## 1 Introduction  
Food processing leads to inevitable losses. According to a report, \"Food wastage footprint: Impacts on natural resources-Summary report\" [1], fruit processing, packing, distribution, and consumption respectively generate a huge quantity of fruit waste, approximately 1.81, 6.53, and 32.0 million tones worldwide, and most of this is being disposed of either by composting or dumping in landfills, causing environmental pollution [2]. In fruit and vegetable processing, a significant problem is the management or disposal of waste products--the parts not used during technological processing. This is between 10 and 35% of the weight of the processed raw material and includes peel, seeds, and pomace. By-products of fruit processing are created during the production of juices, pulps, and jams. In the juice production process, the pomace mass depends on the pressing efficiency. During traditional pressing, the proportion of pomace is 20-25% of the initial raw material weight [3]. The application of enzyme preparations that liquefy the pulp and the leaching of the pomace with water allows for a reduction in the pomace share to about 12% of the initial fruit weight. Population growth and dietary changes contribute to greater consumption of fruit and vegetables, which in turn results in an increase in the amount of waste associated with their processing. In Europe, by-products from fruit processing account for 8% of all waste from the food sector. In developing countries, the situation is much worse because the by-products of fruit processing are treated as negligible and redundant compared to processed fruit [3]. Other studies indicate the generation of about 50% of by-products during fruit and vegetable processing in the forms of unripe or damaged fruits and vegetables, cores, peels, and pomaces [4; 5]. Poland is an important producer of fruits and products of their processing, such as juices. Such production generates a large quantity of by-products, such as pomaces, that are usually utilized as feed or as raw materials for microbial growth [6; 7]. But from a nutritional point of view, fruit pomaces can be treated as an abundant source of health-promoting components, primarily polyphenols and dietary fiber (DF) [8; 9; 10; 11; 12]. Although pomaces are not expected to be consumed alone, they can be used as a valuable ingredient to extend the health-promoting properties of food. Such an application will allow for the utilization of a by-product, and at the same time, a value-added product will be created. Extruded snacks seem to fit within this objective, and therefore the research has concentrated on the utilization of fruit pomaces as an additive for extruded snacks with an increased level of health-promoting components (polyphenols and fibers) [13; 14]. Extrusion is a high-temperature, short-term physical treatment during which food polymers (usually a cheap one, such as starch or cornmeal) at a relatively low moisture level are subjected to significant structural changes by the combined action of high temperature, pressure, and shear forces. As a consequence, a new product with completely new properties and qualities is created [14], such as breakfast cereals, crisp bread, baby and infant foodstuffs, snack-type foods, meat analogs, textured proteins, noodles, and pasta that could be manufactured in this way [15; 16]. However, starch- or cornmeal-based extrudates are characterized by low nutritional value and thus relatively weak health-supporting properties. Moreover, the extrusion process leads to the loss of polyphenols, i.e., components with broad pharmacological effects [17; 18; 19; 20; 21]. Therefore, it is suggested to supplement raw cereal material with natural or synthetic phenolic compounds or enrich it with vegetables, fruits, or other ingredients before extrusion [17; 22; 23; 24; 25; 26]. It should also be taken into consideration that extrusion gives a great opportunity to utilize raw material products with no previously recognized greater economic importance, such as fruit pomace.