Drying Characteristics and Quality Attributes Affected by a Fluidized-Bed Drying Assisted with Swirling Compressed-Air for Preparing Instant Red Jasmine Rice

Influences of emerging drying technologies on rice quality

Rice is an important staple food in the world. Drying is an important step in the post-harvest handling of rice and can influence rice qualities and thus play a key role in determining rice commercial and nutritional value. In rice processing, traditional drying methods may lead to longer drying times, greater energy consumption, and unintended quality losses. Thus, it is imperative to improve the physical, chemical, and milling properties of rice while preserving its nutritional value, flavor, and appearance as much as possible. Additionally, it is necessary to increase the efficiency with which heat energy is utilized during the thermal processing of freshly harvested paddy. Moreover, this review provides insights into the current application status of six different innovative drying technologies such as radio frequency (RF) drying, microwave (MW) drying, infrared (IR) drying, vacuum drying (VD), superheated steam (SHS) drying, fluidized bed (FB) drying along with their effect on the quality of rice such as color, flavor, crack ratio, microstructure and morphology, bioactive components and antioxidant activity as well asstarch content and glycemic index. Dielectric methods of drying due to volumetric heating results in enhanced drying rate, improved heating uniformity, reduced crack ratio, increased head rice yield and better maintain taste value of paddy grains. These novel emerging drying techniques increased the interactions between hydrated proteins and swollen starch granules, resulting in enhanced viscosity of rice flour and promoted starch gelatinization and enhanced antioxidant activity which is helpful to produce functional rice. Moreover, this review not only highlights the existing challenges posed by these innovative thermal technologies but also presents potential solutions. Additionally, the combination of these technologies to optimize operating conditions can further boost their effectiveness in enhancing the drying process. Nevertheless, future studies are essential to gain a deeper understanding of the mechanism of quality changes induced by emerging processing technologies. This knowledge will help expand the application of these techniques in the rice processing industry.

Mathematical Description of Changes of Dried Apple Characteristics during Their Rehydration

The mathematical description of changes of dried apples characteristics (mass gain, volume increase, dry matter loss, rehydration indices, and colour) during their rehydration was performed. The effect of conditions of both processes on model parameters were also considered. Apple slices (3 and 10 mm) and cubes (10 mm) were dried in natural convection (drying air velocity 0.01 m/s), forced convection (0.5 and 2 m/s), and fluidisation (6 m/s). Drying air temperatures (Td) were equal to 50, 60, and 70 °C. The rehydration process was carried out in distilled water at the temperatures (Tr) of 20, 45, 70, and 95 °C. Mass gain, volume increase, and dry matter loss were modelled using the following empirical models: Peleg, Pilosof–Boquet–Batholomai, Singh and Kulshrestha, Lewis (Newton), Henderson–Pabis, Page, and modified Page. Colour changes were described through applying the first-order model. Artificial neural networks (feedforward multilayer perceptron) were applied to make the rehydration indices and colour variations (ΔE) dependent on characteristic dimension, Td, drying air velocity, and Tr. The Page and the modified Page models can be considered to be the most appropriate in order to characterise the mass gain (RMSE = 0.0143–0.0619) and the volume increase (RMSE = 0.0142–0.1130), whereas the Peleg, Pilosof–Bouquet–Batholomai, and Singh and Kulshrestha models were found to be the most appropriate to characterise dry matter loss (RMSE = 0.0116–0.0454). The ANNs described rehydration indices and ΔE satisfactorily (RMSE = 0.0567–0.0802). Both considered process conditions influenced (although in different degree) the changes of the considered dried apple characteristics during their rehydration.

Effect of Large-Scale Paddy Rice Drying Process Using Hot Air Combined with Radio Frequency Heating on Milling and Cooking Qualities of Milled Rice

The objectives of the study on a continuous flow hot air dryer combined with radio frequency heating at different temperatures (HA/RF) (38 °C, 42 °C, 46 °C, and 50 °C) in a large-scale process compared with conventional continuous flow hot air drying (HA) were (1) to investigate the drying characteristics, drying kinetics, and milling quality of the process and (2) to observe the cooking quality and compare the sensory differences of the cooked rice after treatment. The drying characteristics and moisture diffusivity showed that the higher the radio frequency (RF) heating temperature, the shorter the drying time. The specific energy consumption and energy cost decreased when the RF heating temperature increased. The optimal condition in terms of fissure percentage was HA/RF42. In addition, there were no significant differences in head rice yield and white rice color determination, amylose content, texture profiles, and pasting properties in all HA/RF treatments. In the triangle test, it was found that at least 6% of the population could perceive a difference between HA and HA/RF50. In conclusion, this study proposes the further development of the HA/RF drying process at low-temperature profiles and shows the great potential of RF technology for commercial drying in rice industry.

Quality of Milled Rice from Large-Scale Dried Paddy Rice by Hot Air Combined with Radio Frequency Heating

A scaled-up process for paddy drying was developed using hot air (HA) combined with radio frequency (RF) heating. The study was conducted using hot air (control treatment) arranged in descending order in four temperature levels, namely 80 °C at moisture content of 25–26%, 70 °C at moisture content of 20–25%, 60 °C at moisture content of 17–20%, and 50 °C at moisture content of 13–17%, as well as with hot air combined with radio frequency (HA/RF) at different paddy temperatures (45–60 °C) by adjusting the appropriate RF energy when passing through RF heating chamber, namely HA/RF45, HA/RF50, HA/RF55, and HA/RF60. Each treatment was performed in three replicates and data were statistically analyzed in a randomized complete block design. The quality attributes of paddies affected by the drying process were assessed: fissure percentage, color, milling quality, and sensory evaluation. The drying efficiency showed that the drying time and the specific energy consumption could be decreased by up to 54.44% and 23.17% at HA/RF60 and HA/RF45, respectively. As the RF heating temperature increased, the fissure percentage of brown rice kernels at HA/RF45 and HA was not significantly impacted. Regarding color evaluation, combining RF heating and convective drying at all given conditions could be statistically applied in terms of the b*, WI, and ΔE* value. Considering the milling yield of HA as the baseline, head rice yield was maximized at HA/RF45, while bran yield reached the maximum at HA/RF60. The liking score of cooked rice after it was dried using the HA method was the highest. This study concludes that the HA/RF45 was the most appropriate drying condition, and this may provide preliminary exposure to the industrial drying of paddies.