Optimization of ultrasound-assisted grape vinegar fortified with olive leaf powder: effects on bioactive and functional properties

In this study, functional grape vinegar enriched with olive leaf powder was produced and subsequently subjected to ultrasound treatment. Response Surface Methodology (RSM) was used to optimize the ultrasound treatment conditions; amplitude, treatment time, and olive leaf powder concentration were evaluated as independent variables. Total phenolic content (TPC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity were considered as response variables. Optimum conditions were determined to be 80% amplitude, 4 min treatment time, and 0.6848% olive leaf powder. Under these conditions, the experimental TPC and DPPH values were determined to be 91.68 mg GAE/100 mL and 70.95%, respectively. Furthermore, the effects of different treatments on the total flavonoid content, color characteristics, and antimicrobial activity of the grape vinegar were also investigated. The results showed that the GV-US+OLP sample was superior to both the control and thermal pasteurization groups in total phenolic and flavonoid content, as well as in antioxidant activity. While limited changes were observed in color parameters, the total color change was lower in the ultrasound-treated and enriched sample. Antimicrobial analysis revealed that only the ultrasound-treated grape vinegar fortified with olive leaf powder (GV-US+OLP) sample exhibited inhibitory activity, particularly against Escherichia coli. Overall, the findings indicate that combining ultrasound with olive leaf powder is an effective approach for improving the functional and microbiological quality of grape vinegar.