The drying kinetics, microstructural alteration, and rehydration properties of raspberry samples were studied experimentally in this work. Five different drying programs with the application of microwaves (MW) and ultrasound (US) were used, including convective drying (CV) as a reference test. The drying experiments were performed using a hybrid chamber dryer equipped with airborne ultrasound and microwave generators. The modified Page model was successfully used to describe the drying kinetics of raspberry fruits. Next, microstructural properties (porosity and total pore volume) of the dried samples were determined from the postprocessing of the images which were acquired using a lab-scale X-ray microtomograph. The results show a significantly shorter drying time by 54-64% for CVUS, 69% for CVMW, and 79% for CVMWUS; and a lower energy consumption resulting in energy saving of 14-23% for CVUS, 54% for CVMW, and 59% for CVMWUS as compared to CV. It is also shown that the average drying rate of raspberry samples increases by maximum fourfold with the application of both ultrasound and microwave radiations in CV. In addition, a higher porosity, total pore volume, and a better rehydration property were found for the raspberry samples dried with US than with MW assistance.
In this article, the effect of four drying techniques namely hot air drying (AD), infrared drying (IRD), hot air-assisted radio frequency drying (RFD), and microwave-assisted hot air drying (MWD) on quality attributes of dried peach (Prunus persica) leather (PL) was investigated. Drying tests were conducted at 70°C, air velocity of 1.0 m/s and at fixed power level of 4 W/g for RFD, IRD, and MWD. Moisture distribution, texture, rehydration ratio, color, and microstructure of PL were investigated. The results showed that the samples dried by MWD had the shortest drying time (180 min) followed by IRD (210 min), RFD (210 min) and AD (300 min). Study on microstructure and flavor analysis reveals that IRD gave the best results. Sensory tests using electronic tongue and electronic nose that evaluate the odor and taste profiles of dried PL indicates that IRD produced the best quality among the four drying techniques.
Effects of vacuum pressure duration (t-VPD of 5, 10, 15, and 20 min), ambient pressure duration (t-APD of 3, 5, 7, and 9 min), drying temperature (60, 65, 70, and 75°C), and slice thickness (3, 5, 7, and 9 mm) on drying kinetics, rehydration ratio (RR), water holding capacity (WHC), and microstructure of Chinese ginger were investigated using a pulsed vacuum dryer. Various parameters affecting drying rate significantly of ginger slices except t-APD, and the shortest drying time of 300 min was obtained when the t-VPD, drying temperature, and slice thickness were 10 min, 70°C, and 3 mm, respectively. Weibull model fitted the experimental results better (R 2 > 0.99) than first-order model. RR was increased with increasing of t-VPD while it was decreased with increasing of temperature, and a decreased trend of WHC was observed with increasing temperature or t-VPD. Microstructure observation indicated that increased t-VPD resulted in larger tunnel structure, and high temperature caused the formation of rigid structure, which well explained the changes of RR and WHC of dried ginger. The findings in current work contribute to good understanding of the pulsed vacuum drying behavior and quality of ginger.
In current work, the influences of high-humidity hot air impingement blanching (HHAIB) time (60, 90, 120, and 150 s), drying temperature (60, 65, 70, and 75 °C), and air velocity (6, 9, and 12 m/s) on drying characteristics and quality attributes of broccoli florets were explored. Extreme learning machine (ELM) was employed to describe the drying behavior of broccoli florets. Results showed that proper HHAIB pretreatment can extensively increase drying rate compared to the control group (unblanched samples). The entire drying process of broccoli florets occurred in the falling period. Besides, proper HHAIB pretreatment can enhance vitamin C preservation, the color quality, and the rehydration capacity of dried broccoli florets. Based on error analysis results, the prediction accuracy of the optimal ELM model with 4-50-1 topology is found to be satisfied for the moisture ratio prediction of broccoli florets during air impingement drying process, with the R 2 , , and MSE reached to 0.9993, 8.04e −5 , and 2.01e −4 , respectively.
In the spray drying process, variation of outlet temperatures significantly influence the microencapsulation efficiency of fish oil and chia oil. Oil sprayed at 55 °C showed maximum encapsulation efficiency and minimum peroxide value. FTIR spectra of the capsule proved the presence of PUFA in all encapsulated samples. The spectra of microcapsules and unencapsulated samples followed the same trend, implying no interaction between the wall and core. Size of particles were found to be 5.04 and 3.89 µm for chia oil and fish oil powders, respectively; the surface showed blowholes indicating a shell structure with smooth surface. Fatty acid profile of samples indicated a considerable retention of essential fatty acids in both oil powder samples. Maximum release in gastrointestinal conditions was observed, indicating that the capsules were more stable under acidic conditions and that maximum oil would be available for absorption in the intestine.
Radio frequency (RF) drying is an effective and practical dielectric drying method for food and agricultural products due to rapid and volumetric heating, deep penetration and moisture self-balance effects. However, non-uniform heating and sometimes runaway heating are still major problems with implementation of RF drying. RF-related combination drying takes advantages of both conventional drying methods and RF heating, leading to improved drying uniformity, better product quality and higher energy efficiency. This paper provides a brief introduction on the basic principle of RF drying, analyzes the RF heating and drying characteristics and examines recent literature on RF drying applications and possible methods for improving RF heating and drying uniformity. Recommendations for future research have been proposed to achieve practical and effective RF drying requirements and bridge the gap between academia and industry.
In this study, dehydration kinetics of ultrasound and microwave combined vacuum frying (UMVF) of apple slices was investigated and the most suited model predicting the drying kinetics was determined. The variation in dielectric properties (DPs) during frying of apple slices was determined to understand the heating behavior in microwave electric fields. In addition, oil uptake, texture properties and color parameters were also measured and analyzed. Two microwave (MW) power levels (800 and 1000 W) were used at a constant ultrasound power and frequency of 600 W and 28 kHz, respectively. The experimental frying data of apple slices were used to fit ten different mathematical models and non-linear regression analysis was used to determine model parameters. The goodness of fit was determined using the coefficient of determination (R 2 ), reduced chi-square (Σ 2 ), root mean square error (RMSE). The Logarithmic model was found to be the most suitable for describing the frying process. By increasing MW power, the effective moisture diffusivity values increased from 1.7791 to 2.2761 × 10 −9 m 2 /s. The results have shown that the dielectric constant (e′) and loss factor (e″) of the apple slices decreased significantly with increasing frying time and the combination of ultrasound in both MW power levels. The combination of ultrasound with microwave significantly increased the penetration depth compared to when microwave vacuum frying (MVF) was used. The oil uptake of fried apple slices was reduced in UMVF compared to MVF. At the same time textural crispiness and color perimeters significantly improve in UMVF process. UMVF had greater advantages on moisture evaporation rate and uniform heating compared to MVF and it can be confidently used to produce crispy, desirable texture, healthier, and visually appealing fried foods in short time.
A continuous challenge for spray drying operations is the optimal control of product quality despite the complex process removal of water and particle formation. In general, high product functionality (e.g. in terms of reconstitution behavior, high enzyme activity or appropriate living probiotic bacteria) is key to the success of spray-dried powders. In this article, we review scientific studies that employ single droplet drying approaches to unravel underlying phenomena of spray drying process. Moreover, we identify scientific challenges to advance single droplet drying studies and thus contribute to development of mechanism-based guidelines for spray drying of functional food powders.
Evaporative drying of lignite is an energy intensive process. In this study, the heat pump is integrated with a lignite drying system to decrease the energy consumption rate of lignite drying. The performance of heat pump drying is energetically and exergetically evaluated with developed models. Results show that the power consumption rates to dehydrate 1 kg of water from raw lignite in the heat pump drying system without and with lignite preheater are 660.82 and 585.62 kJ (kg H 2 O) − 1 , respectively. Exergetic analysis indicates that most exergy is destructed in the condenser and the evaporator in the heat pump drying. The case of lignite-to-electricity process (i.e., a lignite-fired power plant integrated with heat pump drying) is studied to examine additional benefits of heat pump drying to the downstream industrial processes that consume dried lignite. Thermodynamic and economic models are developed. Net efficiency of the lignite-to-electricity process can be increased by 1.4 and 1.57 percentage points for heat pump drying without and with lignite preheater, respectively. Preliminary economic analysis shows that the integration of heat pump drying without and with lignite preheater can earn additional 1.42 and 1.73 million USD, respectively. The influences of drying system and heat pump parameters are also analyzed.
Non-destructive analysis of water dynamics during drying is of importance for quality control of food products. In this study, different water dynamics and migration in Fuji apple slices dried at various hot-air oven temperatures, i.e. 50, 60, 70, and 80 °C and air velocity at 0.2 m/s were monitored using low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI). Multi-exponential fitting of the transverse relaxation T 2 parameter demonstrated four distinct water peaks in all samples corresponding to strongly bound, lightly bound, entrapped/immobilized, and free water as follows: T 21 in the range of 0.01-1 ms, T 22 in the range of 1-10 ms, T 23 in the range of 10-100 ms, and T 24 in the range of 100-1000 ms, respectively. The water content was measured and analyzed by the traditional technique using the oven drying method. The overall results were highly significant, depicting that the transverse relaxation times T 24 , signal per mass of the free water A 24 , and water content significantly decreased (p< 0.05), while the color (L*, a*, b*) and shear force (SF) curves increased with extended drying. Furthermore, good correlations were observed between the LF-NMR parameters and color, water content, and SF in differently processed samples during the dehydration process. Scanning electron microscopy (SEM) and MRI provided the structural changes and spatial water distributions during the drying process. LF-NMR exhibited great potential in evaluating the various water dynamics and quality of Fuji cultivar apples during the drying process. Abbreviations: AA: ascorbic acid; ANOVA: analysis of variance; CPMG: Carr-Purcell-Meiboom-Gill; DW: distilled water; F: Fuji; LF-NMR: low-field nuclear magnetic resonance; MRI: magnetic resonance imaging; SE: spin-echo; SEM: scanning electron microscopy; SF: shear force; SIRT: simultaneous iterative reconstruction technique; TE: echo time; TR: repetition time.
Drying is one of the most vital preservation techniques used in the food industry. It demands different levels of energy to produce commercially high-quality-dried food products. Novel drying technologies minimize deterioration of the food ingredients and produce novel products for consumers. In recent years, there have been many developments in the technology connected with the industrial drying of foods. Recent research has shown that novel food drying technologies could be utilized to improve the efficiency of drying by lowering the energy consumption and also to enhance the product quality. This article reviews selected energy- saving techniques in drying and discusses some novel combined drying technologies. These include solar-assisted, infrared-assisted, microwave-assisted and similar hybrid drying methods for food drying. Recommendations are also made for future research and development.
Beech wood has a high frequency of defects such as red heartwood, reaction wood (tension wood). For the experimental measurements four logs without visible defects like red heartwood, which can noticeably affects the measurements' results were qualified. The drying medium temperature in the first phase of the process before the moisture content of the specimens fell below the FSP was maintained at 45 °C. Then, the temperature was gradually increased to the maximum value 65 °C. The results showed that different initial wood moisture content does not affect to final value of tension and normal wood. The colorimetric parameter L* was much higher for tension wood. After steaming, there were greater differences in the colorimetric parameters, respectively, a* and b*. After drying the difference of all colorimetric parameters between tension and normal wood was significantly less. The color changes were only noticed in the surface layers of specimens. Differences were small, and thus, the impact of the tension wood on the color changes was not confirmed. However, since the lightness of tension wood plays a key role for its visual detection, it may be adequate to only measure the lightness parameter (L*).
Modern physical field technologies mainly include microwave, radio frequency, infrared radiation, ultrasound, pulsed electric field, and so on. Nowadays, the application of physical field technology on conventional drying is one of the recent strategies to solve some problems in traditional drying. In this article, physical field-based drying techniques refer to hybrid drying methods consisting of the conventional heating combined with different physical field technologies, in which physical field technologies provide various heat sources differ from conventional ones. A review is presented of recent five-year literature in the development of selected physical field-based drying technologies (microwave, radio frequency, infrared radiation, and ultrasound) for fruits and vegetables. As shown by examples from the literature, these physical field-based drying techniques provide faster drying kinetics and better thermal efficiency and obtain dried products of improved quality (e.g. color, aroma, texture, and nutrition retention) relative to conventional hot air drying. The combination of these techniques and conventional hot air drying showed enhanced cost-effectiveness as well. Furthermore, recommendations are made for further research and development needs and opportunities in this area.
Pretreatments of blanching (BL); osmotic dehydration at 35°Brix of sucrose (OD); ultrasound in distilled water (UD), and ultrasound-assisted osmotic dehydration (UO) were carried out for microwave-vacuum drying (MVD) orange- and purple-flesh sweet potato slices, and effects on their properties were investigated in this study. UO had improvements effects on water loss, solid gain, and relaxation time of the samples compared to other pretreatments. Low-field nuclear magnetic resonance results offered a view of water state concerning the effects of different pretreatments on sweet potato. UD treatment following by BL showed a long relaxation time corresponding to the weaker degree of bound hydrogen proton or the greater freedom degree of hydrogen comparing to other pretreated samples. Differential scanning calorimetry parameters appeared to be sensitive to pretreatments by increased Tg value compared to blanched sample. The value of Tg shows that it does not depend only of the water content but also on the experimental conditions (pretreatments). The dried sweet potato exhibited amorphous structures as evidenced by the X-ray diffractograms due to the BL treatment and MVD. Concentration of total phenolics and anthocyanins were high in purple sweet potatoes, whereas content of vitamin C and total carotenoid were high in orange ones. Application of UO is suitable for retention of bioactive compound and stability of MVD sweet potato slices.
Conductive hydro-drying also known as Refractance Window drying is a relatively new drying technology, which uses hot water to carry thermal energy to materials to be dehydrated. It has a high retention of heat sensitive quality parameters (vitamins, antioxidants, and color) with better energy efficiency than freeze-drying as well as many other conventional drying methods. A new ultrasound and infrared assisted conductive hydro-dryer (UIACHD) was developed to increase drying rate while reducing required hot water temperature and increasing the drying material thickness. The goal of this study was to evaluate the performance of the new dryer and to compare the performance of a pilot scale continuous UIACHD with a freeze-dryer and a cabinet dryer in drying apple slices. The physiochemical characteristics of the dried apple slices including flavonoid content, total phenolic compounds, antioxidant activity, vitamin C content and color were measured. In addition, the energy consumption and energy efficiency of the dying methods were evaluated. Results showed that combining ultrasound and infrared with conductive hydro-drying can result in higher drying rates and lower product moisture content. Quality of UIACHD dried apple slices was close to the freeze-dried products and it was significantly better than the cabinet dried products. Moreover, the energy efficiency of UIACHD was considerably better than the cabinet dryer and the freeze-dryer. The results of this study showed that combining ultrasound and infrared with conductive hydro-drying can lead to an energy-efficient process with good quality retention ability.
Grape is one of the most popular fruits and various types of grape have been cultivated by more than 100 countries around the World. The wine and juice industry produces large quantities of by-product, called grape pomace (GP) as an industrial waste and it consists of skins, seeds, and stems. Various processes such as separation, pressing, drying, and milling are applied to benefit from its health effects. In this study, the seeded black GP Kalecik karası (Vitis vinifera) was dried in an assisted closed cycle heat pump dryer (HPD) designed for high-moisture products to investigate the drying behaviors of GP. The effects of drying air temperature on bioactive properties and the drying characteristics of GP, and performance of system have discussed. Experiments were carried out at two different temperatures (45 and 50°C) and air velocity of 1.0 m/s. It was seen that increasing temperature decreased the drying time, coefficient of performance of whole system (COP ws ), and specific energy consumption (SEC). The average values of COP ws for temperatures 45°C and 50°C were calculated as 3.28 and 3.10, respectively. The drying efficiencies (DE) at drying air temperature of 45°C and 50°C ranged from 2 to 12% and from 2 to 15%, respectively. Additionally, result of analysis has indicated that using a HPD at lower temperatures increases performance of system despite of higher energy input. Bioactive properties of dried samples at drying air temperature of 45°C are better than 50°C. The results show that drying the GP at low temperature is more suitable for product quality. For this reason, heat pump may be preferred. It shows that this drying system with higher capacities in the future can be recommended as an alternative technique in terms of energy usage, drying time, and performance of system.
Using ultrasound (US) at microwave-assisted vacuum Frying (MVF) program was investigated to acquire better process efficacy and bodily high-quality attributes of fried edamame. Different power degrees of US (0, 150, 300, 600 W) and temperature (80, 90, and 100 °C) were utilized in a constant microwave power and frequency of 1000 W and 28 kHz during ultrasound and microwave-assisted vacuum frying (USMVF) process. Ten different mathematical models were employed to describe dehydration kinetics of the fried edamame, and nonlinear regression analysis was used to determine model parameters. Concerning fitting performance, the most suitable model was the two-term model. Drying kinetics, effective moisture diffusivity (D e ), activation energy (E a ), and physical properties of fried samples were evaluated in this newly designed USMVF equipment using different ultrasound power to the studied temperature range. By increasing the US power level, the calculated D e increased from 1.947 × 10 −9 to 4.742 × 10 −9 m 2 /s. The results have revealed that the E a of this fried edamame decreased significantly with increasing the US power level. The USMVF process at every frying temperature increased the drying kinetics and D e when compared to the non-USMVF process. The USMVF samples always gave lower oil content and water activity in contrast to the non-USMVF samples. The color and texture properties of fried edamame were significantly improved and higher the US power level in the USMVF produced a better progress. Vitamin C and chlorophyll retention of fried edamame was highest in US600MVF process.
This study investigated drying kinetics and changes in water in rosebuds during hot air drying at 40, 50, 60, and 70 °C, using NMR and MRI technology to evaluate transverse relaxation times (T 2 ), water status and distribution. Drying rate increased with temperature, with the Midilli model predicting the drying process of rosebuds more accurately than other mathematical models. Three water fractions with different T 2 values were identified: T 21 (0.1-2 ms), T 22 (5-50 ms), and T 23 (50-600 ms). Water status and distribution in rosebuds differed with a higher moisture content in receptacles than in petals. During drying, the total peak amplitude and T 2 values in rosebuds declined (LF-NMR), with changes in internal water distribution shown by MRI. Moisture content was significantly correlated with LF-NMR parameters, especially A Total /g. Therefore, the Midilli model described the drying of rosebuds, and LF-NMR and MRI technology can monitor changes in water status and distribution during drying.
The aim was to study the effect of sublimation temperature (from -20 °C to -10 °C) and sublimation time (from 18 to 40 h) on the viability of Lactobacillus fermentum K73, the moisture content and the texture features by response surface methodology. The stability of the freeze-dried powders was studied; these powders were stored at 4 °C, 25 °C, and 37 °C for 36 days. Four different matrices were used: culture medium (8% total solids), the mixture of this solution with maltodextrin: whey (0.6: 0.4), with maltodextrin or whey (40% total solids). Results showed that the sublimation conditions to increase cell viability (>8.755 log CFU/g) and to decrease moisture content (<4.087% [wet basis]) in the mixtures were -10 °C and 18 h. The image analysis successfully correlated sublimation temperature and time with the structural characteristics of the powders, cell viability, and moisture content. The shelf life study showed that the specific rate of cell viability loss was lower when the freeze-dried powders were stored at 4 °C, being the denatured whey solution the best cryoprotectant matrix during the freeze-drying process and shelf life.