Anisotropic Shrinkage Behavior of Overripe Papaya Slices (Carica papaya L. cv. Sunrise) during Convective Drying

This study investigated the shrinkage behavior of overripe papaya slices during convective drying at 50 and 60 °C under 20% relative humidity, without disturbing the process. The Lewis model accurately described drying kinetics at both temperatures. Papaya slices exhibited anisotropic shrinkage, with area and height reductions of (15 ± 3) % and (76 ± 5) % at 50 °C and (26 ± 7) % and (87 ± 3) % at 60 °C, respectively. Although fundamental models were evaluated, only empirical correlations effectively described area and height shrinkage at both temperatures. At 50 °C, a deviation of approximately 10% from linearity was observed between water loss and sample volume reduction, while at 60 °C, a deviation below 5% occurred, suggesting an ideal shrinkage. These differences could be related to the gap between the sample and glass transition temperatures. Drying rate behavior was comparable at both temperatures, despite the occurrence of area shrinkage, which could be explained by the relatively small extent of area shrinkage. At 50 °C, no constant period was observed, followed by a single falling rate period, whereas at 60 °C, a short constant rate period was followed by two falling rate periods. Effective moisture diffusivity was evaluated with and without considering height shrinkage. When height shrinkage was neglected, diffusivity values were overestimated, particularly during the second falling period at 60 °C, when moisture mobility is expected to decrease. These findings highlight the importance of incorporating shrinkage into drying kinetics modeling.