## 1 Introduction  
Food waste is a global problem, causing significant economic losses around the world and negatively affecting the environment [1]. The problem is deepened by the fact that the world population may reach approximately 10 billion in 2050, resulting in a growing demand for various types of products, especially food [2]. It is estimated that food production, including agricultural production, will increase from approximately 47% to 102% during this time to meet the growing demand for food [3]. However, it should be taken into account that the intensification of food production largely contributes to the degradation of the natural environment. The negative effects of food production include, among others, excessive greenhouse gas emission, associated with increasingly frequent weather anomalies, loss of biodiversity, bioaccumulation of toxic substances, reduction in forest area, and depletion of natural resources [4; 5]. Consumerism also contributes to the intensification of production, which, regardless of social, climatic, or ecological costs, leads to overproduction and generates excessive waste amounts. It is estimated that approximately one-third of food produced is wasted annually on a global scale, which results in social costs (including waste of resources) and negatively affects the financial results of producers [6]. Food waste losses may occur at various stages of the food supply chain, from primary production, including agriculture and animal production, through processing, packaging, and distribution processes, to losses caused by the consumer [7]. Food loss and waste generation depend on the type of food, with greater loss and waste occurring in perishable foods such as fruit and vegetables. However, bakery waste is also a serious global problem. Bread is one of the most important products consumed around the world, and its global production reaches >100 million tons per year. Therefore, it is a commonly wasted food in most developed countries, which is a particularly serious problem in Europe [8]. It is difficult to determine the exact amount of wasted bread, as the use of water and energy in the production and transport process should also be taken into account; however, it is estimated that 10% of all bread produced is wasted worldwide [9]. For example, in the United Kingdom (UK), bread is the second most frequently wasted food. It is estimated that every day in UK homes, the equivalent of 25 million slices of bread or 1,300,000 loaves is thrown away [10]. In Poland, research carried out by the Federation of Polish Food Banks in 2012-2018 indicates that bread is the most frequently thrown-away product, and the percentage of respondents declaring waste of bread ranged from 49 to 62% in this period [11]. Therefore, various ways of using bakery waste are being undertaken towards vaporization into value-added products considering that bread contains a wide range of nutrients. In 100 g of bread, there are approximately 50-70 g of carbohydrates, 8-10 g of protein, 1-5 g of fat, and trace amounts of phosphorus [12]. Bread waste can be used as biomass for the production of biohydrogen, regarded as clean and renewable energy [13], as well as for the production of ethanol, considered one of the most promising fuel sources [14; 15]. [PERSON] and [PERSON] [16] described biogas production from damaged bread. Moreover, bread waste can be used as feed for livestock [17; 18] as well as a substrate for hydroxymethylfurfural synthesis and for the production of pigments, proteins, or aroma compounds [19; 20; 21]. Many researchers emphasize that bakery waste usage should largely focus on processing it into new food products. This is possible to achieve by using the fermentation processes with various microorganisms. Lactic acid fermentation is considered a safe and practical way to acidify food products and extend their shelf life because the metabolites produced and the low pH inhibit the growth of undesirable microorganisms.