Wheat is one of the most vital staple crops in the world. Its milling process is one type of physical operation using extrusion-induced fragmentation. This study aims to explore the influence of the kernel morphological structure on its mechanical behavior under compressive loads using X-ray micro-computed tomography (micro-CT) modeling and finite element analysis (FEA). The research subjects were selected as wheat kernels with a moisture content of 16%. Accurate three-dimensional (3D) models were constructed for the simulation. The milling parameters were optimized for highly precise and low-loss wheat processing. A texture analyzer was employed to capture the stress-strain curves of the wheat kernels. Different morphological types were utilized under the ventral and lateral compression modes. These curves were used to determine the relationships among kernel morphology, elastic modulus, compressive strength, and ultimate load. The results show that the minimum elastic modulus and compressive strength were calculated as 35.15 and 5.57 MPa, respectively in the largest kernel type (A1). Large-grained wheat also exhibited a higher limit load during extrusion, indicating a stronger resistance to deformation. In contrast, the small-grained wheat shared the lower limit load more prone to rupture under relatively lower loads. Furthermore, the ultimate load reached 59.62 N under ventral compression, which was significantly higher than the 50.44 N observed under lateral compression. Therefore, the minimum extrusion load of 59.62 N was recommended for the full fragmentation of the wheat kernel in industrial milling. Three-dimensional geometric models of the wheat kernels were reconstructed using micro-CT scan data and reverse engineering techniques. Subsequently, the optimal models were imported into the FEA software. The distribution of the stress and strain fields was then simulated to clarify the total deformation behavior under compression. Simulation results indicated that the ventral groove region exhibited the most significant concentration of stress and strain, indicating the primary structural vulnerability during loading. In contrast, the equatorial plane was identified as the key governing region for the propagation of deformation throughout the kernel. Furthermore, the crack propagation paths in micro-CT images demonstrated that the high degree of spatial consistency with the high-stress regions was predicted by FEA simulation. In the ventral and lateral compression modes, the cracks were consistently extended inward along the longitudinal axis of the ventral groove. The initiation and propagation areas of these cracks closely matched the simulated regions of the maximum stress concentration. The high alignment between experimental observations and simulation validated the reliability and effectiveness of the model with micro-CT imaging. The mechanical behavior of the wheat kernels was also obtained to integrate the micro-CT imaging and FEA simulation. A robust model was also provided to accurately simulate the internal stress. The deformation mechanisms of wheat kernels under compression offered valuable theoretical insights for the milling industry. The grain morphology was highlighted to determine the structural role of the ventral groove and equatorial plane, particularly the mechanical response of the kernels. Such insights were crucial to refine the milling strategies, in order to minimize the structural damage for the high yield and nutritional integrity. Ultimately, the findings can greatly contribute to the theoretical models and engineering design for the optimal parameters of wheat milling. The key areas of the stress concentration were identified as the mechanical response of the kernels under various loading. The finding can also provide the scientific foundation to improve the milling efficiency, energy saving, and nutritional quality of wheat products.

Bioactive ingredients such as polyphenols and carotenoids have various health benefits such as anti-cancer and antioxidant activities. However, bioactive components are unstable and easily damaged in the gastrointestinal environment, making them unable to fully exert their functional effects. Proteins and polysaccharides can form complexes via non-covalent or covalent interactions, which have been widely used as encapsulation materials to enhance the stability and activity of bioactive compounds. This review summarizes the types of protein-polysaccharide complexes, and describes the application of the anti-solvent, pH-driven, thermal gelation and emulsification methods for the delivery of bioactive ingredients by protein-polysaccharide complexes. It is anticipated that this review will provide a reference for the research and application of bioactive compounds encapsulated in protein-polysaccharide complexes.

The combination of vacuum freeze drying (FD) and hot air drying (HAD) has been observed to markedly reduce the volumetric shrinkage of hot air dehydrated products. While the FD can be attributed to concurrently optimizing energy consumption. However, the appearance quality of combined drying materials is still unstable at present. This study aims to clarify the shrinkage mechanism of apple products during the FD-HAD. Four points of moisture transition (moisture contents of dry basis were 1.00, 0.76, 0.53, and 0.33 g/g, respectively) were selected for the combined drying of apples. Shrinkage, texture, microstructure and pore distribution were determined in the dehydration products. The water migration and distribution of the samples were analyzed at the HAD stage using low-field nuclear magnetic resonance (LF-NMR). The results showed that the shrinkage of FD-HAD samples was significantly (P<0.05) better than that of HAD ones. The moisture transition point shared a significant (P<0.05) effect on the shrinkage of the samples (6%-45%). There was no outstanding volumetric shrinkage when the moisture content at the transition point was below 0.53 g/g. The samples were more shrinkable, harder and less crisp, as the moisture content increased at the transition point. There was a great variation in the center collapse. The decrease was found in the porosity and average pore size, with the increase of moisture content at the transition point. FD-HAD treatment saved energy more substantially (23.58%-28.95%), compared with the FD. The unit energy consumption decreased gradually with the increase of water content at the conversion point. The shrinkage of the sample in the FD-HAD occurred in the HAD when the moisture content at the conversion point was greater than 0.53 g/g. The sample was divided into two phases of rising and falling in the HAD, where the volumetric shrinkage of the sample mainly occurred in the rising phase. A three-phase transition of water was found in the sample from the ice crystals to the liquid and water vapor, which was then removed from the sample. There was a rapid decrease in the free water, and little change was measured in the content of bound and immobile water. There was a larger humidity difference between the center and the surface of the sample. The water was migrated from the center to the surface. The ice crystals inside the sample were basically removed by sublimation, and then to reduce the melting of ice crystals, when the moisture content at the transition point was less than 0.53 g/g. The small amount and range of free water and its migration resulted in a small shrinkage of the sample. In summary, the controllable transition point of co-drying controls shrinkage can be expected to reduce the amount and extent of ice crystal melting, as well as the free water migration in the HAD phase of the sample. There was less damage to the microscopic pores caused by moisture migration. This finding can provide the basic data and theoretical reference for the precise regulation of the appearance quality of FD-HAD samples and energy saving.

Freeze drying and combined freeze drying-microwave vacuum drying can be required for high-quality dried products, due to the long processing time, high energy consumption and equipment cost. In this study, three schemes of microwave power loading were used for the multiphase microwave drying (MMD) of Chinese yam. A systematic investigation was implemented to clarify the effects of conversion point moisture content on a dry basis (0.36, 0.59, and 0.79 g/g) on the drying performance and quality of dried products. Freeze drying, microwave freeze drying and microwave vacuum drying were used as the control. Some parameters were also evaluated on the drying performances, energy consumption, rehydration ratio, shrinkage ratio, color, hardness, crispness, and microstructure of Chinese yam. The results showed that the MMD scheme Ⅰ, Ⅱ, and Ⅲ reached the critical temperature at 300, 240, and 210 min, respectively. The evaporation stage arrived when the material temperature reached the critical temperature, at which the conversion point moisture content on a dry basis for MMD schemes I, II, and III were 0.36, 0.59, and 0.79 g/g, respectively. The energy consumption of drying Chinese yam using MMD was reduced by 68%-70%, and 34%-38%, respectively, compared with the FD and MFD. The MMD drying rate of Chinese yam increased with the increase of microwave power level, whereas, the energy consumption decreased. There was an increase in the conversion point moisture content and shrinkage on a dry basis, whereas, the rehydration decreased. The hardness was much larger than before, leading to the broken cell structure of Chinese yam. MMD scheme Ⅰ (conversion point moisture content on a dry basis 0.36 g/g) entered the evaporation stage with the lowest moisture content. The internal pore channels of the material formed a stable skeleton in the sublimation drying stage. A porous structure was maintained in the evaporation drying stage, indicating better rehydration. The drying time of the MMD scheme Ⅰ was reduced by 31.3%, compared with the microwave freeze drying. The energy consumption was lowered by 68% and 34%, respectively, compared with the freeze drying and microwave freeze drying. The dried Chinese yam products were obtained with a uniform porous structure and superior quality. There was no significant difference in the rehydration capacity (2.44±0.04), shrinkage ratio (0.88±0.02), color, hardness (4.95±0.45) N, and crispness (2.48±0.51) N, compared with the microwave freeze drying. The shrinkage rate of MMD scheme Ⅲ was significantly lower than that of schemes Ⅰ and Ⅱ. This was because the higher the moisture content at the conversion point was, the more microwave energy absorbed. The greater deformation of material was formed in the subsequent drying, due to the combined heat and moisture migration. The outstanding honeycomb structure was obtained after freeze-drying Chinese yam, indicating the best rehydration and quality, and the lowest shrinkage but with a relatively high energy consumption. Microwave vacuum drying with low energy consumption shared the lowest rehydration, the most severe shrinkage and cell structure collapse. Multiphase microwave drying can be used to serve as the Chinese yam, according to the requirement of high product quality, efficiency and energy-saving drying. The microwave loading scheme can be adjusted for the multiphase microwave drying of Chinese yam. The moisture content can be controlled on a dry basis at the conversion point at a suitable level. The high-quality Chinese yam can be produced similarly to the quality FD products.

Eucommia ulmoides male flowers contain various biologically active substances, such as phenylpropane compounds, cyclic ether terpenes, lignans, and flavonoids. Eucommia ulmoides male flowers also share the antibacterial, anti-inflammatory, analgesic, anti-aging, anti-fatigue, antiviral, anti-mutagenic, anti-tumor, immune-enhancing, sedative, weight-reducing, blood pressure-lowering, and central nervous system-stimulating functions. However, the content of high moisture in flowers has made them susceptible to browning and rot, thus limiting their economic and medicinal application. Therefore, Eucommia ulmoides male flowers need to be dehydrated promptly after harvesting, in order to better preserve their nutritional value. However, there are no studies on the most suitable drying for Eucommia ulmoides male flowers as raw materials. The current research aims to fill this research gap. Five drying methods were also selected as vacuum freeze drying, microwave vacuum freeze drying, hot air drying, far infrared radiation drying, and heat pump drying. Fresh Eucommia ulmoides male flowers were used as the study object. A systematic investigation was made to explore the effects of different treatment methods on the quality characteristics, volatile components, and energy consumption. The results showed that microwave vacuum freeze drying was the most efficient, requiring only 6 hours, 57% less time than vacuum freeze drying. Color analysis revealed that the vacuum and microwave vacuum freeze drying shared the larger L* values (49.20 and 47.99, respectively) and smaller total color differences (ΔE), 5.34 and 5.74 respectively. There was also very similar to the fresh Eucommia male flowers. Scanning electron microscopy revealed that smoother surface morphologies were observed in the samples that dried by vacuum and microwave vacuum freeze drying. But there were the outstanding wrinkles in the rest. In terms of antioxidant capacity, the samples after microwave vacuum freeze drying presented the strongest DPPH free radical scavenging ability (94.74 mg/g) and ferric-reducing antioxidant power (39.63 mg/g). The ABTS free radical scavenging of the samples treated under microwave and vacuum freeze drying was significantly higher than that of the rest. Additionally, 27 compounds were detected in the volatile components. Among them, microwave vacuum freeze drying produced the most volatile components with 18 kinds, the number of 1.8 times in the fresh Eucommia ulmoides male flowers. Correlation analysis was also performed on the types, content, and antioxidant capacity of volatile components in Eucommia ulmoides male flowers before and after drying. There were varying degrees of correlation between L* and the content of geniposidic acid, chlorogenic acid, and aucubin, as well as their free radical scavenging. While there was no significant correlation with the types of volatile components. Lastly, a comparison was conducted on the energy consumption required for different drying methods. The vacuum freeze drying required the least energy consumption, whereas, the microwave vacuum freeze drying required the least. In conclusion, the drying dominated the significant impact on the quality characteristics and volatile components of Eucommia ulmoides male flowers. Therefore, the most suitable drying was set as the microwave vacuum freeze drying. The reason was that the drying time and energy consumption were reduced to effectively maintain the quality and volatile components of Eucommia ulmoides male flowers. This finding can provide valuable insights for the application of microwave vacuum freeze drying, particularly for the drying processing, innovation, and utilization of Eucommia ulmoides male flower products in food and medicine industries.

This study aims to accurately predict the distribution of heat and moisture in maize piles during ventilated drying. Taking the maize pile within the silo as the subject, the heat and moisture transfer model was established to simulate the ventilated drying of the corn. A systematic investigation was also implemented to clarify the suitable ventilation conditions. The heat was then released by maize respiration, according to the local thermal non-equilibrium equation. The experiment was carried out on the integrated silo of grain drying and storage using COMSOL Multiphysics. An experiment was conducted on the maize pile in the silo, with specific conditions, including air velocity, air temperature and relative humidity. The simulation was focused on the moisture content, temperature distribution of maize and temperature, humidity distribution of air in the maize pile. The results showed that the heat and moisture transfer model effectively simulated the ventilated drying of maize pile in the silo. The relative errors between the simulated and experimental values of maize temperature and moisture content at four points within the silo ranged from 1.4%-12.1% and 0.3%-14.5%, and the average relative errors were 4.8% and 6.5%, respectively. Similarly, the relative errors between the simulated and experimental values of air temperature and air relative humidity within the silo were 0.7%-15.1% and1.3%-15.4%, respectively, and the average relative errors were 5.5% and 8.9%, respectively. Notably, there was the unevenness of maize in the silo at the initial stage of maize ventilation. The inner layer of maize was experienced the higher rates of heating and drying. The higher air velocity resulted in the increased airflow per unit time. For example, the maximum difference in the moisture content reached 0.03 g/g along the ventilation direction. However, the heating and drying rates of maize were gradually reduced, as the ventilation progressed, leading to a decrease in the unevenness of maize pile. The equilibrium temperature of maize was then reached after 25 h, while the approximate equilibrium moisture content was reached after 60 h. The air temperature rose rapidly within the first hour of ventilation, followed by a slow increase to nearly 25 °C. The humidity initially increased and then decreased, where the rate of decline was gradually slowed down until equilibrium was reached. The cloud map analysis revealed that there was a significant difference in the area near the silo wall and the overall, indicating the need to optimize the silo and ventilation structure. The air velocity had also enhanced the heating and drying rate. But after reaching 0.16 m/s, there was a further increase in the air velocity without considering the change rate of corn. The relative humidity shared little effect on the trend and value of maize temperature. But the relative humidity decreased the drying rate, whereas increased the equilibrium moisture content of corn. The higher air temperatures resulted in a higher drying and heating rate with a lower content of equilibrium moisture. According to the maize temperature and moisture content under different conditions, the combination of ventilation parameters was achieved in the air relative humidity less than 75%, air velocity of 0.09-0.23 m/s, and air temperature with atmospheric conditions. The relative errors between the simulated and experimental values of the moisture content of maize in the pilot test of ventilated drying ranged from 1.3% to 16.7%, with an average value of 4.4%, indicating the further practicality of the constructed model. Then the moisture contents of the maize in the innermost, middle, and outermost layers approached the safe moisture content around 130, 180, and 250 h, respectively. The unit energy consumption of ventilated drying of maize was 890.2 kJ/kg, which was remarkable for energy saving. The quality indexes also showed the feasibility of ventilated drying and storage of high-moisture corn. Therefore, change-over ventilation and grain circulation were recommended in practical production, in order to improve the unevenness of temperature and humidity of the maize pile. These findings can also provide valuable theoretical support to optimize the corn-ventilated drying.

Microstructural evolution can often dominate the macroscopic shrinkage and deformation of plant-based food materials. It is very essential to clarify the evolution pattern of pore structure during drying, in order to evaluate the microstructural variations in the materials. Taking Chinese yam as a raw material, this study aims to investigate the conversion of the dehydration process during multiphase microwave drying. The samples of Chinese yam were also obtained under different drying schemes (Scheme 1, 2, and 3, i.e., microwave power densities of 0.1, 0.5, and 0.9 W/g). The microwave power density (0.1, 0.5, and 0.9 W/g) was adjusted at the drying stage of the second sublimation (after 90 min of drying, recorded as sublimation-II). X-ray microcomputed tomography (μCT) was used to visualize the internal structure of Chinese yam. The properties of samples were then acquired for the shrinkage ratio, pore structure, and pore size distribution. The results showed that the time required to reach the critical temperature at the phase transition point for the samples in Schemes 1, 2, and 3) was 195, 155, and 145 min, respectively. At the transition point, the sample of Scheme 1 exhibited the lowest water content (26.16%), the highest open pore rate (57.1%), and the highest number of pores. Furthermore, the smallest volume change of the samples was also observed during evaporation drying. Therefore, the lower microwave power density at the sublimation drying stage effectively reduced the moisture content of the sample at the transition point. Additionally, the open pores were formed to minimize the outstanding shrinkage that occurred in the sample. The sample exhibited a greater number of pores and a smaller volume change during evaporation drying. The open porosity in sublimation-II was reduced by 8.02% and 12.16%, respectively, for Schemes 2 and 3. Subsequently, the higher moisture content of the samples resulted in damage to the pore structure during sublimation drying. There was a notable reduction in the porosity of the samples. The pore diameters of the samples exhibited a non-normal distribution in the three drying schemes. An increasing trend of pores with diameters less than 20 μm was also observed in Schemes 1 and 2. In contrast, the tiny pores in the samples of Scheme 3 continued to decrease with drying, while the number of large pores increased. This trend was related to the larger microwave loading. The equivalent diameters of connected pores in the dried samples exhibited a reduction of 3.08%, 8.37%, and 20.04%, respectively, in three drying schemes, compared with the transition point. There was no significant difference (P > 0.05) in the mean diameter and volume of non-connected pores in the samples at the sublimation drying stage among the three drying schemes. In the samples with the higher water content at the transition point (Scheme 2 and 3), the removal of moisture resulted in a significant increase (P < 0.05) in the equivalent diameter of non-connected pores at the evaporation drying stage. The μCT analysis revealed that there were no significant variations in the internal structure of the sample in Scheme 1, the removal of more moisture at the sublimation drying stage was facilitated to form the more robust pore structure inside the samples. There was no impact of water removal on the microstructure of the samples during evaporation drying. These findings can provide empirical evidence and theoretical insights to efficiently process high-quality dehydrated fruits and vegetables by multiphase microwave drying.