Drying constant during falling rate period (h-1) calculated by diffusion equation; k 1 : Drying constant during falling rate period (h-1) calculated by Lewis' equation; k 2 : Coefficient of browning rate (h-1); k': Coefficient of decomposition rate; L: Characteristic length (m); M: Moisture content (d.b. decimal); M e : Equilibrium moisture content (d.b. decimal); M exp,i : i th experimentally observed moisture content; M pre,i : i th predicted moisture content; m a : Measured value of ascorbic acid (mg• L-1