Hydroxytyrosol is a naturally occurring polyphenol with remarkable antioxidant activity. Its precursor oleuropein is present in olive fruits but also in all parts of the olive tree. While oleuropein has several known biological activities, the activity of hydroxytyrosol may be even greater. Therefore, obtaining as much as possible hydroxytyrosol, rather than oleuropein, from the plant is desirable.
The agricultural waste produced from annual pruning of olive trees is normally disposed of by burning. However, these leaves and small branches also contain oleuropein. Here there is an opportunity to extract a high-value product from what is generally thought to be a waste material.
Recently, researchers have attempted to develop and optimize just such a process. Enzymatic reactions were developed to convert the original oleuropein into the desired hydroxytyrosol. Enzymes with varied characteristics such as molecular size, isoelectric point, and hydrophobic domains, were tested.
With a two-step reaction strategy, first the glucosidic bond was broken, followed by hydrolysis of the aglycon. They found that the first step alone required 7 days, at low concentration, and the second step did not work as expected, but seemed to also require enzyme action. The outcome was only 5% transformation.
They also examined a one-step reaction scheme using a different type of enzyme, and this process allowed for a higher concentration and obtained 30% transformation in 12 days. This process was much more effective than the two-step strategy.
However, with only 30% transformation, it may be possible to further optimize the process to obtain even better yield of hydroxytyrosol. On the whole, using a waste material to create a valuable product is bound to be a worthwhile endeaver.
Garcia-Molina G, Peters E, Palmeri R, et al. Enzymatic synthesis of hydroxytyrosol from oleuropein for valorization of an agricultural waste. Bioengineered. 2024 Dec;15(1):2396647. PMID: 39235136