## 1 Introduction  
Recently, consumers' interest in health-promoting snack products has significantly increased [1]. They are looking for new healthy products, which can be also obtained by modification of existed snacks by introducing changes in recipe as well as technology. One of the most popular group of snacks, mostly consumed by children and young people, are products obtained from extruded pellets later on expanded by frying. The pellets are gained from a variety of components in which starch-based substrates are dominant (including wheat, rice, corn or potato). In recent years, various ingredients, i.e., fruits, vegetables, whole grains and proteins have been incorporated into a formulation used for their preparation. The addition of these ingredients allows one to obtain extruded snacks with improved nutritional and antioxidant composition [2]. A new ingredient, rich in bioactive compounds, with high potential is Jerusalem artichoke tubers. It is a good source of carbohydrates, such as inulin and its derivatives, e.g., fructooligosaccharides [3]. _Helianthus tuberosum_ L. is also a good source of numerous polyphenic compounds [4]. Previously, more than 20 phenolic compounds have been identified in tubers among which chlorogenic acid was a dominant one [5]. Such composition makes the Jerusalem artichoke suitable for the obtainment of functional foods [6]. However, there were few attempts of using Jerusalem artichoke as an ingredient in snacks production. The artichoke flour was used as an additive in corn snacks (obtained by high temperature and short time of extrusion process) and the obtained products were highly ranged [7]. On the other hand, some undesired flavour changes of snacks were noticed. It was suggested that other ingredients may influence the sensory quality of these types of snacks.  
From the technological point of view, snacks obtained from pellets are usually expanded by immersion in hot oil that significantly increases the fat content in ready-to-eat products as well as improve palatability. The fat content, which usually ranges between 20-40%, depends on pellets composition, type of frying oil and frying conditions. Fat is not the only source of flavour and aroma, but it also makes a contribution to the texture and significantly increases the calorific value of the snacks. The quality of fat also influences the storage stability of fried products. Taking both aspects into consideration, some other additives with relatively strong antioxidative properties should be considered in design of modern snacks. Another option of novel snacks processing can be using of non-frying technologies that cause the expansion of products as an effect of application of high temperature without mass transfer. In such treatment, usually hot air or microwaves are used. The microwave heating is a technological process that has a great impact due to its efficiency in the expansion of snack foods [8]. However, the sensory properties of such snacks are modified to a different extent when compared to traditional technologies, thus, the comparison of these expansion methods on the quality of freshly prepared and stored snacks will provide a new insight in novel snacks preparation process. Previously, the concept of fruit powders addition was employed for the preparation of the extruded snacks [9], but only the basic chemical, physical properties and sensory attributes were considered. The products gained were characterised by lower fat and sugar contents and received good level of consumers acceptance which provide an inside into development of novel snacks with improved functional properties. Thus, the study aimed at the evaluation of physical and chemical properties in terms of polyphenics and antioxidant capacity of novel snacks gained from pellets composed of Jerusalem artichoke flour with addition of fruit juice powders (after extrusion) fried or microwaved in order to compare their properties after 5-week storage.