Sustainable valorization of olive by-products: environmental impact, biotechnological and probiotic approaches for bioactive recovery in alignment with circular bioeconomy.

The olive oil industry generates vast amounts of by-products, including olive pomace, olive mill wastewater, olive pits, and olive leaves, which pose serious environmental and economic challenges. However, these residues are rich in bioactive compounds such as polyphenols, dietary fibers, unsaturated fatty acids, and sugar derivatives, making them valuable resources for sustainable valorization. This review explores innovative biotechnological and probiotic-driven approaches to convert olive waste into high-value products, aligning with the United Nations Sustainable Development Goals (SDGs), particularly SDG 12 (Responsible consumption and production) and SDG 13 (Climate action). Probiotic fermentation has potential to enhance the nutritional and functional properties of olive by-products by biotransformation of phenolics, reducing bitterness, and improving bioavailability. Fermented olive wastes exhibit promising applications in functional foods, animal feed, natural preservatives, and nutraceuticals, offering antioxidant, antimicrobial, and gut health benefits. Additionally, microbial bioconversion enhances the extraction of valuable compounds while minimizing waste generation. This review highlights current advances, key challenges, and future perspectives for integrating probiotic and enzymatic valorization strategies into a circular bioeconomy, promoting sustainable industrial practices and environmental protection.