Using Olive Leaves to Enrich Olive Oil With Oleuropein Aglycone

Oleuropein is present in olive fruit and is converted during olive-oil manufacture into oleuropein aglycone, other downstream secoiridoid derivatives, and phenolic alcohols. Oleuropein aglycone is among the major phenolic constituents of extra virgin olive oil; however, concentrations of these compounds can vary substantially between batches of oil. Olive leaves, an oleuropein-rich by-product of the olive industry, may provide a source of phenolic compounds for targeted olive-oil enrichment. This study investigated the prospect of extracting phenolic compounds, particularly oleuropein, from olive leaves into an aqueous extract followed by enzymatic hydrolysis to oleuropein aglycone and assessment of its transfer to an oil phase. The impact of parameters such as dryness of the leaves when making olive leaf aqueous extract and different sources of β-glucosidase (almond flour, almond meal, and almond milk) to hydrolyse oleuropein to the aglycone were investigated. Among the conditions tested, drying leaves at 70°C produced the highest oleuropein concentration in the extract, and almond milk as the source of enzyme was the best combination to achieve hydrolysis of oleuropein. However, the transfer of the oleuropein aglycone from the aqueous extract to the oil phase was inefficient under the conditions tested, indicating that multiple factors were limiting the mass transfer.