Antioxidant activity, and phenolic and mineral contents of the walnut kernel ( <i>Juglans regia</i> L.) as a function of the pellicle color

Introduction. The objective of this study was to investigate some nutritional and functional components of the walnut fruit kernel and pellicle across twelve genotypes of Juglans regia L., six with a red pellicle and six with a light yellow pellicle. Materials and methods. Antioxidant activity, and contents of total phenolics, flavonoids, minerals and trace elements were determined as well as anthocyanins in red pellicles. Results and discussion. Total phenolic content ranged from 1,131 to 2,892 mg GAE 100 g-1 in kernels and from 11,525 to 33,833 mg GAE 100 g-1 in pellicles. The ratio between the average content in pellicles and that in kernels was found to be 12.7 for total phenolics and 12.9 for the antioxidant activity. Significantly higher average levels of total phenolic content and flavonoid content were found in yellow pellicles than in red pellicles, while no significant differences between the two groups of genotypes were found in kernels. High concentrations of anthocyanins were found in the red pellicles (1,636–2,956 mg CGE 100 g-1 ). The contents of calcium, magnesium, iron and manganese were significantly higher in genotypes with a red pellicle compared with genotypes with a yellow pellicle both in kernels and pellicles, while the opposite is true for potassium and sodium. Conclusion. The data confirm that walnuts are a good dietary source of total phenolics with high antioxidant potential, minerals (Ca, Mg and K) and essential elements (Fe, Mn, Cu and Zn), most of which are concentrated in the walnut pellicle. Despite the large amounts of anthocyanins found in the red pellicles, yellow pellicles had a stronger antioxidant activity than red pellicles.

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