Effects of hazelnut skin extract on the stability of hazelnut oil oleogels

In this study, the effects of hazelnut husk extract (HHE) on the oxidative stability, physicochemical properties, and rheological behavior of hazelnut oil-based oleogels structured with glyceryl monostearate (GMS) were investigated. The oleogels were prepared in the form of a control group, a sample containing synthetic antioxidant (BHA), and formulations with added hazelnut husk extract at different concentrations (0.20%, 0.40%, and 0.60 %). The samples were stored for 30 days and evaluated at specific intervals for acidity, peroxide value, TBARS, Rancimat induction time, color parameters, oil and water holding capacity, rheological properties, and FTIR analyzes. During the storage period, an increase in oxidative parameters was observed in all samples; however, in oleogels containing hazelnut husk extract, this increase was more limited compared to the control sample. Especially in oleogels containing 0.60 % extract, peroxide and TBARS values were found to be lower compared to the control group, while the Rancimat induction time was determined to be approximately 20-30% higher. The oil retention capacity increased with the addition of the extract, and in samples containing 0.60 % extract, an improvement of approximately 10-15% was observed compared to the control group. FTIR analyzes have shown that band changes in the fingerprint and aromatic regions indicate the integration of extract components with the oleogel matrix thru physical interactions. Rheological analyzes have revealed that all oleogel samples exhibited a decrease in viscosity with increasing shear rate and displayed pseudoplastic flow behavior. At low shear rates, viscosity values were measured in the range of 10³–10⁴ Pa·s, and the addition of the extract, particularly at concentrations of 0.40% and 0.60 %, significantly increased viscosity, indicating that the oleogel network structure was strengthened. In conclusion, it has been determined that hazelnut husk extract possesses significant potential as a natural and functional component that can enhance oxidative and rheological stability in hazelnut oil oleogels. Key Words: Antioxidant, Hazelnut skin extract, Oleogel, Oxidative stability