Mineral composition of two walnut cultivars originating in France and California

Mineral composition of two walnut cultivars (Franquette and Hartley) originating both in France and California was determined. Microwave assisted mineralisation was followed by atomic absorption spectrometry for all minerals except selenium which was quantified by gas chromatography–mass spectrometry (GC–MS), and phosphorus by a colorimetric method. Three elements presented major level differences linked to variety or origin. For origin, potassium levels of the French walnuts were higher (Franquette: 487 and Hartley: 466 mg 100 g−1) than those of the Californian walnuts (Franquette: 358 and Hartley: 372 mg 100 g−1). Inversely, sodium level was higher in the Californian Hartley than in the French Hartley (6.7 vs 0.3 mg 100 g−1). For variety, high levels of magnesium were observed for the Franquette cultivars (French: 191 and Californian: 202 mg 100 g−1) while the Hartley levels were lower (French: 129 and Californian: 134 mg 100 g−1). The same observation could be made for zinc, but the differences were weaker. Nevertheless, these data could not differentiate the walnuts according to origin or variety.