Effect of superfine grinding on physicochemical and antioxidant properties of pomegranate peel

Pomegranate peel powders were prepared by superfine grinding, whose effects were investigated on the composition, functional and antioxidant properties of the pomegranate peel products. Fluidised bed jet milling technology was used to process superfine pomegranate peel powder. The physical-chemical properties of coarse powder A (D50 = 413.4 mu m) and B (D50 = 197.1 mu m), fine powder C (D50 = 142.6 mu m) and D (D50 = 41.2 mu m), superfine powder E (D50 = 7.68 mu m) and raw material powder (RMP) (D50 = 352.2 mu m) were investigated in this study. SEM images revealed the shape and surface morphology of six pomegranate peel powders. The physical determinations showed that the smaller the powder particle size was, the greater the surface area (from 0.214 to 1.597 m(2) g(-1)) and bulk density (from 0.653 to 0.751 g mL(-1)) were, the smaller the angles of repose (from 51.69 degrees to 38.74 degrees) and slide (from 48.32 degrees to 34.18 degrees) were. The water holding capacity (WHC), water-solubility index (WSI), polyphenols and flavonoids release were significantly improved as the size of pomegranate peel particle decreased. The results of FTIR and UV indicated that grinding process would not influence chemical composition of pomegranate peel. Vitamin C (VC) and butylated hydroxytoluene (BHT) were used in DPPH scavenging activity determination, and DPPH scavenging activity was A < RMP < BHT < B < C < D < E < VC.