Physicochemical and sensory properties of milk supplemented with dispersible nanopowdered oyster shell during storage

The current study was carried out to investigate the dispersibility of powdered oyster shell (POS), nanopowdered oyster shell (NPOS), and Zn-activated nanopowdered oyster shell (Zn-NPOS) in milk and to determine effects of adding oyster shell on the physicochemical and sensory properties of milk during storage at 4 degrees C for 16 d. To ensure dispersibility, 10% (wt/vol) oyster shell was added to distilled water and stirred at 800 rpm for 2 h, and then the emulsifier 0.5% polyglycerol monostearate (PGMS) was added and stirred continually for 24 h. The particle sizes of POS, NPOS, and Zn-NPOS were 180 mu m, 389 nm, and 257 urn, respectively. The pH values of all milk samples ranged from 6.62 to 6.88 during storage, and the zeta-potential of milks with NPOS and Zn-NPOS added were more stable than that of milk with POS in low concentrations (0.5 and 1.0%, vol/vol) during storage. The L and a color values of the milks were not significantly influenced by treatment; however, the b value (yellow-blue color) significantly increased during storage after adding POS, NPOS, or Zn-NPOS. Sensory analysis revealed that sedimentation score significantly increased with POS-supplemented milk, but the NPOS- and Zn-NPOS-supplemented milks did not show sedimentation until after 8 d of storage. Based on the data obtained, we conclude that dispersible nanosized oyster shell at concentrations of 0.5 and 1.0% (vol/vol) could be supplemented to milk without significant adverse effects on physicochemical and sensory properties.