Characterization of walnut, almond, and pine nut shells regarding chemical composition and extract composition

• DOI: 10.1007/s13399-019-00424-2
• Publication Date: 2019-05-09T22:47:08Z
• Authors: Carla S. G. P. Qu...; Sofia Cardoso; Ana Lourenço; Joana Ferreira; Isabel Miranda; Maria José V. Lou...; Helena Pereira
• Keywords: 0106 biological sciences; 01 natural sciences; 0105 earth and related environmental sciences

The shells of three important food nuts, walnut, almond, and pine nut, were studied in view of valorization as residues. The shells differed chemically: walnut shells had 10.6% extractives, 30.1% lignin, and 49.7% polysaccharides; almond shells 5.7% extractives, 28.9% lignin, and 56.1% polysaccharides; and pine nut shells 4.5% extractives, 40.5% lignin, and 48.7% polysaccharides. The polysaccharide composition also differed, e.g., glucose/xylose ratio of 1.12, 0.94, and 2.29 for walnut, almond, and pine nut shells, respectively. Walnut and almond shells have a SG lignin (S/G 1.6 and 1.0, respectively) and pine nut shell a G lignin. The lipophilic extracts contained mostly saturated and unsaturated alkanoic acids. The ethanol-water extracts contained total phenolics, flavonoids, and condensed tannins. The antioxidant activity was moderate (IC50 15.2, 7.9, and 8.2 μg/mL for walnut, almond, and pine nut). The three nut shells fractured easily with little formation of fines.