Carbonyl trapping and antiglycative activities of olive oil mill wastewater

The use of natural compounds as antiglycative agents to reduce the load of advanced glycation end products from diet is very promising. Olive mill wastewater is a by-product of the olive oil extraction processes with a high content of hydroxytyrosol, hydroxytyrosol derivatives and molecules containing o-dihydroxyl functions such as verbascoside. Two powders were obtained after the ultrafiltration and nanofiltration of olive mill wastewater, and successive spray drying with maltodextrin and acacia fiber. The samples were characterized by phenolic composition and antioxidant capacity. Antiglycative capacity was evaluated by in vitro BSA-glucose and BSA-methylglyoxal assays, formation of Amadori products and direct trapping of reactive dicarbonyls (methylglyoxal and glyoxal). Both ultrafiltered and nanofiltered olive mill wastewater powders had an activity comparable to quercetin and hydroxytyrosol against the inhibition of protein glycation (IC50 = 0.3 mg mL(-1)). The antiglycative activity of the powder was further investigated after separation by reverse phase solid extraction. Fractions extracted with the methanol content higher than 40% and rich in hydroxytyrosol and verbascoside exerted the highest reactivity against dicarbonyls. Data confirmed that the direct trapping of dicarbonyl compounds is the main route explaining the antiglycative action rather than of the already known antioxidant capacity. Results support further investigations to evaluate the technological feasibility to use olive mill wastewater powders as antiglycative ingredients in foods or in pharmacological preparations in future.