###### Abstract  
A comparative study was conducted on the effect of vacuum impregnation and drying methods on the production of dried sweet potatoes with high bioactivity. The present study determined the quality and physicochemical properties of dried sweet potato depending on the used impregnating solutions. Sweet potatoes were pretreated in freshly squeezed onion (O) and kale (K) juice, onion and kale (OK) mixture (1:1), and sodium chloride solution. Vacuum impregnation (VI) was carried out under reduced pressure (6 kPa) for 2 min, after which the impregnating solution was dispensed and maintained under vacuum for 4 min. Sweet potato slices were dried using vacuum drying (VD) and freeze drying (FD) methods. Higher content of polyphenols, carotenoids, and chlorophyll, as well as increased antioxidant capacity and higher VOC profile, were recorded for the dried products obtained using the sublimation method. The use of vacuum impregnation reduced the hardness of the products and other textural characteristics, such as cohesiveness, springiness, and gummness. Furthermore, we found that vacuum impregnation pretreatment was a beneficial method for improving the characteristics of dried vegetables. The highest content of phenolics, carotenoids, and chlorophylls in dried sweet potatoes were recorded when samples were impregnated with onion and kale juice. For the fresh sweet potato, the highest contribution in VOC composition had phenylacetaldehyde (44.90%), (E)-2-octen-1-al (9.43%), and benzaldehyde (8.18%), respectively. The interesting content of VOC profile compounds in dried sweet potatoes was recorded when samples were impregnated with kale juice. sweet potato; phenols; antioxidant activity; VOCs; vacuum impregnation; freeze drying; vacuum drying +
Footnote †: journal: Applicand Ap  
have shown that the best radical neutralization capacity of dried materials is obtained by the FD method [6; 7; 8]. Dried products obtained by this method showed levels of polyphenolic compounds and antioxidant activity that were comparable to those of the raw material [9]. The low temperature of the FD process slows the degradation reactions of bioactive compounds and preserves higher nutrient values compared to other drying methods [2]. Lowering the temperature of the convection drying process can have a positive effect on the quality of the dried product. Vacuum drying (VD) offers the possibility of lowering the process temperature, owing to the presence of reduced pressure in the drying chamber. VD is often used to dry heat-sensitive materials [10]. Choosing the right drying method and the right process parameters is necessary to obtain a product with a high content of bioactive compounds and high antioxidant activity [1]. Vacuum impregnation (VI) is a widely used vegetable and fruit pretreatment process that involves osmotic dehydration under reduced pressure [11]. VI is considered a promising technique for use in the food industry [12]. Recently, numerous studies have been conducted using micro-organisms and biologically active compounds as impregnating solutions. These activities are aimed at obtaining innovative nutritional products. Researchers noted that, in the case of dried zucchini slices, VI with MD (maltodextrin) and CaCl\({}_{2}\) solutions did not lead to a significant water loss. When using the addition of maltodextrin in impregnating solutions, the authors observed, in dried zucchini thick walls, intercellular spaces rich in solutes and turgid cells, in which no structural changes were observed [13]. The purpose of VI is to introduce additives, such as microbial preservatives, anti-browning agents, or cryoprotectants, into fruit and vegetable tissues. The additives are intended to improve the properties of biological materials [12]. However, there are few reports of product modifications induced by impregnated particles and/or pressure changes affecting the functional and nutritional properties of processed fruits and vegetables [11].