The first fact observed in Fig. 1 is that the drying rate curves were overlapped. This confirms the reproducibility of the drying experiments. In Fig. 1, a typical drying rate curve can be observed. At first, the constant rate period can be observed from Y = 1.0 to Y ≈ 0.55, where, about 0.45 gH2O gds−1 min−1 were removed from the papaya seeds and, the water surface evaporation was the controlling mechanism. This drying period can be mainly attributed to the high initial moisture content of the papaya seeds. After, the falling rate period can be visualized from Y = 0.55 to Y ≈ 0.0. In this period, the internal diffusion cannot be more supply the water surface evaporation. As consequence,the temperature increased in the papaya seeds surface and, the drying was controlled by the internal diffussion mechanism. When the drying rate tends to zero, the falling rate finished and the equilibrium moisture content of the
papaya seeds was attained. Similar drying rate curves were found by Batista et al. (2007) in thin layer drying of chitosan with high initial moisture content.