Orchard-Based Variations in Oil Content, Fatty Acid Composition, and Bioactive Compounds in ‘Tombul’ and ‘Palaz’ Hazelnut (Corylus avellana L.) Cultivars

Hazelnuts, which have high nutritional value, are an important source of fat, fatty acids, phenolics, and antioxidants. In this study, variations in the oil and protein contents, fatty acid compositions, and bioactive compounds of organic hazelnuts ('Tombul' and 'Palaz' cvs.) grown in seven different organic certified hazelnut orchards established with the ocak (multi-stemmed bush) planting system in Samsun (Türkiye) were evaluated. Except for protein, oleic acid, and linolenic acid, orchard-based variation in other traits investigated was significant. The effect of orchards on these traits varied depending on the cultivar. According to orchards, the oil content in the 'Tombul' cultivar varied between 61.1 and 64.4%, protein content between 14.3 and 15.3%, oleic acid content between 82.09 and 82.98%, linoleic acid between 7.49 and 8.44%, total phenolics between 5.51 and 15.92 mg g−1, total flavonoids between 4.86 and 23.20 mg 100 g−1, and antioxidant activity between 10.33–36.98 mmol kg−1 and 4.74–28.62 mmol kg−1 (according to FRAP and DPPH assays, respectively). 'Palaz' cultivar had a range of 59.41–62.92% for oil content, 13.22–15.51% for protein content, 82.05–83.15% for oleic acid content, 6.66–7.89% for linoleic acid, 4.65–9.15 mg g−1 for total phenolics, 4.45–7.56 mg 100 g−1 for the total flavonoids, and 9.17–23.58 mmol kg−1 and 3.54–15.50 mmol kg−1 for antioxidant activity (according to FRAP and DPPH assays, respectively). Principal component analysis (PCA) revealed that orchards in both cultivars were clustered at different points on the PCA plane and were associated with different traits. The findings showed that orchard-based variations in protein, oil, fatty acid compositions, and bioactive compounds in hazelnuts are significant.