Toward Functional Oil Blends: Physicochemical and Nutritional Evaluation of Rapeseed–Hazelnut Oil Mixtures

The combination of rapeseed oil (RO) and hazelnut oil (HO) was selected to create a functional blend integrating two technologically complementary lipid matrices. RO is valued for its favorable fatty acid (FA) profile, particularly its low saturated FA content and the presence of essential polyunsaturated FAs, whereas HO is characterized by high monounsaturated FA levels and inherently greater resistance to oxidative deterioration. Blending these oils enables the formulation of mixtures that balance nutritional quality with improved physicochemical stability, without the need for chemical modification. Such an approach is relevant for applications requiring oils that retain desirable characteristics during storage and handling. In this context, the present study aimed to evaluate the quality characteristics, FA composition, triacylglycerol (TAG) structures, and oxidative stability of binary blends of RO and HO. Two commercial oils, as well as their blends in RO:HO volume ratios of 3:1, 1:1, and 1:3, were tested. The samples were stored under two temperature conditions: 4 °C (refrigeration) and 20 °C (room temperature), and analyzed after two and four months of storage. Initial MUFA content ranged from approx. 61-74%, increasing with HO proportion, whereas PUFA levels decreased accordingly (from ~28% in RO to ~10% in HO-rich blends). The <i>sn</i>-2 TAG position was predominantly occupied by unsaturated FAs (>80%). Statistical analysis (<i>p</i> < 0.05) showed that both storage time and temperature significantly affected PV, while no significant differences were observed in the overall proportions of SFA, MUFA, and PUFA. Blends with a higher proportion of RO exhibited increased AVs, suggesting greater susceptibility to hydrolytic changes, whereas mixtures enriched in HO demonstrated superior oxidative stability, as reflected by significantly lower peroxide values (<i>p</i> < 0.05), which can be attributed to their lower PUFA content. The 1RO:3HO blend exhibited the most favorable balance between beneficial nutritional indices and stability against quality deterioration over the storage period. The results indicated that the formulation of balanced mixtures combining the favorable FA profile of RO with the oxidative resistance of HO represents a promising approach for obtaining oils with improved functional and nutritional properties.