Comparative analysis of phytochemical compounds and quality characteristics during the juvenile stage of hazelnut cultivars from Italy and Türkiye

The present study aimed to comparatively analyze phytochemical compounds and quality characteristics of hazelnut cultivars from Italy (‘Tonda Gentile Romana’, ‘Tonda di Giffoni’, ‘Nocchione’, and ‘Mortarella’) and Türkiye (‘Tombul’, ‘Foşa’, and ‘Çakıldak’), cultivated under identical ecological conditions. In this scope, a comprehensive evaluation of the physical characteristics of the nuts and kernels, biochemical properties (total phenolics, total flavonoids, antioxidant activity), protein, oil, ash contents, and fatty acid composition were conducted in cultivars. A wide variation was observed in the characteristics investigated among hazelnut cultivars. In the study, physical characteristics were determined as nut weight between 1.82 and 3.31 g, kernel weight between 0.96 and 1.49 g, shell thickness between 1.10 and 1.96 mm, and kernel percentage between 39.61 and 52.87%. The biochemical properties included total phenolics, total flavonoids, and antioxidant activity (according to DPPH and FRAP assays), which ranged from 21.84 to 50.86 g GAE kg− 1, 3.11 to 6.09 g QE kg− 1, 13.15 to 37.51 mmol TE kg− 1, and 57.22 to 102.13 mmol TE kg− 1, respectively. The oil content was found to vary from 52.46 to 65.74%. Also, palmitic acid (C16:0) varied between 4.66 and 5.79%, stearic acid (C18:0) varied between 1.71 and 2.76%, oleic acid (C18:1) varied between 83.21 and 87.37%, and linoleic acid (C18:2) varied between 4.25 and 8.77%. Principal component analysis indicated that the examined characteristics were highly effective in describing the variation among cultivars, with the first three principal components accounting for 84.9% of the overall variability. This comparative study demonstrates considerable variation in physical and biochemical characteristics among Italian and Turkish hazelnut cultivars. Results provide important information for future cultivar selection and breeding programs, highlighting characteristics desirable for specific commercial and industrial treatments.