector in food processing and air heating: a review

Solar energy demand is growing for future energy needs in different sectors to replace fossil fuels, which leads to a reduced carbon footprint and global warming. Evacuated tube solar collectors (ETSC) harness solar thermal energy for air heating, water heating, and drying in domestic and industrial sectors. The review paper comprises ETSC technology categorization, influencing factors like fin arrangement, integration of phase change material, tilt angle, solar radiation, and airflow rate on the performance of ETSC-based solar air heaters and dryers. The thermal performance parameters, like the collector efficiency, dryer efficiency, energy and exergy efficiency, thermal profile, zone temperature, relative humidity, heat loss during operations, etc., are reviewed. The developed ETSC-based air heating systems and solar dryers for drying agricultural products are performed effectively. However, research progress on improving the thermal performance integrated with nanofluids and phase change materials was discussed. CO2 mitigation analysis and global standards for ETSC-based air heaters and dryers are compiled. A large scope exists by use of solar air heaters (SAH) for food commodity drying with a suitable drying chamber and improving the designs of ETSC-based solar dryers. The work accomplished by various researchers has been analyzed in this study for prospective research gaps in the context of future design and development.

Investigation of the effects of different processing methods on the selected nutritional properties of pumpkin and determining the appropriate process for pumpkin yogurt

The processing methods, especially cooking, can cause quality losses, particularly in the nutritional value of the fresh product. This study investigated the effects of preprocessing methods on the nutritional properties of pumpkin and the physicochemical and sensory properties of pumpkin yogurt. Two different pumpkin varieties (Cucurbita pepo and Cucurbita maxima) were subjected to three different preprocessing methods (freeze-drying, boiling, and baking). Boiling significantly increased antioxidant activity (p ≤ .05), followed by baking. C. maxima had higher TDF and TPC than C. pepo, but in both pumpkin varieties, TDF did not change with heat treatment (boiling and baking), while TPC decreased. Mineral contents remained the same or decreased with heat treatment, except for Mn and Fe. In particular, the addition of C. maxima significantly affected the color parameters (L*, a*, b*) of yogurt and improved WHC (from 68.9% to 91.6%) and hardness (from 58.0 to 193.5 g; p ≤ .05). The sensory evaluation concluded that heat-treated (boiled and baked) samples were preferred more than freeze-dried raw ones. In conclusion, the results revealed that adding boiled and baked pumpkins, especially the preference for C. maxima instead of C. pepo, improved the quality parameters of yogurt.

Mass transfer analysis and kinetic modeling of ultrasound-assisted osmotic dehydration of kiwifruit slices

Ultrasound treatments (sonication) in combination with osmotic dehydration process accelerate the rate of moisture removal from the fruits or vegetables pieces and decrease the dehydration duration. The purpose of this study was to examine the influence of ultrasound-assisted osmotic dehydration (UAOD) on mass transfer kinetic (soluble solids gain and moisture loss) of kiwifruit slices. The UAOD process was performed using 20, 30, and 40% sucrose solutions in ultrasonic bath (40 kHz, 75 and 150 W) for 10, 20, 30, 40, 50, 60, 70, and 80 min. After treatments, processed kiwifruit slices were dried at 70 °C using hot air oven. UAOD process reveals that mass reduction, soluble solid gain, moisture loss and rehydration capacity affected by treatments time, sucrose solution concentration and sonication power. The results showed that the UAOD treatment increased moisture loss and soluble solids gain. Furthermore, kiwifruit slices treated with higher ultrasound intensity (150 W) showed reduced dehydration duration (higher water loss), improved dehydration rate, and increased effective moisture diffusivity (D_eff). The D_eff determined by Fick's second law was varied from 9.05 × 10^-11 to 29.28 × 10^-11 m²s^-1. The experimental data of dehydration curve of kiwifruit slices were fitted to different thin-layer equations and the Page equation with empirical constants was the best describing the of kiwifruit slices dehydration.