Characterization of virgin walnut oils and their residual cakes produced from different varieties

This study addresses the composition and properties of different walnut varieties (Chandler, Hartley and Lara), in particular their virgin oils and residual cakes obtained by screw pressing employing different cultivars. Among nuts, walnut (Juglans regia L.) exhibits interesting nutritional value, mainly due to their high content in linoleic acid, phenolic and tocopherol compounds, which show antioxidant and other healthy properties. Valuable results related to fatty acid profile and minor components were observed. Virgin walnut oil is a rich source in linoleic acid (60–62%) and γ-tocopherol (517–554 mg/kg). Moreover, walnuts show a very high content in total phenolic compounds (10,045–12,474 mg/kg; as gallic acid), which contribute to a great antioxidant activity (105–170 mmol/kg for DPPH, and 260–393 mmol/kg for ORAC), being the hydrolysable tannins (2132–4204 mg/kg) and flavanols (796–2433 mg/kg) their main phenolic groups. Aldehydes account for the highest contribution to aromatic volatiles in virgin walnut oil (about 35% of total). As expected, polar phenolic compounds concentrate in the residual cake, after the separation of the oily phase, reaching a content of up to 19,869 mg/kg, leading to potential added value and applications as source of bioactive compounds to this by-product.