# Repurposing Olive Oil Mill Wastewater into a Valuable Ingredi for Functional Bread Production
## 1 Introduction  
Despite numerous efforts in recent years to manage wastes from agricultural activities and food by-products, these residues continue to pose environmental challenges and incur disposal costs for producers ([PERSON] et al., 2016; [PERSON] et al., 2016). Over the past decade, numerous global institutions have called for more sustainable policy choices to address these issues, promoting the circular economy model as a strategy for achieving greater global sustainability ([PERSON] et al., 2016). Ensuring the sustainability of the food production process remains one of the most critical challenges for the future ([PERSON] et al., 2016). In this context, the olive oil industry holds substantial economic importance within the European Union (EU), producing over 6-7 million tons of oil annually ([PERSON] et al., 2016). Olive cultivation is widespread in the Mediterranean basin, with Italy being one of the top producers ([PERSON] et al., 2016). However, the olive sector generates substantial waste. The extraction process results in three by-products: olive paste, the fleshy part of the olive fruit remaining after oil extraction; olive pomace, the primary solid residue left after oil extraction; and olive oil mill wastewater (OOMW), the liquid waste produced during oil production ([PERSON] et al., 2016). While olive paste and olive pomace are typically reused as soil fertilizers or combustible raw materials ([PERSON] et al., 2016), OOMW is more challenging to recycle due to its strong odor, dark brown color, and acidic pH ([PERSON] et al., 2016). Nevertheless, OOMW is rich in bioactive compounds like polyphenols ([PERSON] et al., 2016), which are known for their health benefits ([PERSON] et al., 2016). According to a review by [PERSON] et al. (2016), it contains over 30 biophenols and related compounds with antioxidant properties and potential cardioprotective and cancer-preventive effects. Given the growing need for more efficient and sustainable approaches, innovative non-conventional methods are gaining traction. These methods utilize low-cost raw materials to extract antioxidant compounds, which can be applied in food supply chains, as well as in the nutraceutical and cosmetics sectors. Additionally, the rising consumer demand for nutritionally rich and functional foods has caught the attention of food producers. In this context, cereals and cereal-based products are ideal candidates for fortification, as they are a staple in the daily diet and provide a significant amount of macronutrients and micronutrients, including vitamins and minerals. However, it is important to note that thermal treatments, such as baking and mechanical processes like milling, can significantly reduce or even eliminate dietary fiber and bioactive compounds, potentially diminishing the nutritional value of these products. Therefore, OOMW could be a promising by-product to enhance the positive properties of bread. In addition to its richness in bioactive compounds, it boosts dietary antioxidant levels, often diminished during baking, and introduces unique phytochemicals absent in conventional formulations. Its use supports the development of health-promoting foods, aligns with sustainability and circular economy principles by repurposing polluting agro-industrial waste, and reduces disposal costs due to its high organic load and phytotoxicity. Moreover, OOMW contributes to a more complex and appealing aroma profile through its volatile compounds. Sourdough fermentation is a traditional and widely used technology in Italian bread making ([PERSON] et al., 2016). This process primarily relies on the activity of lactic acid bacteria (LAB), particularly, the heterofermentative species ([PERSON] et al., 2016). While yeasts also play a crucial role, especially in leavening, the presence of LAB is essential for developing the bread's characteristic aroma and extending its shelf life ([PERSON] et al., 2016).