Effects of Tannins on the Stability of Sterols in Food Emulsions

The oxidation of sterols, including phytosterols and cholesterol, poses significant challenges for food science and human health. Effective stabilization strategies are crucial, especially in emulsified food systems, where sterols are prone to oxidation due to their localization at the interface. Natural antioxidants, such as tannins, have gained attention for their antioxidant properties and their ability to bind sterols. This Ph.D. project aims to investigate the antioxidant and binding properties of two types of tannins - chestnut tannins and quebracho tannins - in O/W emulsions. The study will focus on assessing their impact on lipid and sterol oxidation. Furthermore, it will investigate how the interaction between tannins and sterols influences their oxidative stability. Both tannins (chestnut and quebracho) showed strong antioxidant effects when added to emulsions. However, when sunflower oil was used as the lipid phase, quebracho tannin resulted in lower peroxide and hexanal values. In contrast, when egg yolk lipid fraction was used, chestnut tannin displayed a stronger effect, suggesting a potential synergistic interaction with the carotenoids naturally present in egg yolk. Interaction analysis revealed that when sterols (cholesterol, β-sitosterol, campesterol, and stigmasterol) were combined with quebracho tannin, DSC indicated amorphization of the system compared to individual components. This was confirmed by SEM images, which showed a change in the crystalline structure of the sterols. Additionally, the aqueous phase of emulsions containing tannins exhibited increased concentrations of cholesterol and β-sitosterol, suggesting a change in sterol solubility when bound to tannins. This study provides the first evidence that tannins can act as both primary and secondary antioxidant agents. Moreover, the interaction between tannins and sterols opens multiple pathways for the formulation of innovative, fortified food products.