Search

Freezing pretreatment is one of the novel pretreatments for fruit and vegetable drying, and its treatment intensity has a direct impact on the effectiveness of color protection and drying promotion. However, there are major limitations on transformations of dynamic changes of and water status of material, which is crucial for judging processing intensity. Here a mathematical model was presented to characterize heat transfer in freezing pretreatment of carrot crisps. The model accounts for freezing phase change heat transfer. And a further analysis on the effect of freezing pretreatment on product quality was made according to experimental results. Results showed that the heat transfer process of freezing pretreatment is divided into four stages based on the temperature changes, namely fast cooling segment, phase transition segment, secondary cooling segment, constant temperature holding segment. In the phase transition segment, the presence of latent heat is the core element that the temperature of the material can be maintained constant. In the constant temperature holding segment, the effect of processing time on the material was significant. The optimal pre‐freezing conditions for carrots was a temperature of −15°C for the duration of 45 min plus an additional 10 h, resulting in dried products with minimal color difference, maximum rehydration ratio, and optimal puffing degree. [ABSTRACT FROM AUTHOR]

A drying device based on infrared radiation heating technology combined with temperature and humidity process control technology was created to increase the drying effectiveness and quality of sea buckthorn. Based on the conventional k-turbulence model, the velocity field in the air distribution chamber was simulated using COMSOL 6.0 software. The airflow of the drying medium in the air distribution chamber was investigated, and the accuracy of the model was verified. Given that the inlet of each drying layer in the original model had a different velocity, the velocity flow field was improved by including a semi-cylindrical spoiler. The results showed that installation of the spoiler improved the homogeneity of the flow field for various air intakes, as the highest velocity deviation ratio dropped from 26.68% to 0.88%. We found that sea buckthorn dried more rapidly after being humidified, reducing the drying time by 7.18% and increasing the effective diffusion coefficient from 1.12 × 10−8 to 1.23 × 10−8 m2/s. The L*, rehydration ratio, and vitamin C retention rate were greater after drying with humidification. By presenting this hot-air drying model as a potential high-efficiency and high-quality preservation technology for sea buckthorn, we hope to advance the development of research in the sea buckthorn drying sector. [ABSTRACT FROM AUTHOR]