## 1 Introduction  
The United Nations Sustainable Development Goals also apply to food production, and measures to reduce food waste must be taken to reduce water consumption, ensure a reduction in environmental pollution and reduce hunger. This thread of issues is complex, although any action aimed at reducing food waste is extremely valuable. According to the European Commission, based on Eurostat data, 20% of the sum of food produced is wasted [1]. One of the largest groups of food waste is bread. According to the Waste and Resources Action Programme, bread waste accounts for 10% of the total food waste in the UK [2]. In Baltic countries such as Sweden, Poland, and Finland, between 10 and 25% of the bread produced is wasted at various stages of the food chain [3; 4; 5; 6]. One of the ways to reduce the waste of bread is to extend its freshness period. Sourdough bread is less susceptible to staleness, and its period of consumer attractiveness for consumption is extended [7]. It has been reported that the use of sourdough in breadmaking contributes to an improvement in the volume, texture and sensory quality scores of bread, an increase in bread acidity and the amount of low molecular weight dextrins, and an improvement in the bread physical and microbiological shelf life compared to straight doughs [8]. Sourdough production technology is believed to be the oldest biotechnological process used to produce cereal-based foods [9]. Traditional sourdough is made from water and flour by spontaneous fermentation. The constant propagation of microorganisms is maintained by the addition of a new portion of the nutrient medium to the sourdough every day. In this case, flour is mixed with water and added to the leaven. The process of sourdough fermentation should take place at a temperature of 20 \({}^{\circ}\)C to 30 \({}^{\circ}\)C, and if carried out correctly, sourdough with rich microbiota and high metabolic activity is obtained [10]. Many groups of microorganisms enter leaven microbiota; these are mainly lactic acid bacteria (LAB), acetic acid bacteria (AAB), and yeast. In the flour, there could be a presence of bacteria from the Enterobacteriaceae family, as well as the _Staphylococcus aureus_ and _Bacillus cereus_ species, but in the initial phase of fermentation, the environment is quickly dominated by LAB and does not allow the development of pathogenic or spoilage microbiota [11]. The main LAB species in sourdough are, among others, _Limosiactobacillus reuteri, Lactobacillus amyloororus_, _Lactiplantiobacillus plantarum_, _Levilactobacillus brevis_, _Lactobacillus paralimentarius_, _Fructilactobacillus sanfranciscensis_, _Limosiactobacillus fermentutum_, _Lactobacillus curvostus_, _Lactobacillus sakei_, and _Pedicoccus pentosacous_[11; 12]. On the other hand, the main yeast species are _Saccharomyces cerevisiae_, _Kazakhstania humilis_, _Yarrovia keelungesis_, _Toruslapora delbrueckii_, and _Pichia kudriavzevii_[12]. Often overlooked bacteria in the description of sourdough are AAB (mainly _Acetobacter malorum_, _A. pasteurianus_, and _A. lovaniensis_), which have an undoubted impact on the quality and sensory profile of the obtained bread [13; 14]. Such a rich variety of microbiota in sourdough affects its fermentation properties and determine the overall quality of the bread. Bread production with the use of sourdough is a very sensitive method, which depends on various parameters that must be controlled. Most important is the thorough selection of a starter culture with specific and desirable properties for acidification during fermentation, as well as the fermentation temperature. Starter cultures can be defined as microbiological preparations containing a large number of cells of at least one microorganism that cause the fermentation of the product to which they were added, while maintaining stability and microbiological purity, and thus ensuring the safety of the final food product [15].