Additionally, the change in physical stability of g-oryzanolloaded SLN was evaluated through the particle size and zeta potential measurements (Table 4). The results showed that the change in particle diameter of both concentrations at each storage temperature did not correlate with each other. Likewise, a small reduction in zeta potential of both investigated systems was found with storage time and temperature. However, the measured zeta potentials were still in the range from 40 to 59 mV in which these absolute values were higher than 30 mV for colloidal formulation, suggesting that particles were likely to be electrocchemically stable (Mehnert and Ma¨der, 2001; Souto et al., 2005; Souto and Mu¨ller, 2005).