Akademik Veri Yönetim Sistemi
European Journal of Lipid Science and Technology, 2025 (SCI-Expanded, Scopus)
Hazelnut oil extracted from hazelnut fruits is refined to enhance its edible properties. Bleaching is one of the key refining steps for high-acid oils such as hazelnut oil because they are generally subjected to physical refining. This study aimed to investigate the effects of earth type and deacidification on hazelnut oil quality during bleaching. For this purpose, degummed and deacidified hazelnut oils were subjected to bleaching using neutral and acid-activated clays at various ratios (1.25%, 2.50%, and 3.75%). Deacidification was achieved using a molecular distillation (MD) unit, and the free fatty acid (FFA) content of degummed hazelnut oil was reduced from 12.6% to 2.24%. The MD process also effectively decreased peroxide value (PV) and tocopherol content, which were also reduced by bleaching treatments. More tocopherol loss and peroxide decomposition were also observed with acid-activated clay during bleaching; the latter resulted in triene conjugation. Using acid-activated earth increased stigmastadiene formation by the removal of one molecule of water from the sterols. Besides, distilled oil lost more tocopherol after this process than non-distilled oil. Distillation did not affect color values, while bleaching earth and ratio considerably affected their reductions. Practical Applications: High-acid oils are generally refined with physical methods such as degumming, bleaching, and distillation to reduce refining loss. Pre-deacidification, performed by distillation, is applied to these oils before or after bleaching to reduce the free fatty acid content to less than 2%. This study examines the impact of the sequence of distillation and bleaching treatments, as well as the type of earth and ratio, on the quality of hazelnut oil. The findings indicated that the application of distillation before bleaching did not affect the color removal during bleaching; however, this method resulted in greater tocopherol losses compared to applying distillation after bleaching. Tocopherols are known to play a protective role against lipid oxidation, and therefore, their reduction is considered undesirable for maintaining oil quality.