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Drying is one of the most effective methods to preserve foods and guarantee their supply for more people. Mathematical modeling is an important tool that aids the design, development, optimization and control of food drying systems. Driven by the increasing needs to dry more foods with higher efficiency, sustainability, better food quality and safety, various novel drying technologies have been developed, and food drying modeling approaches have also evolved significantly. In this review, progresses and advancements in empirical, mechanistic, and machine learning (ML) modeling approaches in food drying processes toward Multiphysics, multiphase, multidimensional, and intelligent directions are overviewed. Several challenges, needs, and future trends are identified and discussed, which includes multiscale modeling, shape change and structure deformation, coupling of food reaction kinetics, intelligent control and digitalization, translation, and dissemination of modeling results. The materials presented here aim to emphasize the importance of food drying modeling for addressing the key food challenges and attract more food scientists and engineers to contribute to improve food drying models and a more sustainable food production system. [ABSTRACT FROM AUTHOR]

Postharvest blanching and drying of industrial hemp (Cannabis sativa L.) by infrared (IR) and hot air (HA) heating was studied. Experiments were conducted at different IR heating times (1 and 2 min) and HA temperatures (65 and 85 °C) and compared with conventional indoor drying. Drying time was decreased from 3366 min (conventional) to as low as 222 min (85 °C HA). IR and HA processing reduced the total aerobic bacteria, and total yeast/mold levels by up to 0.81 and 1.85 log CFU/g, respectively from their initial levels of 4.63 and 4.75 log CFU/g, meanwhile reduced the activities of polyphenol oxidase and peroxidase by up to 91.7% and 66.7%, respectively. More than 96.1% total cannabidiol was preserved by thermal processing. Total terpene retention ranged from 18.3% to 71.1% under tested conditions with distinct terpene profiles. The results provide important information on the microbial safety and a timely solution to improve the postharvest processes of hemp. [ABSTRACT FROM AUTHOR]

A nonequilibrium multiphase moisture and heat transfer model was developed to simulate the drying of a single walnut under hot air heating. The walnut was modeled as a 3-layer sphere by differentiating the shell, kernel, and an air gap between them. Drying characteristics of walnuts at 43, 55, 65, and 75 °C under 1.4 m/s air velocity were simulated using finite element method. The simulation results agreed well with experimental data, and the model showed good predictability for drying of walnuts with different initial moisture contents and dimension characteristics (Radj3 > 0.996 for moisture and Radj3 > 0.983 for temperature). The spatial distributions of liquid moisture, water vapor, and temperature in the walnut were determined through model simulation, which provided important information for understanding the mechanisms of heat and moisture transfer during walnut drying process. Findings from this study established theoretical basis for improving the walnut drying process and determining the suitable drying conditions. [ABSTRACT FROM AUTHOR]

In current work, the effects of drying temperature (60, 65, 70, and 75 °C), vacuum pressure duration (VPD; 6, 9, 12, and 15 min), and ambient pressure duration (APD; 2, 3, and 4 min) on drying kinetics and quality attributes of kiwifruit slices during pulsed vacuum drying (PVD) were explored. An artificial neural network (ANN) model combined with a comprehensive method was applied to evaluate the optimal drying condition. Results showed that drying parameters significantly affected the drying kinetics, color, and vitamin C content of kiwifruit slices except for rehydration ratio. The shortest drying time, i.e., 432 min, was obtained at a drying temperature of 75 °C, VPD of 12 min, and APD of 3 min. The lowest total color change (ΔE) occurred to dried products at 65 °C, VPD of 12 min, and APD of 4 min. The vitamin C content of dried product decreased with the increase of APD. The optimal condition predicted by ANN was 65 °C, VPD of 12 min, and APD of 2 min, which obtained the highest comprehensive score of dried kiwifruit slice. The relative error percentage between the predicted and experimental compressive score at optimal condition was 2.92%. [ABSTRACT FROM AUTHOR]

The objective of current work was to develop a new pilot-scale pulsed vacuum infrared drying (PVID) system for the drying of berries. The system design and drying performance evaluation for grape and goji berries are reported here. The PVID system consisted of three major sections, including infrared heating section, vacuum section, and a controlling section. Electrical infrared (IR) emitter was made with carbon fiber sheet at the thickness of 2–4 mm, which emitted IR wavelength of 1–30 μm. The control system was used to achieve paused pressure by switching the drying chamber pressure between atmospheric pressure (101 kPa) and vacuum (3–10 kPa) successively and maintaining the pressure for different time periods. Grapes and goji berries were dried in a single layer at three different temperatures (55, 65, and 75 °C) with an atmospheric duration ranging from 1 to 12 min and vacuum duration from 10 min to constant vacuum. The drying characteristic and quality of PVID dried berries were investigated and compared with that of hot air (HA) dried berries. Results showed that the IR heating temperature, atmospheric duration, and vacuum duration had significant effects (p <.05) on the drying time. The optimum drying conditions for grapes and goji berries were IR heating at 65 °C, vacuum duration of 15 min, and atmospheric duration of 4 and 2 min, respectively. The corresponding drying time is nearly 720 min for grapes, and 450 min for goji berries. The PVID dried grapes and goji berries had more attractive color than that of HA dried ones. These findings demonstrated that PVID should be a promising method to produce high-quality dried berries. This study laid a good foundation for scaling up the technology in the future. [ABSTRACT FROM AUTHOR]

Fresh harvested walnuts are dehulled, washed, and then dried by hot air (HA) as a continuous process in the industry. The objective of the current work was to study the walnut structure and investigate its effect on the moisture transfer characteristics during the walnut soaking and drying processes. Moisture transport pathways into the walnuts were determined using fluorescence tracer approach, and the hydration kinetics of walnuts under different soaking temperatures (15, 25, and 35 °C) was studied using Peleg model. HA drying experiments in single layer in a self-designed automatic HA dryer at 43 °C and air velocity of 1.41 m/s. The influence of the stem pore (sealed and non-sealed) and the soaking process (0, 2- and 5-min soaking time) on the walnut drying characteristics were investigated systematically. The results indicated that both the presence of the stem pore and the soaking time had significant influence (p < 0.05) on the hydration and drying characteristics of walnuts. Moisture absorptions through the stem pore and the shell were equally important during the soaking process. Two to five minutes soaking process led to 2–4 h additional drying time. This study contributed valuable knowledge for the simulation and prediction of moisture transfer characteristics during the walnut soaking and drying processes. The findings from this study could potentially be applied to the walnut drying industry for more efficient processing [ABSTRACT FROM AUTHOR]

The objective of this research was to examine the drying characteristics of pulsed vacuum drying (PVD) system as an alternative drying technology for a functional food—Poria cocos. Poria cubes in thin layer were dried at different temperatures (55, 65, and 75°C), vacuum duration (5, 15, and 25 min), and atmospheric pressure duration (4, 8, and 12 min) to evaluate the operating conditions on the drying kinetics and quality attributes of P. cocos. The quality attributes included volume shrinkage ratio, firmness, water-soluble polysaccharide content. Volume shrinkage ratio was determined by image processing technology and analyzed by Bigot’s curves. The material internal temperature was also recorded during the whole drying process. Considering the drying rate and quality attributes, drying temperature of 65°C, vacuum pressure duration of 15 min, and atmospheric pressure duration of 4 min were proposed as the most favorable drying conditions for drying Poria cubes. The current work indicates PVD is a promising technology for P. cocos drying as it not only enhances the drying process but also improves the quality attributes of it. [ABSTRACT FROM AUTHOR]

The drying characteristics of yam slices under different constant relative humidity (RH) and step-down RH levels were studied. A mass transfer model was developed based on Bi-Di correlations containing a drying coefficient and a lag factor to describe the drying process. It was validated using experimental data. Results showed that the drying air with constant RH levels of 20, 30, and 40%, temperature of 60°C, and air velocity of 1.5 m/s had an insignificant effect on drying time. This phenomenon was likely attributed to the fact that higher RH led to a rapid increase in sample’s temperature. The higher sample temperature could provide an additional driving force to water diffusion and thereby promote the moisture movement, which could minimize the negative effect of lower the drying rate in the initial drying stage. Applying air with 40% RH for 15 min in the initial stage achieved the desired color and reduced the drying time by 25% compared to the drying time under continuous dehumidification from an initial RH of 40%. Using the developed Bi-Di correlation, the estimated Biot number, effective moisture diffusivity, and mass transfer coefficient ranged from 0.1024 to 0.1182, 1.1133 × 10−10to 8.8144 × 10−9 m2/s, and 1.8992 × 10−9to 1.7364 × 10−7 m/s, respectively. A rather high correlation coefficient of determination (R2between 0.9871 and 0.9971) was determined between the experimental and predicted moisture contents. The present findings contribute to a better understanding of the effect of relative humidity on drying characteristics. The developed Bi-Di correlation provided a new method to determine the effective diffusivity of moisture in drying. [ABSTRACT FROM PUBLISHER]