Abstract |
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 mu g/mL for walnut, almond, and pine nut). The three nut shells fractured easily with little formation of fines. |