# The Effect of Hybrid Drying Methods on the Quality of Dried Carrot
## 1 Introductions  
Carrots are a vegetable with a pleasant, sweet taste [1]. The only edible part of the carrot is the conical storage root, which is a source of valuable nutrients. The root of garden carrots is orange, red, or purple, depending on the amount of the pigment (\(\beta\)-carotene) [2]. Fresh carrot root consists of 88% water, 10% carbohydrates, and 2% protein with minerals and vitamins. It also contains calcium, phosphorus, potassium, sodium, magnesium, iron, cobalt, zinc, and vitamins, mainly: A, B1, B2, B6, PP, and folic acid [3]. Most of the production of this vegetable is directed at processing, including drying. An important direction of using dried carrots is mixtures of dried spices used in the preparation of meals. In the era of the developing \"fit\" and \"eco\" food trends, dried carrots are also used as a snack for quick consumption, e.g., carrot chips [4]. The reduced amount of water in the material lowers its activity, contributing to the prevention of the development of microorganisms [5], and the products can be stored for a long time without visible signs of deterioration [6]. Moreover, enzymatic and non-enzymatic transformations are reduced [7]. The most commonly used method of drying food is convection heating, which uses air, which is also a factor that supplies heat and removes water from the material [8]. The most important parameter in convection-drying is the temperature, the increase of which causes the acceleration of the drying process. Convection-drying is used to preserve fruit, vegetables, and meat, but high temperature and long process time adversely affect the quality of the obtained products (reduced nutritional value, changes in color, smell,and structure) and convection-drying alone is not a good solution in terms of energy efficiency [9; 10]. Other popular drying methods are freeze-drying, fluidization, and combined (hybrid) methods [11]. Microwave-drying in the food industry uses waves in the 2450 and 915 MHz frequency range. Microwaves interact with the water dipoles of the dried material, due to which hydrogen bonds are broken and energy is released in the form of heat through molecular friction [12]. Due to the high microwave permeability, the product is fully heated with a simultaneous temperature increase [13]. Microwave-drying shortens the processing time, intensifies heat and mass transfer, and lowers costs. It is an alternative to conventional drying methods for a wide range of food products with high water content, such as potatoes, carrots, apples, bananas, and parsley [14]. In addition, it allows the attractive color of products to be maintained and reduces the loss of bioactive ingredients [15]. Freeze-drying is a method that removes water from a previously frozen material by sublimation of ice, omitting the liquid phase [16]. Usually, it takes 24-48 h [17]. Freeze-dried samples are characterized by a porous structure, and preservation of the smell and color of the raw material. The chemical composition of the freeze-dried material slightly changes, especially when it comes to vitamins, micro and macro elements [18]. The disadvantage of the process is the high costs related to the duration and complex apparatus, therefore alternative drying methods are sought to maintain the high quality of the product [19]. Researchers have started to investigate the potential of combining more than one drying technique. This has led to the development of hybrid drying technologies [20]. Combined (hybrid) drying is a method of combining simple drying techniques into one complex process, e.g., convection, microwave, freeze-drying, and ultrasound. The number of drying methods used in combination is not specified [21; 22]. The technology of combining several drying methods is relatively new, constantly improving and developing. The techniques used during combined drying concern: the method of heat transfer, multi-stage, and multi-process drying, and using other treatments in addition to drying, e.g., filtration, and agglomeration.