Understanding the drying mechanism of straw substrate culture block: Physicochemical properties, pore structure, and drying optimization

As a new type of agricultural waste block substrate utilization, the initial wet base state of the substrate culture block needs to be dried. Therefore, studying the drying mechanism of substrate culture block is critical. In this study, the substrate culture block in a dry state was taken as the research object. Based on physical and chemical properties, the internal section of the substrate culture block was characterized by scanning electron microscopy and the pore condition of the particles was quantified. The results showed that the internal pore structure was uniform and favorable for plant root growth. Based on the pore structure, pore channel modeling was constructed to investigate the distribution of the internal multiphase medium and to distinguish between channels and pore-blind channels. The applicability of the modeling was verified and discussed. By measuring the drying rate of the substrate culture block and classifying its drying stages as fast speed, constant speed, and slow speed, it is clarified that the forms of moisture existence are bound-state water and free-state water, and the moisture migration is prioritized as surface adsorption water, interparticle water, particle attached water, and capillary water. Innovate a method to quantify the change of pore space in the drying process by pore coefficient ratio to evaluate the drying quality. The results show that when the pore coefficient ratio is about 40 %, its moisture content is 20 %∼30 %, and the drying effect is best at this time. The physical drying test further confirmed the correctness of the conclusion of the drying stage division and water loss law. This study can provide a theoretical reference for the modeling study of the pore structure of the block matrix and the exploration of its drying mechanism.

Effects of ultrasound-assisted cooking on the physicochemical properties and microstructure of pork meatballs

This research aims to investigate the effect of different ultrasonic powers cooking on the quality of pork meatballs. Pork meatballs treated with ultrasound-assisted cooking at 450 W had the most uniform and smooth structures displayed by scanning electron microscopy. Furthermore, with increasing ultrasonic powers, the water retention capacity of pork meatballs first increased and then decreased, compared with the non-ultrasound group, when the ultrasonic power was 450 W, the cooking yield of pork meatballs increased from 82.55% to 92.87%, and the centrifugal loss decreased from 25.35% to 11.52%. Additionally, ultrasound-assisted cooking had a positive effect on the moisture migration, tenderness, and sensory property of pork meatballs, and 450 W sample exhibited the highest overall acceptability score (P < 0.05). In conclusion, the physicochemical properties and microstructure of pork meatballs could be improved by appropriate ultrasonic power, and ultrasonic technology was considered as an effective processing method for improving the quality of meat products.

Evaluation of moisture migration characteristics of permeable asphalt pavement: Field research

To analyse the moisture migration characteristics of permeable asphalt pavement (PAP) in engineering applications, a PAP sample with a length and width of 163 m and 12 m, respectively, was designed and paved. The pavement comprised PAC-13, PAC-20, ATPB-25, graded grade, and sandy soil subgrade from the top to the bottom. Moisture sensors were set at 4 cm, 10 cm, 28 cm, 46 cm, 61 cm, 76 cm, 101 cm, 126 cm, 176 cm, and 226 cm below the pavement surface to ascertain the volumetric water content during and after rainfall. This data were used to analyse the changes in the infiltration depth, infiltration rate, water level height, and water emptying time of the PAP under different rainfall conditions. The results show that the prediction model for the infiltration depth can be established using the water adhesion rate and rainfall. According to the moisture changes of the pavement layer after rainfall, the water migration process of the PAP can be divided into the drying stage, wetting stage, emptying stage, and recovery drying stage. The relationship between the average rainfall intensity and the average infiltration rate is a linear function. The water emptying time at the depth of 0-10 cm is less than 20 h, and the emptying time at a depth below 10 cm is less than 6 d.

Analysis of macro and micro freezing characteristics of gravelly soil

To investigate the mechanism of effect of different gravel contents on freezing characteristics of gravelly soil, macroscopic and microscopic experiments were combined. Unidirectional freezing experiment and NMR experiment were conducted on gravelly soil, with gravel contents of 0%, 10%, 20%, 30%, 40% and 50%. In unidirectional freezing experiment, final temperature, stratified moisture content and frost swelling of the samples showed a parabolic pattern with an upward opening about the gravel admixture. Among that, it was at the lowest point of 30% content with the closest space between gravel and soil grains, the least consumption of heat conduction, the largest compression of water migration, making the slowest development of frost-heaving and water supply. NMR experiment results showed that freezing characteristic curve was divided into four stages of subcooling-fast-slow-stable freezing, and gravel content was proportional to the subcooling temperature and value of sudden drop of unfrozen water. Combined with the T₂ spectrum, it could be seen that larger pore structure of 30% content was relatively stable with well-distributed water migration during freezing process, and order of water freezing was free water went ahead of bound water, leading to a reduction rate of water migration was from fast to slow, with a consistent pattern of the evolution rate of macro parameters. In summary, the addition of a reasonable gravel proportion in engineering applications of cold zone could ensure relatively well-distributed and stable soil properties and pore structure, and relative low difference in temperature, moisture pooling, and frost swelling. Ultimately improving the safety and reliability of the overall operation of the project.

Moisture migration driven by the electric field causes the directional differentiation of compost maturity

Electric field-assisted aerobic composting (EAC) has been recently believed as a novel and effective process for the resource utilization of organic solid waste. However, the effect of electric field in composting process needs to be further clarified. Herein, moisture migration and compost maturity along electric-field-direction (from anode to cathode) in EAC was first to be explored. It was found that moisture content and compost maturity changed regularly from anode to cathode. At the end of composting, the moisture content of S3 (cathodic zone) was 30% and 62% higher than that of S2 (middle zone) and S1 (anodic zone), respectively. The germination index (a key parameter for compost maturity) in S3 (138.92%) was significantly higher than that of S2 (104.98%) and S1 (84.45%). However, temperatures in S3 were lower than that of S1 and S2, indicating the moisture content played a more important role than temperature for compost maturity in EAC. Furthermore, the microbial activities in S3 were also higher than that of S1 and S2, supporting the trend of compost maturity. This pioneering study demonstrates the electric field can drive moisture gradient migration to control the directional differentiation of compost maturity, showing a great application potential in aerobic composting.

Dynamics of heat transfer and moisture in beef jerky during hot air drying

The aim of this study was to investigate the surface temperature, moisture migration, muscle shrinkage and microstructure of beef jerky during hot air multi-stage drying. Temperatures were sequentially increased from 40 to 50 to 60 °C, and corresponding times were 0.5 h - 1 h - 2.5 h, 0.5 h - 2 h - 1.5 h, 1 h - 1 h - 2 h and 1 h - 2 h - 1 h in 4 groups. With increasing temperature, moisture content and diffusivity of the sample decreased, the surface temperature, moisture migration, muscle shrinkage and the gaps (spacing) between muscle fibres increased. The jerky in groups 3 and 4 attained high overall acceptability. The jerky dried at 40 °C for 1 h, 50 °C for 1 h and 60 °C for 2 h had highest quality. The results cover the range of temperature and time used in beef drying and can be used to optimize the drying process of beef.

Physicochemical and structural changes in myofibrillar proteins from porcine longissimus dorsi subjected to microwave combined with air convection thawing treatment

The effect of microwave combined with air convection thawing (MAT) on the properties and tertiary structure of myofibrillar proteins (MPs) from porcine longissimus dorsi muscle was investigated and compared with single treatments (air thawing, microwave thawing) and fresh meat (FM). Among the thawing treatments, the carbonyl content, dityrosine content, and surface hydrophobicity of MPs in MAT were the lowest, whereas the total sulfhydryl content, water-holding capacity, and Ca²⁺-ATPase activity were the highest, suggesting that MAT retained MPs properties better. MAT possessed a more stable tertiary structure and exhibited slight changes in MPs aggregation and degradation. There was an insignificant difference (P > 0.05) in the immobilized water and free water between the MAT samples and FM, indicating a tighter interaction between water and muscle protein in MAT. Thus, MAT could retain the physicochemical and structural properties of MPs, which provided a combination of thawing treatments for application in meat industry.

Optimization of processing technology using response surface methodology and physicochemical properties of roasted sweet potato

The study evaluated the optimal condition for roasting sweet potato using response surface methodology. Proximate composition, antioxidant activity, volatile compounds, and water migration of roasted sweet potato were also determined. The results revealed that the optimal roasting condition included a roasting time of 40 min, a roasting temperature of 235 °C, and a roasting speed of 40 rad/min, the reducing sugar and vitamin C of roasted sweet potato obtained under optimal condition was 47.79 g/100 g (DW) and 60.25 mg/100 g (DW), respectively. After roasting, starch, protein and vitamin C content of sweet potato were significantly decreased, while total phenolic content and antioxidant activity were increased. 2-Methyl butanal was the main aromatic compound. Low-field NMR indicated that the proportion of free water increased and relaxation times (T₂) were decreased after roast process, indicated that the bound water in sweet potato was diffused from inside to outside, thus the texture became softer.

Dynamics of moisture diffusivity in solid triacylglycerol matrices

The effects of lipid formulation in combination with two crystallization conditions, shearing and non-shearing, on the mechanism of water diffusivity were investigated. Five formulations of lipid which varied in fatty acid compositions, solid fat particles, and emulsifier levels were assessed at 5, 20, and 30°C. Polarized light microscopy was used to study microstructural properties of the samples under dynamic and static conditions; and their moisture permeability was examined using gravimetric technique (ASTM E-96). All formulations and crystallization techniques were confirmed to have a large impact on the crystallization properties and dynamics of moisture migration. Dynamic crystallized samples showed altered structures with different patterns of crystalline clusters. Different values of water diffusivity suggested that shearing affected moisture diffusivity of the samples differently. This effect of shearing was more pronounced in the presence of lecithin. A higher migration rate was observed in sheared samples that contained higher amount of long chain saturated fatty acids.