In other words, the AN molecule in the AN/KF sample is sterically protected from atmospheric oxygen by the intercalation to the inter layer space of KF. The enhancement of the durability against alkaline environment may also be considered due to the steric hindrance from the attack of hydroxyl ion to the anthocyanin dye. Similar steric hindrance effect, together with the electrostatic effect, has been proposed about the stability enhancement by the copigmentation in natural anthocyanin (Dyrby et al., 2001; Mazza and Brouillard, 1987).