Effects of hot air, vacuum infrared, and vacuum microwave dryers on the drying kinetics and quality characteristics of orange slices

Effects of different drying methods on the drying kinetics and quality characteristics of Orah (Citrus reticulata) slices

This study evaluated the effects of microwave vacuum drying (MVD), microwave drying (MD), heat pump drying (HPD), hot air drying (HAD), and freeze drying (FD) on the drying kinetics, and changes of physicochemical properties and bioactive compound of Orah slices. In the analysis of the seven models examined, the Page model was found to be the most accurate in describing the changes in moisture content during the drying process. MD was significantly faster than HAD and HPD, reducing drying time by 95.12 and 94.17%, respectively, and increasing the effective moisture diffusion rate by 94.40%. Microscopic analysis showed MVD samples had large, uniform pores, which improved moisture diffusion. FD and MVD preserved bioactive nutrients and demonstrated superior antioxidant activity over other methods. MVD produced products with balanced texture, minimal color change, and the shortest drying time of 38 min. MVD can be a promising dehydration technique for producing high-quality Orah products.

Assessment of thermophysical properties of the temperature profile created on peach by microwave energy

Microwave energy is based on creating heat in the structure by creating vibrations in the moisture in the product used. In drying processes, drying kinetics, energy consumption, quality, and so on features are evaluated based on the temperature equivalent of the heat created by the heat source in the product. For this reason, the temperature value formed in the product in microwave drying processes is important. In this study, the effects of microwave drying powers (180, 540, 720, and 900 W) on the surface temperature profile, drying kinetics, thermophysical properties, and color values of peach slices were investigated. For drying processes performed at 180, 540, 720, and 900 W microwave powers, the surface temperatures of peach slices were 34.5-83.40, 49.60-89.60, 55.90-94.06, and 68.20-145.20°C, respectively. Effective diffusion values varied between 1.01 × 10-7 and 2.12 × 10-7, and the activation energy value was measured as 20.73 kJ/mol. Specific heat values varied between 871.62 and 838.21 J/kg K, density values varied between 839.41 and 697.93 kg/m3, thermal diffusivity values varied between 5.69 × 10-7 and 2.344 × 10-7 m2/s and thermal conductance values ranged between 0.44 and 0.08 W/m K. As compared to the fresh fruits, the best color values of dried material were achieved at 720 W microwave power. It is recommended to determine the microwave drying power value well and to determine the drying kinetic properties of each agricultural product specifically for the product.

Hot air-assisted radio frequency drying of orange slices: Drying behavior and product quality

This research aimed to assess the hot air-assisted radio frequency drying (HA-RFD) of orange slices to evaluate the possibility of producing high-quality dried orange slices and overcome the problem of the long drying time and the high energy consumption. The effect of electrode distance (60, 70, and 80 mm) and number of slices (1-3 slices; 4 mm thickness per slice) on the HA-RFD of orange slices was evaluated. Orange slices in three layers with a total thickness of 12 mm and an electrode gap of 70 mm were picked to dry the orange slices in the shortest time. The quality of orange slices dried with HA-RFD was compared with those of HA-dried (HAD) and freeze-dried (FD) samples. HA-RFD allowed a 67% decrease in the time of drying of the orange slices (from 1170 to 390 min) when compared to HAD. Total phenolic content (TPC), total flavonoid content (TFC), antioxidant activity, and color values were affected by the drying technique. HA-RFD showed higher TPC, TFC, and antioxidant activity than HAD. The FD samples showed the highest TPC (928 mg GAE/100 g dw), TFC (200 mg rutin/100 g dw), and antioxidant activity (67.58%). Moreover, the samples dried with HA-RFD resulted in the least color change in comparison to HAD and FD samples. Regarding vitamin C, FD samples were the best, followed by HA-RFD and HAD, respectively. Considering the final product quality, and the characteristics of drying techniques, especially drying time and drying rate, HA-RFD proved to be an alternative technique to the HAD for producing dried orange slices. PRACTICAL APPLICATION: HA-RFD was applied for the first time as an alternative technology to dry orange slices. The quality of orange samples dried by HA-RFD was compared with samples that dried by HAD and FD. The results indicated that the HA-RFD technique is a good method to dry orange slices by considering the drying characteristics and the final product quality.

Quality Evaluation and Heat and Mass Transfer Mechanism of Microwave Vacuum Drying of Astragalus Roots

In this research, the objective was to optimize the drying process of Astragalus by investigating the effects of microwave vacuum drying parameters, including temperature (30, 35, 40, 45, and 50 °C) and slice thickness (2, 3, 4, 5, and 6 mm). In addition, utilizing COMSOL 6.0 finite element analysis software, we delved into the distribution of heat and moisture during the drying process. The results revealed that drying temperature played a significantly greater role than slice thickness in determining the drying dynamics. The thermal and mass transfer mechanism indicated that the whole drying process conforms to the microwave radiation mechanism and the basic principle of electromagnetic heating. In the case of low temperatures and thinner slice sizes, the more polysaccharide content was retained; The total phenol content peaked when the slice thickness was 5 mm; The increase of slice thickness was not conducive to the retention of total flavonoids content. The potent antioxidant capacity was detected at a temperature of 40 °C, with slice thickness having a negligible effect on this capacity; Low temperatures were beneficial for the preservation of active ingredients. Compared with the scanning electron microscope, the structure appeared more uniform at a temperature of 50 °C. Based on the analysis of the kinetic characteristics of microwave vacuum drying of Astragalus and the quality achieved under various drying conditions, the results of the study can provide valuable guidance for controlling the quality of microwave vacuum drying of Astragalus under different drying requirements.

Pulsed vacuum drying of fruits, vegetables, and herbs: Principles, applications and future trends

Pulsed vacuum drying (PVD) is a novel vacuum drying method that has demonstrated significant potential in improving energy efficiency and product quality in the drying of foods and agricultural products. The current work provides a comprehensive analysis of the latest advancements in PVD technology, including its historical development, fundamental principles, and mechanistic aspects. The impact of periodic pulsed pressure changes between vacuum and atmospheric pressure on heat and moisture transfer, as well as structural changes in foods at micro- and macro-scales, is thoroughly discussed. The article also highlights the influential drying parameters, the integration of novel auxiliary heaters, and the applications of PVD across various fruits, vegetables, and herbs. Furthermore, the review examines the current status and needs for mathematical modeling of PVD processes, identifying key challenges, research opportunities, and future trends for industrial application. The findings suggest that PVD not only enhances drying efficiency and reduces energy consumption but also preserves the nutritional value, color, and texture of dried products better than traditional methods. Future research should focus on optimizing process parameters and integrating advanced control systems to further improve the scalability and applicability of PVD technology in the food industry.

Prevention of the Quality Degradation of Antarctic Krill (Euphausia superba) Meal through Two-Stage Drying

To achieve a krill meal of high quality, a two-stage drying involving hot-air drying and vacuum drying was investigated. Five experimental groups were established according to the different drying conditions in the second stage, including 95 °C and 101 kPa, 95 °C and 60 kPa, 75 °C and 101 kPa, 75 °C and 60 kPa, and 75 °C and 20 kPa. The results showed that reducing the drying temperature and vacuum pressure in the second stage had a significant impact on the drying characteristics, sensory quality, and bioactive compounds of krill meal. Among all five groups, the drying condition of 75 °C and 60 kPa maintained a high drying rate while preserving a phospholipid content of 30.01 mg/kg and an astaxanthin content of 37.41 mg/kg. It also effectively reduced the isomerization of astaxanthin and the oxidation of unsaturated fatty acids. These results suggested that the two-stage drying method may contribute to the production of high-quality krill meal.

Dried Beetroots: Optimization of the Osmotic Dehydration Process and Storage Stability

In this study, beetroots were osmotically dehydrated in sugar beet molasses. The input parameters of the drying process were varied: temperature (20 °C, 40 °C, and 60 °C), time (1 h, 3 h, and 5 h), and concentration of sugar beet molasses (40%, 60%, and 80%). Basic quality indicators were determined for the dried beetroot samples: dry matter content, water loss, solid gain, mineral and betaine content, and phenols and flavonoids, as well as antioxidant potential. After optimizing the results, favorable drying parameters were selected: temperature 60 °C, molasses concentration 70%, and processing time 5 h. According to the optimal drying conditions, the beetroots were dried and stored at 4 °C for 28 days. Half of the dried samples were coated with an edible biopolymer coating based on Camelina sativa oilcake, while the other half of the samples remained uncoated. The sustainability study aimed to confirm the effects of the biopolymer coating on the quality and sustainability of the osmotically dried beetroots.

Kinetic Modeling of Convective and Microwave Drying of Potato Peels and Their Effects on Antioxidant Content and Capacity

This study deals with drying properties and focuses on the drying kinetics of potato peels (PP) by two processes, namely convection drying (CD) at various temperatures (40, 60, 80, 100, and 120 °C) and microwave drying (MD) at different powers (200, 400, 600, and 800 W). In addition, the effectiveness of the adopted processes was evaluated in terms of antioxidant contents and antioxidant capacity. A total of 22 mathematical models were undertaken to predict the drying kinetics, and the best model was selected based on the highest R2 values and the lowest χ2 and RMSE values. The Sledz model was the more appropriate for both methods with values of 0.9995 ≤ R2 ≤ 0.9999, χ2 = 0.0000, and 0.0054 ≤ RMSE ≤ 0.0030 for CD, and the results of MD were 0.9829 ≤ R2 ≤ 0.9997, 0.0000 ≤ χ2 ≤ 0.0010, and 0.0304 ≤ RMSE ≤ 0.0053. The best drying rates (DR) of PP were assigned to a temperature of 120 °C and a power of 600 W with values of 0.05 and 0.20 kg water/kg dw min, respectively. A potential explanation is that as PP’s moisture content decreased during the drying process, there was a drop in absorption, which led to a reduction in the DR. The energy consumption of both processes was assessed, and it rose with increasing temperature or power. The microwave process reduced the drying time, consumed lower energy, and presented a higher drying efficiency at a moderate power level compared to the convection process. Furthermore, MD preserved antioxidants better compared to CD and improved the antioxidant capacity. Therefore, the proposed microwave process for drying PP is suggested for its expected use in various fields, including the food processing industries.

Optimization of Convective Tray-Drying Process Parameters for Green Banana Slices Using Response Surface Methodology and Its Characterization

Green banana (Musa spp.) is a significant source of starch (resistant starch ∼50%), phenolics and flavonoid compounds, and minerals (K, Mg, Zn, and Fe). The utilization of green bananas in their fresh form is limited, whereas the drying of bananas provides the opportunity to use them for various purposes. Drying temperature and slice thickness are important to be optimized for drying of bananas as they affect the quality parameters. The present study was conducted using response surface methodology to optimize tray-drying temperatures (50–80°C) and slice thicknesses (2–8 mm) on the basis of phytochemical and physical parameters of dried green banana slices. The cubic model was found to be the best fit for most of the responses (R2 = 0.95–1), and the quadratic model was fit for water activity ( ${\mathrm{a}}_{\mathrm{w}}$ ) (R2 = 0.92). The optimized drying conditions were found as drying temperature of 50°C and slice thickness of 4.5 mm. Experimental responses exhibited maximum L ${}^{\ast }$ (84.06), C ${}^{\ast }$ (13.73), and ho(83.53) and minimum losses of total phenolic content (89.22 mg GAE/100 g) and total flavonoid content (3.10 mg QE/100 g) along with lower ${\mathrm{a}}_{\mathrm{w}}$ (0.25). The optimized green banana flour was rich in carbohydrates (77.25 ± 0.06%) and low in fat (1.79 ± 0.11%). The flour obtained had good flowability with a mean particle size of 60.75 ± 1.99 µm. Flour’s gelatinization and decomposition temperatures were 102.7 and 292°C, respectively. In addition, flour’s water absorption, oil absorption, and solubility were 5.19 ± 0.01, 1.58 ± 0.01, and 0.14 ± 0.02 g/g, respectively. Green bananas dried at optimized conditions resulted in a better product with less phytochemical loss than dried with other methods.

Pulsed electric field-assisted drying: A review of its underlying mechanisms, applications, and role in fresh produce plant-based food preservation

Drying is a key processing step for plant-based foods. The quality of dried products, including the physical, nutritional, microbiological, and sensory attributes, is influenced by the drying method used. Conventional drying technologies have low efficiency and can negatively affect product quality. Recently, pulsed electric field (PEF)-assisted techniques are being explored as a novel pretreatment for drying. This review focuses on the application of PEF as pretreatment for drying plant-based products, the preservation effects of this pretreatment, and its underlying mechanisms. A literature search revealed that PEF-assisted drying is beneficial for maintaining the physicochemical properties of the dried products and preserving their color and constituent chemical compounds. PEF-assisted drying promotes rehydration and improves the kinetics of drying. Unlike conventional technologies, PEF-assisted drying enables selective cell disintegration while maintaining product quality. Before the drying process, PEF pretreatment inactivates microbes and enzymes and controls respiratory activity, which may further contribute to preservation. Despite numerous advantages, the efficiency and applicably of PEF-assisted drying can be improved in the future.

Effect of different drying technologies on the characteristics and quality of lemon slices

This experiment aimed to investigate the effects of four drying methods, namely, hot air drying (HAD), microwave drying (MD), vacuum drying (VD), and microwave vacuum drying (MVD), on the quality of lemon slices. The relevant indicators, including total phenolic content, ascorbic acid content, browning, color, reducing sugar content, volatile component measurements, and principal component analysis of 0 and 30 days storage, were compared after exposure to the four drying methods. The shortest time of 64 min was used to treat the lemon slices via MVD at 1 KW. These samples displayed the least damage after drying and the highest rehydration ratio of 4.12. The contents of VC, reducing sugars, and total phenols of MVD samples were significantly higher than those in the HAD, VD, and MD groups, retaining 105.94 mg/100 g, 21.35 g/100 g, and 77.81 mg GAE/g, respectively, while their color difference values were also the smallest, with a browning degree of 3.55, significantly lower than those in the other treatment groups (p < 0.05), and the degree of browning of the samples in the HAD treatment group was the most serious; in terms of volatile flavor substances, the lemon slice samples in the MVD and HAD treatment groups were more diverse and of better quality. The order of product sensory evaluation was: MVD > VD > HAD > MD. The final scores after comprehensive analysis revealed the order of the four drying methods as MVD, HAD, VD, and MD. Therefore, MVD had a better effect on the sensory perception and nutritional properties of the lemon slices, providing a useful alternative to the conventional drying method. PRACTICAL APPLICATION: Lemon slices during drying are affected by various aspects, leading to changes in its color, aroma substances, and nutrient composition. The results of this work will not only provide a technical reference for the future production of high-quality dried lemon slices, but also have important implications for fresh-cut lemons in processing and storage. It also generates important implications for fresh-cut lemons in processing and storage.

Microwave and convective drying kinetics and thermal properties of orange slices and effect of drying on some phytochemical parameters

We dried the orange slices massed 100 ± 0.10 g from the initial moisture content of 6.97 ± 0.02 kg _water kg_DM ^-1 to the final moisture ones of 0.12 ± 0.01 kg _water kg_DM ^-1 using two different drying methods defined as convective drying at 50, 75, 100, and 125 °C along with microwave drying at eight output power between 90 and 1000 W. In the study, we measured the drying methods' energy consumption and observed that the microwave drying method's energy consumption was very low at high and low powers. Also, we modeled the results using twenty-one different thin-layer drying equations and obtained results closest to experimental data with the modified Henderson and Pabis equation for all powers in microwave drying and all temperatures in convective drying. We calculated both effective moisture diffusivities and activation energy using the drying data. Some thermal properties such as specific heat, thermal conductivity, thermal diffusivity, and thermal effusivity were calculated and recorded to be decreasing in all thermal properties with drying. Also, we measured the color parameters known as L, a, b, C, α°, and ΔE, browning index (BI), whitening index (WI), and vitamin C (ascorbic acid) in the study. We concluded that the most suitable drying method is microwave drying at medium powers of 350 and 500 W by considering both drying and quality parameters.

Effect of Alternative Preservation Steps and Storage on Vitamin C Stability in Fruit and Vegetable Products: Critical Review and Kinetic Modelling Approaches

Vitamin C, a water-soluble compound, is a natural antioxidant in many plant-based products, possessing important nutritional benefits for human health. During fruit and vegetable processing, this bioactive compound is prone to various modes of degradation, with temperature and oxygen being recognised as the main factors responsible for this nutritional loss. Consequently, Vitamin C is frequently used as an index of the overall quality deterioration of such products during processing and post-processing storage and handling. Traditional preservation methods, such as thermal processing, drying and freezing, are often linked to a substantial Vitamin C loss. As an alternative, novel techniques or a combination of various preservation steps ("hurdles") have been extensively investigated in the recent literature aiming at maximising Vitamin C retention throughout the whole product lifecycle, from farm to fork. In such an integrated approach, it is important to separately study the effect of each preservation step and mathematically describe the impact of the prevailing factors on Vitamin C stability, so as to be able to optimise the processing/storage phase. In this context, alternative mathematical approaches have been applied, including more sophisticated ones that incorporate parameter uncertainties, with the ultimate goal of providing more realistic predictions.

A study of the freeze-drying process and quality evaluation of Angelica sinensis

The freeze-drying process of Angelica sinensis (Oliv.) Diels was studied and evaluated. Using a single factor investigation, drying temperature and pressure were determined as the main factors affecting the drying process. The central composite design (CCD) combined with response surface method was employed to optimize the drying process. Optimal conditions were determined to be 52 Pa, 63 °C, and a slice thickness of 5 mm. Subsequently, samples were compared in terms of chemical constituents, microstructure, and in vitro absorption profiles under different drying operations. The freeze-drying process was effective for the preservation of ferulic acid (1.82 mg/g), Z-ligustilide (13.91 mg/g), and other compositions. The porous and loose characteristic structure enabled rapid release of ferulic acid (71%, 60 min) and Z-ligustilide (32%, 60 min). Therefore, the freeze-drying method is a reasonable and efficient drying method for the dehydration of A. sinensis.