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Image processing techniques are used in several fields and gained popularity in food processing. In this study the drying and shrinkage characteristics of pumpkin slices were determined by using thresholding method. A continuous measurement of the weight change and an imaging of the pumpkin slices to measure the area of the sample before and after drying were performed to define the shrinkage characteristics. The drying times of the pumpkin discs were between 8.5–9 and 55–65 minutes for 2 mm thick samples. Drying in the microwave oven resulted in 85% less time and lower values of water activity were obtained. The shrinkage rate of samples dried by microwave drying method (46–60%) was found to be statistically lower than samples prepared by convection drying method (58–73%) (p < 0.05). Non‐parametric Spearman correlation coefficient technique was used to evaluate the relationship between the moisture content and shrinkage for drying under different conditions. Practical application: With the advancement of image processing technologies, there is significant potential for food safety and preservation. This research will lead to advancements in the fields of food quality and preservation analyses for food manufacturers. Furthermore, this technology can be employed in the food business for quick quality determination for mass production. This research indicates that image processing may be used to evaluate food shrinkage characterization. It is expected that the application of this technology will serve the food sector by optimizing process parameters and energy usage, saving time, and developing sustainable systems, particularly in the large‐scale food industry where mass manufacturing is carried out. [ABSTRACT FROM AUTHOR]

Purple cabbage is one of the world's most widely consumed vegetables with high nutritional values containing the antioxidants and anti‐inflammatory activity of anthocyanins, vitamins, and minerals. But due to rapid postharvest quality decay, novel processing techniques including drying are required. In order to determine the conditions of combined microwave and hot air drying for purple cabbage, factors affecting the drying process including microwave density, hot air temperature, and the dry base water content at conversion point were investigated using the anthocyanin content, DPPH antioxidant capacity, chewiness, △E, rehydration ratio, and average drying rate as responses. The combined drying conditions were optimized considering three independent variables at three different levels by response surface methodology. The results showed that the processing parameters of purple cabbage with combined microwave and hot air drying technology were microwave density at 2.5 W/g, moisture content of conversion point at 4.0 g/g, and hot air temperature at 55°C. Under these conditions, the anthocyanin content, DPPH antioxidant capacity, chewiness, △E, rehydration ratio, average drying rate, and overall score of the dried purple cabbage were 175.87 mg/100 g, 87.59%, 4,521.468 g, 26.5, 4.3, 0.76 g/min, and 0.785, respectively. Therefore, combined microwave and hot air drying technology is an effective, suitable method for drying purple cabbage. [ABSTRACT FROM AUTHOR]

Hot air drying (HAD) at temperatures below the spontaneous evaporation temperature could be combined with microwave (MW) radiation as a thermal energy source in order to reduce the drying time. A photon flux in the microwave range interacts with dipolar molecules (water) through orientation and induction, producing electrical energy storage and thermal energy accumulation and generating an increase in the internal energy of food. The different mechanisms involved in water transport could change when the microwave penetration depth exceeds the sample characteristic dimension of mass transport. The aim of this paper is to determine the effect of MW in the combined HAD-MW drying of raw potato in order to obtain the real driving forces and mechanisms involved in the water transport, with the purpose of optimizing the MW power used. For this purpose, combined drying was carried out on potato samples (0, 4 and 6 W/g). The sample surface temperature was monitored by infrared thermography, and the sample mass was measured continuously through a precision balance. In parallel with continuous drying, another drying treatment was performed at different times (20, 40, 60, 90, 120, 180, 420 min) and conditions (0, 4 and 6 W/g) to analyze the dielectric properties, mass, moisture, volume and water activity. The results show that it is possible to monitor combined drying by infrared thermography, and it can be concluded that the convection heating is mostly transformed into surface water evaporation, with negligible thermal conduction from the surface, and microwave radiation is mostly transformed into an increase in the potato's internal energy. [ABSTRACT FROM AUTHOR]

Broccoli is considered one of the attractive raw materials for dehydrated vegetables owing to its high nutritional value. However, information about how drying methods affect the physicochemical and nutritional properties of broccoli is limited. In this study, broccoli pieces were subjected to freeze drying (FD), hot air drying (HAD), microwave vacuum drying (MVD), vacuum drying (VD), MVD combined with HAD (MVD + HAD), and MVD combined with VD (MVD + VD). Quality attributes of dehydrated broccolis were contrasted in terms of color, texture, volume shrinkage, nutritional components, antioxidant activity, and rehydration capacity. Results demonstrated that FD better preserved the nutrients while HAD displayed the worst effect. The combination of MVD + HAD and MVD + VD resulted in higher retention of nutritional compositions, better antioxidant activity, and lower energy consumption than that of HAD. Furthermore, combined drying processing exhibited similar rehydration capacity but lower hardness compared to that of HAD. [ABSTRACT FROM AUTHOR]

Rice analog is a kind of ready to eat food prepared by twin-screw extruder. Few people study the drying process of wet-extruded foods and the effects of extrusion parameters on product properties based on multi-level. In this research, the experimental investigation of drying was a two-stage procedure: the evaporation of free water rapidly at first and then expansion at high temperature. The influence of the interaction of extrusion parameters on the physiochemical properties was analyzed by using response surface methodology and principal component analysis. Results showed that with regard to microwave drying in the first step, improving drying efficiency, but made the water distribution uneven. The first and second drying had opposite effects on solubility, peak viscosity, and setback of extruded products. This impact of feeding speed was most evident in hardness. Temperature was the most predominated factor for residence time, final viscosity, waterholding capacity, hardness, adhesiveness, and chewiness. The influence of interaction of extrusion parameters to the properties of rice analogs was orderly. Except for the interaction between feeding speed and screw speed, chewiness was influenced deeply by other interactions. The pasting properties were negatively correlated with elasticity, cohesion, and adhesiveness, but positively correlated with compression work. The adhesiveness had a good reference for optimizing processing parameters and control the properties of extruded foods. [ABSTRACT FROM AUTHOR]

The aim of the study was to evaluate the influence of different drying methods on physicochemical parameters of 3 saskatoon berry cultivars: 'Honeywood', 'Smoky' and 'Martin'. Convective drying (CD), microwave-vacuum drying (MVD) and combined drying (CD/MVD) significantly affected moisture content, water activity and colour. Among polyphenolic compounds, 10 flavan-3-ols, 7 anthocyanins, 8 phenolic acids and 11 flavonols were identified by the UPLC-PDA-Q/TOF-MS system in dried saskatoon berries. The total content of identified polyphenolic compounds present in dried saskatoon berries ranged from 21.4 to 66.3 g/kg dry matter, for respectively 'Martin' and 'Smoky'. The strongest ability of extracts to scavenge ABTS radical cations was noted for 'Honeywood', followed by both 'Smoky' and 'Martin'. Antioxidant capacity of products was connected with the content of polyphenolic compounds. 'Honeywood' and 'Smoky' can be best recommended for the production of dried merchandise. The microwave vacuum drying at 480 W with reduction to 120 W give product with the quality similar to this obtained by freeze drying, especially when it comes to the retention of polymeric procyanidins and flavonols present in the fruit. In conclusion, quality of dried saskatoon berry can be successfully moderated by appropriate selection of drying techniques and parameters. • 38 polyphenolic compounds were identified in dried saskatoon berry. • Similar quantity of polyphenolics can be obtained after microwave vacuum and freeze drying. • Polyphenols of saskatoon berry can be retained by microwave-vacuum drying technique. [ABSTRACT FROM AUTHOR]

In this research, the effect of microwave pre-treatment on qualitative characteristics and sensory properties of air-dried potato stickswas investigated. Different powers (180-900W) and times (1-5 minutes) of microwave were used before air-drying of samples. The moisture content, rehydration, shrinkage, browning, colour indices and sensory properties (taste, colour, shape, strength, and total acceptance) of potato samples were evaluated after the drying process and the response surface method (RSM) was used to determine the optimal conditions for the microwave treatment. Used for the highest levels of physicochemical and sensory properties. results showed that, with increasing the power and time of the microwave oven resulted in an increase in the moisture content, shrinkage, rehydration and total colour change of the samples. Sensory evaluation results showed that in the microwave pre-treatment, only the scores of the taste and colour of potato sampleswere influenced by the microwave power and time. According to the results of optimization by the surface response method, the power of 180Watts and the time of 3.5 minutes for the microwave pre-treatment were introduced as optimum conditions. [ABSTRACT FROM AUTHOR]

Hot air drying (HAD) at temperatures below the spontaneous evaporation temperature could be combined with microwave (MW) radiation as a thermal energy source in order to reduce the drying time. A photon flux in the microwave range interacts with dipolar molecules (water) through orientation and induction, producing electrical energy storage and thermal energy accumulation and generating an increase in the internal energy of food. The different mechanisms involved in water transport could change when the microwave penetration depth exceeds the sample characteristic dimension of mass transport. The aim of this paper is to determine the effect of MW in the combined HAD-MW drying of raw potato in order to obtain the real driving forces and mechanisms involved in the water transport, with the purpose of optimizing the MW power used. For this purpose, combined drying was carried out on potato samples (0, 4 and 6 W/g). The sample surface temperature was monitored by infrared thermography, and the sample mass was measured continuously through a precision balance. In parallel with continuous drying, another drying treatment was performed at different times (20, 40, 60, 90, 120, 180, 420 min) and conditions (0, 4 and 6 W/g) to analyze the dielectric properties, mass, moisture, volume and water activity. The results show that it is possible to monitor combined drying by infrared thermography, and it can be concluded that the convection heating is mostly transformed into surface water evaporation, with negligible thermal conduction from the surface, and microwave radiation is mostly transformed into an increase in the potato’s internal energy.

The aim of this study is to find a better drying method to replace conventional hot air drying (HAD) in terms of faster, energy efficient and better product quality. Two alternative drying techniques, microwave combined with hot air drying (MHD) and microwave vacuum drying (MVD), are compared in this study to dry peeled and destoned longan fruit. Both MHD and MVD reduced the drying time up to 48 % and energy consumption as compared to HAD. These techniques provided lower product redness, yellowness and shrinkage but higher lightness and porous structure as compared to HAD. MVD reduced hardness and toughness of the dried product. MHD provided the highest preference score in terms of colour and shape and was as acceptable as the commercial product dried by HAD. MHD is the most suitable method for longan drying. [ABSTRACT FROM AUTHOR]

The aim of this study was to select an appropriate drying technique from air-impingement jet drying (AIJD), hot air drying (HAD) and microwave drying (MWD) which can be combined with freeze drying (FD). Results showed that AIJD with relatively high efficiency, low energy consumption and good drying quality was suitable to be combined with FD. To further improve the drying technology of kiwifruits, the energy consumption and quality of dried kiwifruit with different conversion point during combined FD and AIJD were also tested. The energy consumption obtained for AIJD+FD and FD+AIJD was lower than that obtained for FD alone. Among the products, the kiwifruit processed by AIJD+FD not only showed better attractive green colour and higher sweetness perception, but also revealed higher rehydration ratio than FD and FD+AIJD kiwifruits, which was positively related to microstructure changes. The best AIJD+FD process, from nutrient retention and antioxidant activity considerations, was the combination of 65 min AIJD pre-drying and FD finish drying. Therefore, AIJD pre-drying and FD finish drying as a promising way with short drying time and strong nutrient retention capacity may be applied to the drying processing of agricultural products. [ABSTRACT FROM AUTHOR]

The aim of the present study was to evaluate and compare different drying methods (microwave, hot air + microwave, and osmotic dehydration + microwave) in raspberries (cv. Heritage). A portion of raspberries was pretreated with osmotic dehydration (60°Brix sucrose solution at 20°C for 360 min) and another with hot air drying (HAD) (1.5 m/s air speed at 60°C for 300 min). Pretreated raspberries were then dried by microwave and at three different intensities (3.5, 7.5, and 11 W/g). Physicochemical properties (moisture content, water activity, and drying rate) and quality parameters (optical properties, mechanical properties, antioxidant capacity, and rehydration capacity) of dried raspberries were evaluated. Results showed that the microwave drying (MWD) at 7.5 W/g (50 min and final temperature of 79 ± 5.1°C) allowed a high yield of dried raspberries. The combined processes were not efficient to accelerate the decrease of moisture content, due to the low drying rate of the pretreatments. In terms of quality, none of the drying processes allowed a high retention of the antioxidant capacity. However, they allowed an appropriate rehydration performance. The combination of HAD with MWD allowed obtaining a good appearance and desirable texture on the dried product. Thus, this last option seems to be the best among the drying methods tested, but additional studies are required to improve the efficiency of the process and the effect on the antioxidant capacity during drying. [ABSTRACT FROM AUTHOR]

The drying of coal slime with high moisture content is indispensable for the majority of its industrial applications. In view of the low drying rate at the falling-rate drying period during the conventional drying process, hot-air drying followed by microwave drying, a featured deep drying method, can fundamentally solve this problem and achieve fast and efficient dewatering. In this study, the combination of hot-air and microwave drying to dry coal slime was presented, the general behavior of combined drying method was investigated at a combined fixed bed reactor with hot-air in the temperature range of 120–200 °C and a microwave oven with a maximum power of 800 W. The critical point of hot-air drying, also termed transition point at which hot air drying switched into microwave drying, were experimentally determined and the results showed that the moisture contents of the critical points were about 15% for the samples used. Furthermore, the effects of different target moisture contents and microwave powers on the drying performance and energy consumption of combined dewatering were studied. The results showed that microwave drying could significantly elevate the drying rate when the coal slime reached the critical moisture contents during the hot-air drying method, which indicated that combined drying was an effective method to achieve deep drying of coal slime with a significant reduction in total drying time. [ABSTRACT FROM AUTHOR]

Physicochemical quality parameters of plum powders obtained by applying conventional drying methods and their combination devised to process plums were evaluated. The effect of freeze-drying (FD), vacuum drying (VD), convective drying (CD), microwave-vacuum drying (MVD) and combination of convective pre-drying and microwave finish-drying (CPD-MVFD) affected physical (bulk density, porosity, colour, solubility) and chemical (polyphenolic compounds determined by UPLC and antioxidant capacity by TEAC ABTS and FRAP methods) properties of plum powders. The MVD at 1.2 W g −1 and a novel combination for plum powders production – CPD-MVFD at 70 °C/1.2 W g −1 allowed the best preservation of phenolic compounds and increased the efficiency of production. Results obtained support the use of MVD and its combination for better quality of dried plum products. The study proved that the determination of the browning index and HMF level (formed via Maillard reaction) might be good tool for monitoring the thermal processing of plum powders. [ABSTRACT FROM AUTHOR]

In this work, we examined and compared two combined alternatives for the drying of blueberries (O’Neal). Pretreatments of osmotic dehydration (60°Brix sucrose solution at 40°C for 6 h) and hot air drying (HAD) (60°C, 2.5 m/s for 90 min) were performed to reach the same water content. Pretreated blueberries were then dried by microwave at different microwave output power values: 562.5, 622.5, and 750 W. The combined drying processes were also compared with HAD alone (control). The effects of the processes over blueberries were studied in terms of decrease in water content, drying rate (DR), mechanical properties (firmness and stiffness), optical properties (L*,a*, and hue angle (h)), antioxidant capacity, and rehydration capacity. The hot air–microwave drying decreased the process time and presented a high drying rate compared with the osmotic dehydration–microwave processes and the control drying. In terms of quality, the antioxidant and rehydration capacities were the most affected. The results showed that the best drying method to obtain the desired final product was the hot air–microwave drying (750 W). [ABSTRACT FROM PUBLISHER]

High energy consumption during freeze drying (FD) is a major concern that limits its application on common food product manufacturing. In this research, fresh duck egg white protein (FDEWP) powder and desalted duck egg white protein (DDEWP) powder were obtained by a combined two-stage tandem drying technologies (FD and microwave–vacuum drying [MVD]) in order to reduce energy consumption while maintaining good product quality. The results showed that the drying time for the FDEWP and DDEWP powders was significantly decreased by FD + MVD compared to those obtained by the FD-only process. The FDEWP powders dried by FD + MVD had a better color (higherL* and lowerb*), lower apparent density, and lower foaming stability but higher emulsifying index than those dried by FD only. The DDEWP powder dried by FD + MVD had a product quality similar to that of FDEWP powder, suggesting that the DDEWP powder could be widely used as a food ingredient. [ABSTRACT FROM AUTHOR]

Grape leaves (Vitis vinifera L.) weighing 50 g (±0.08) with a moisture of 4.08 kg(moisture) kg-1 (dry matter) (75.35% wb) were dried using three different drying methods: microwave, air and combined microwave-air. Drying continued until the leaf moisture decreased to 0.14 (±0.01) kg(moisture) kg-1 (dry matter) (9.07% (±0.20) wb). Drying periods lasted 5-11, 30-70 and 1.5-6 min for microwave, air and combined microwave-air drying, respectively, depending on the drying level. In this study, measured values of moisture were compared with values of predicted obtained from several thin-layer equations; the Alibas Model was found to have the best fit. The optimum drying period, color and ascorbic acid content were obtained by using the combined microwave-air drying method with the optimum combination of 500 W of microwave power at a temperature of 75°C. [ABSTRACT FROM AUTHOR]

The influence of the hot air drying (HAD) and the hybrid drying (microwave drying followed by HAD) with (MWODHAD) or without (MWHAD) previous osmotic dehydration (OD) was evaluated on the effective moisture diffusivity (D eff), volumetric shrinkage (Sh), rehydration, carotenoid content and color of sliced carrots. The OD was performed with a ternary solution of sucrose and sodium chloride (35 °C; 300 min). The HAD procedure was carried out at 70 °C (1.5 m/s) and the MWHAD was tested using three different power levels (55.7, 167.9, 336.8 W) until the final moisture content of 0.13 ± 0.01 kg H 2 O/kg dry matter (DM). The results showed that the use of MWHAD with the highest power, reduced (p < 0.05) the total drying time (144 min) and increased the D eff compared to the HAD. Moreover, the MWHAD treatment showed the highest values of Sh, rehydration and carotenoid content. The sliced carrots dried using these three drying arrangements had no significant differences in color. In general, the combined treatment MWHAD could improve the drying rate and the quality. • Innovative technologies utilization in the production of dried carrots was studied. • Hybrid drying reduced drying time in comparison to hot-air drying. • Microwave power level laded increase effective moisture diffusivities. • Osmotic dehydration prevented the shrinkage. • MWHAD presented less degradation of carotenoids. [ABSTRACT FROM AUTHOR]

Dependency of absorbed power by microwave on the local moisture content in a glass particle layer was measured with a new method; that is, heating the wet layer. The heating experiment was performed using a laboratory-scale combined convective and microwave heater/dryer that was manufactured by modifying a domestic microwave oven at 2.45 GHz. The measured result was strongly dependent on the local moisture content and showed a maximum and a minimum within the measured range of the moisture content. This dependency can be explained by the assumption that moisture in the wet layer behaves as a mass of the free water. The combined drying rate of the wet layer measured with the heater/dryer was simulated with both the power dependency and the experimental convective-only drying rate. Power dependency on temperature is as important as the moisture content in the simulation. Simulated results agree very well with experimental ones. [ABSTRACT FROM AUTHOR]

• Six drying methods (HAD, FD, MVD, VD, MVD + VD, MVD + HAD) were used to dry cabbages. • Different drying methods had significant influences on quality of dried cabbages. • Combined drying methods showed better nutrient retention than individual HAD. • MVD + HAD products showed higher rehydration capacity compared to that of HAD. • MVD + HAD performed more uniform honeycomb porous structure than individual HAD. Cabbag has been considered as one of attractive raw materials for dehydrated vegetables owing to high nutrient value. However, information about how drying methods affect the physicochemical properties of cabbage is limited. In present study, segmented cabbages were subjected to freeze drying (FD), hot air drying (HAD), microwave vacuum drying (MVD), vacuum drying (VD), MVD combined with HAD (MVD + HAD) and VD (MVD + VD). Dehydrated cabbages were compared in terms of nutritional components, antioxidant activity, microstructure, texture and so on. Results demonstrated that HAD conducted a worse effect, with loss rate of nutritional components >45%. However, two combined methods performed higher retention for nutritional compositions, better antioxidant activity and lower energy consumption than individual HAD. Furthermore, MVD + HAD products exhibited higher rehydration capacity and more uniform honeycomb porous structure but lower hardness compared to HAD. This conclusion would be fundamental for choosing more appropriate drying methods to obtain desirable quality. [ABSTRACT FROM AUTHOR]