Enhancing hydroxytyrosol stability via site-specific glucosylation

Hydroxytyrosol (HT), a phenolic compound found in olive fruit and oil, has notable biological activity; however, its susceptibility to oxidation limits its application. In plants, HT is naturally glycosylated but the functional relevance of this modification remains unclear. In this study, we investigated the effect of glycosylation positions on HT stability. We successfully synthesized and purified three HT glucoside (HTG) regioisomers using enzymes with position-selective glycosylation activity toward HT. The results revealed that the meta- and para-positions of HT, especially when the para-position is glucosylated, exhibit high stability even under conditions of enhanced catechol oxidation. Glucosylation at specific positions significantly influences the stability of HTGs. Furthermore, HTGs can be converted back to HT via acidic or enzymatic hydrolysis, highlighting its potential as a stable bioactive compound for food- and health-related applications. This study provides valuable insights into the stability mechanism of HTGs and its potential industrial application as a functional material.