Influence of drying method and temperature profile on the volatile, structural, and mechanical quality attributes of dried strawberries

SummaryThe production of good quality of instant mung bean vermicelli was investigated using microwave vacuum drying (15, 22.5, or 30 W g−1) and microwave continuous drying (70 Hz). Microwave vacuum drying could generate larger and greater porosity than microwave continuous drying. Vermicelli dried at 30 W g−1 had the shortest rehydration time (2.14 min) and the best cooking quality. Microwave drying provided greater lightness (L*), greenness (a*) and yellowness (b*) for the dried vermicelli and a greater blueness (b*) for the cooked vermicelli. The tensile strength of each vermicelli product was not significantly different, while the elasticity of the commercial vermicelli was higher than other samples. Interestingly, the general acceptance of vermicelli dried at 22.5 and 30 W g−1 reached 7.03 and 7.00, respectively, on a 9‐point hedonic scale and was higher than commercial vermicelli. In conclusion, microwave vacuum drying could be advantageously applied in the instant mung bean vermicelli production process due to its short drying and rehydration times and the high acceptability of the final product.

A batch-type microwave vacuum dryer was used to study the effects of different microwave power densities on the drying characteristics and quality of whole lychee (Litchi chinensis Sonn.) fruits. Lychees were treated at different power levels and it was observed that the drying process included two drying stages when power density was above 0.3 W/g, and drying process was consisted of three drying stages when power density was 0.1 W/g. The optimal power density was found to be 0.6 W/g. A typical pulp temperature profile of lychees was found during microwave vacuum drying (MVD), including four stages: increasing, decreasing, gently increasing and sharply increasing. Moreover, the decrease in quality was negatively correlated with an increase in temperature at every stage in the temperature profile. Temperature control was applied to improve the quality of MVD lychees. The optimal temperature range value in terms of drying time, vitamin C content, bulk density and sensory evaluation was found to be 60–65C. Practical Applications Air-dried (AD) lychees are popular as traditional food in South China and its sales volume was about 80% of all processed lychee foods. AD lychees have deep brown pulp with much shrinkage and poor flavor. However, microwave vacuum drying (MVD) could produce high-quality dried lychees with light golden yellow color, less shrinkage, better taste, shorter drying time and lower energy. The information provided in this work will sever as the basis for further mass production. MVD lychees are much more promising as a snack food than AD lychees.

Effects of microwave vacuum drying on drying characteristics, bioactive components, antioxidant capacity, and starch structure of germinated red adzuki beans

It is demonstrated that the vertical profile of gradient Richardson number, Ri, can be shaped by control of the working-section inlet temperature profile. In previous work (Hancock and Hayden in Boundary-Layer Meteorol 168:20–57, 2018; 175:93–112, 2020; 180:5–26, 2021) the inlet temperature profile had been specified but without control of the profile of Ri in the developed-flow region of the working section. Control of the inlet temperature profile is provided by 15 inlet heaters (spread uniformly across the height of the working section), allowing control of the temperature gradient over the bulk of the boundary layer, and the overall temperature level above that of the surface. The bulk Richardson number for the 11 cases covers the range 0.01–0.17 (there is no overlying inversion). In the upper approx 2/3 of the boundary layer the Reynolds stresses and turbulent heat flux are controlled by the gradient in mean temperature, while in the lower approx 1/3 they are controlled both by this gradient and by the level above the surface temperature. In three examples, Ri is approximately constant at 0.07, 0.10 and 0.13 across the bulk of the layer. The previous observation of horizontally homogenous behaviour in the temperature profiles in the top approx 2/3 of the boundary layer but not in the lower approx 1/3 is repeated here, except when, tentatively, Ri does not exceed 0.05 over the bulk of the boundary layer. Favourable validation comparisons are made against two sets of local scaling systems and field data over the full depth of the boundary layer, over the range 0.006 le Ri le 0.3, or, in terms of height and local Obukhov length, 0.005 le z/L le 1.

This study investigates the combined effects of magnetic fields, buoyancy forces, porosity, rotation, and Joule’s heating on fluid flow and heat transfer dynamics. The analysis is performed using a numerical approach, with the system oriented along three axes: the z-axis aligned with the plate, the y-axis perpendicular to the plate, and the x-axis orthogonal to the y-z plane. An infinite plate extends along the x and z axes, with a uniform transverse magnetic field applied parallel to the y-axis. By employing the finite difference method in MATLAB, we explore how various dimensionless parameters influence temperature and velocity profiles. Our findings reveal that an increase in the local temperature Grashof number enhances primary velocity while reducing secondary velocity near the fixed end. Temperature profiles show a decrease near the plate, increasing further away. The study also highlights that a higher Joule heating parameter leads to elevated primary velocity and temperature profiles but diminishes secondary velocity. Additionally, increasing rotational parameters is observed to decrease both primary and secondary velocities while augmenting temperature profiles near the plate. These results underscore the significant role that magnetic fields, rotational effects, and Joule heating play in modulating fluid flow and thermal behavior. The insights gained from this study can inform the design and optimization of engineering systems where control of velocity and temperature profiles is critical.

The aim of this study was to determine the effect of microwave power during the vacuum–microwave drying (VMD) on sour cherries in terms of drying kinetics, including the temperature profile of dried material, as well as on some quality factors of the finished product including phenolic compounds, antioxidant capacity, and color. The content of phenolic compounds, antioxidant activity, and color change were used as quality indicators of dried sour cherries. Sour cherries were dehydrated by convective drying (CD) at temperatures of 50 °C, 60 °C, and 70 °C and by VMD at the initial microwave power of 240 W, 360 W, and 480 W reduced to 240 W and 120 W in order to avoid a rapid increase in temperature at the critical moisture content of ca. 1 kg/kg dry mass. Control samples were prepared by freeze drying (FD). The increase in air temperature during CD as well as the increase in material temperature during VMD deteriorated dried product quality in terms of the content of phenolic compounds, antioxidant activity, and color, which was consistent with anthocyanins content. However, VMD turned out to be much better than CD and competitive to FD. The best quality of the dried product and its more attractive color were achieved at VMD at 480 W followed by drying at microwave power reduced to 120 W, which corresponds to anthocyanins content. In addition, the drying process had a positive impact on contents of quercetin and keampferol derivatives. Dried sour cherries have a long shelf life and therefore may be a fine alternative to fresh fruit all year round.

On control of whole temperature profile in an autothermal tube-cooled fixed bed catalytic reactor

Characterization of vacuum microwave, air and freeze dried carrot slices

A new approach to plasma profile control in ITER

Real-time measurement and feedback control of ion temperature profile and toroidal rotation using fast CXRS system in JT-60U

Relative importance of local and regional controls on coupled water, carbon, and energy fluxes

Influence of microwave vacuum drying on glass transition temperature, gelatinization temperature, physical and chemical qualities of lotus seeds.

Apple cubes of 15 mm were dried naturally without adding any chemical preservative using various drying methods namely intermittent hot air–dehumidified air drying with cyclic temperature profile and step-up temperature profile, heat-pump-assisted (HP) drying, convective vacuum-microwave (C/VM) drying, and heat pump vacuum-microwave (HP/VM) drying. The drying kinetics of apple samples dehydrated by different methods was divided into characteristic drying periods and fitted with empirical models, which gave high value of determination coefficient. The application of C/VM in drying of fruits gave the shortest drying time compared to other drying methods (about 50 % of the total drying time). The drying time was affected by effective diffusivity ranging from 3.522 × 10−8 to 1.431 × 10−6 m2/min depending on the drying technique used. It was found that combined drying which apply vacuum microwave (C/VM, HP/VM) gave the lowest values in hardness and chewiness. In addition, HP/VM drying gave the highest retained total polyphenol content, antioxidant activity, and the best appearance quality.

Two drying methods of cranberries (microwave-vacuum and microwave-convective) are reviewed, and their advantages and disadvantages regarding the quality of dried product and the process performance are presented. Mechanically and osmotically pretreated berries were subjected to drying and quality evaluation. Quality parameters are color (in Hunter L*a*b* coordinates), textural characteristics (toughness and Young's modulus), and organoleptic properties (color, texture, taste, and overall appearance). Special emphasis was given to the energy performance of the process, monitoring of the real-time temperature profile, and the total microwave power-on time. Two microwave power densities are assessed, as well as different microwave power-on/power-off cycling periods. In almost all observed parameters, microwave-vacuum drying exhibited enhanced characteristics when compared to microwave-convective drying. Drying performance results (defined as mass of evaporated water per unit of supplied energy) showed that microwave-vacuum drying is more energy-efficient than microwave-convective. Tasting panel results exhibited slight preference in all parameters for microwave-convective dried samples.

34. Ordentliche Mitgliederversammlung der VHD