Olive mill wastewater (OMWW) is a highly complex matrix derived from olive oil extraction, containing phenolic compounds, lipids, minerals, and organic acids. Hydroxytyrosol (HT), an outstanding antioxidant and health-promoting phenolic compound, has garnered significant interest as a natural preservative and functional ingredient. Enzymatic hydrolysis, utilizing purified enzymes to cleave glycosidic or ester bonds, and microbial bioconversion, employing whole microorganisms with their intrinsic enzymes and metabolic pathways, are effective biotechnological strategies for fostering the release of HT from its conjugated forms. These approaches offer great potential for the sustainable recovery of HT from OMWW, contributing to the valorization of this environmentally impactful agro-industrial by-product. Processed OMWW can lead to clean-label HT-enriched foods and beverages, capitalizing on by-product valorization and improving food safety and quality. In this review, the most important aspects of the chemistry, technology, and microbiology of OMWW were explored in depth. Recent trends and findings in terms of both enzymatic and microbial bioconversion processes are critically discussed, including spontaneous and driven fermentation, using selected microbial strains. These approaches are presented as economically viable options for obtaining HT-enriched OMWW for applications in the food and nutraceutical sectors. The selected topics aim to provide the reader with a solid background while inspiring and facilitating future research and innovation.

The increased consumption of ready-to-eat fruits highlights the need for better control of microbial growth during their shelf life. Among bacteria, Staphylococcus aureus and Bacillus cereus are proposed as target species for testing alternative preservative methods. This study aimed to evaluate the antimicrobial effect of the cell-free supernatant (CFS) from LAB strains previously isolated from ready-to-eat fruits, used as a mixed solution, against both reference and native S. aureus and B. cereus, which were isolated from commercial ready-to-eat fruits. A specific challenge test was conducted on minimally processed orange slices, assessing the effect of CFS on the intentionally inoculated target bacteria using a culturing and quantitative PCR (qPCR) approach. Microbiological counts varied widely among samples, indicating an initial microbiota below legislative limits, mainly comprising total mesophilic and psychrophilic bacteria, which increased significantly after 8 days of storage. Additionally, our results demonstrated the food matrix’s capacity to support the growth of both target species, with the tested CFS mainly effective in reducing the growth of reference strains. The results of the physicochemical analyses showed that during refrigerated storage, the orange slices underwent changes in pH, color, and texture, mostly in S. aureus strain-inoculated samples, negatively affecting texture at mid-storage time. The study also underscored the importance of combining plate counting with qPCR methods to detect B. cereus, as it can be risky even at low levels.