Microstructural study of apple slices during hot air-explosion puffing drying

In order to reveal the change laws of microstructure in apple slices during hot air-explosion puffing drying, the microstructure images and parameters of apple slices under different drying conditions were obtained by using paraffin sectioning, microscopic observation, and image processing techniques with apples as raw material and CO2 as drying medium. Subsequently, the changes in internal cell and pore structure of dried apple slices were analyzed, as well as the relationship between micro-parameters of apple slices and macro-measurement indicators was further obtained. Results indicated that the overall cross-sectional area, cross-sectional perimeter, equivalent diameter, and porosity of cells increased by explosion puffing drying, while the cell roundness and wall roughness factors changed relatively little. Meanwhile, macro-micro parameters of expanded apples were fitted and analyzed. Then, the obtained mathematical model showed a nonlinear correlation as experimental and predicted results exhibited good agreement, with determination coefficients R2 more significant than 0.8, which could better expect the macro-microparameters to change in the drying process. The results of this research could provide an essential reference for exploring the change laws of tissue microstructure parameters in apples dried by hot air-explosion puffing drying, with expansion and rehydration ratios under different experimental conditions, as well as optimizing the puffing drying process and designing corresponding drying equipment.Practical ApplicationsFresh apples have high moisture content and are not easy to store, so drying is usually used to reduce the moisture content to extend shelf time and increase economic benefits. For the drying process of fruit and vegetable products, scholars mainly focused on the influence of microstructure parameters on moisture migration, drying rate, heat and mass transfer and other factors, but did not give a quantitative description of how microstructure parameters affect macroscopic parameters. In this article, the relationship between microstructural changes and macroscopic indicators was investigated by taking puffed apple slices as an example. Research could provide an essential reference for exploring the change laws of tissue microstructure parameters in apples dried by hot air-explosion puffing drying, with expansion and rehydration ratios under different experimental conditions, as well as optimizing the puffing drying process and designing corresponding drying equipment. This study reveals the change laws of microstructure in apple slices during hot air- explosion puffing drying, the experimental results agree well with those predicted by the mathematical model, which could provide important reference for optimizing the puffing drying process and designing the corresponding drying equipment.image