# The Effect of Hybrid Drying Methods on the Quality of Dried Carrot
## 4 Discussion
[3] also indicated that hot air-dried products are often characterized by unattractive physical appearance, excessive shrinkage, and hard texture. The drying process causes physical changes in the dried material. One of the fundamental but unfavorable changes is shrinkage, which results from the reduction of the volume of the product by the evaporation of a large amount of water. The volume change is accompanied by a change in shape and the amount of evaporated water affects the hardness of the material, therefore the obtained dried material may crack and deform, which adversely affects the final quality of the obtained product. The studies conducted by [PERSON] [42] showed that shrinkage and water content were highly dependent on each other, e.g., the level of shrinkage depends on the water content that is removed during drying. The highest value of shrinkage was characteristic for convection-dried carrots 68.95%. A similar result was obtained by [PERSON] et al. [41] for carrot convective-dried, and by [PERSON] and [PERSON] [43]. Furthermore, [PERSON] et al. [44] observed that for carrots convective-dried the shrinkage was the highest, which may be related to the longer drying time, leading to a higher collapse of the cellular structure of the material. In the research of [PERSON] et al. [45] on the influence of various drying methods, the shrinkage of convection-dried carrots was also the highest. In a convection-dried carrot, the following relationship was observed: the higher the shrinkage, the higher the density, and the lower the porosity. Carrot microwave-dried obtained a similar shrinkage value to convective-dried, which was confirmed by [PERSON] et al. [44], who explained that it can be attributed to large heat generation and more effective removal of moisture, which can cause damage to the cell structure, and shrinkage. The use of freeze-drying allows for obtaining the dried material with lower shrinkage and better retention of the shape and size of the sample. Combined drying can be used as an alternative to freeze-drying because the shrinkage is similar and the use of combined drying methods allows for a significant reduction in drying time. Changes in the porosity of plant material are classified as physical changes taking place in the dried material. This parameter describes the number of voids in the material structure. Porosity is defined as the pore volume compared to the volume of the entire material. This parameter plays an important role in the mass transfer process and also determines the mechanical properties and texture of the food. Porosity increases during the drying process and its value are influenced by the type of raw material used [46]. The highest porosity was shown for freeze-dried carrots, while the lowest was for convective-dried. The high porosity in the freeze-dried sample may result from the fact that this material had the lowest water content among other dried samples, which was removed in the greatest amount during freeze-drying, and low shrinkage. Such quality of the product makes it also demanding in terms of storage conditions. The porous structure contributes to the increased absorption of water and water vapor, therefore the freeze-dried material should be stored in conditions of limited access to moisture [47]. The combination of freeze-drying with convection-drying or microwave-drying allows for a lower porosity of the dried material than freeze-drying. Freeze-drying and microwave-drying increased carrot porosity compared to the microwave-dried sample. For microwave-dried carrot water loss, material shrinkage resulted in less porosity. The results of density, shrinkage, and porosity were confirmed by tissue structure investigations in the microscope. Carrot convection-dried has regularly distributed pores, with similar size and high-density clusters presented which confirm high shrinkage and low porosity value. The freeze-dried carrot is characterized by a large number of small pores which influence the high porosity of the freeze-dried sample.