Effect of pulverization on the antioxidant activity of water caltrop (Trapa taiwanensis Nakai) pericarps

This study was to investigate the effect of pulverization treatment on the antioxidant properties of water caltrop pericarps. The results showed that crude fiber was the largest proportional constituent of water caltrop pericarps, comprising 72.3 g/100 g (dry basis). After 10 min milling, five fractions were obtained 1–5 different particle sizes (285, 211, 138, 62 and 41 μm, respectively). Comparing the effect of pulverization on the fiber component of each fraction, the fraction 1 exhibited higher hemi-cellulose but lower lignin than smaller particle size fraction except fraction 5. At a dosage of 250 μg/mL methanol extracts, the highest free radical-scavenging ability is obtained in the fraction 5, which is found to be 78.3 g/100 g, followed by the fractions 1–4. The same tendency was observed in the reducing power and cupric ions chelating ability. The fractions 1 and 5 contained significantly higher total phenolics and total flavonoids than fraction 2–4 (p < 0.05).