Phenolic compounds of olive mill wastewater (OMW) samples from Spain and evaluation of their antioxidant potential

Aim: Industrial processes for olive production generate a considerable amount of oil wastewater, also known as "olive mill wastewater" (OMW), or alpechin, which is a great source of phenolic compounds. The aims of this study are to optimise the conventional extraction of the phenolic fractions present in the alpechín, to characterise the total phenolic content, and to determinate their antioxidant potential using the TEAC assay.

Method: To carry out the study, eight samples of olive mill wastewater (OMW) and five samples of alpechín sludge from abandoned ponds in the Mediterranean area and southern Spain were analysed. After sample defatting using hexane and subsequent drying in an oven, the total phenolic content and antioxidant properties of the extracts were analysed using spectrophotometric techniques.

Results: The samples of alpechín from Cordoba, Tarragona, Alicante, and Toledo, corresponding to codes TED-4, TED-15, TED-14, and TED-16, respectively, showed high TPC contents ranging from 7.2 g GAE/kg to 18.9 g GAE/kg. They also exhibited an antioxidant capacity equivalent to 10-60 micromoles of Trolox/g, significantly exceeding samples from other geographical locations. The polyphenol content of the alpechín samples was influenced by factors such as the matrix condition, seasonality, location, degree of abandonment of the ponds, and vegetation water. In addition, the pH, temperature, extraction technique, and solvent type also affected the recovery of phenolic compounds.

Conclusion: This study provides a solid basis for the implementation of innovative strategies for the valorization of this residual material as potential bioactive compounds for the food and agricultural industries.

Acknowledgements:

This research is part of the projects TED2021-129481B-C31 and TED2021-129481B-C33, funded by MCIN/AEI/10.13039/501100011033 and by the European Union “NextGenerationEU”/PRTR. Sergio Martínez-Terol would like to acknowledge TED2021-129481B-C33 for his contract.