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

## TL;DR

This study examines how overripe papaya slices shrink unevenly during drying at different temperatures and highlights the importance of considering shrinkage in drying models.

## Contribution

The study reveals anisotropic shrinkage in papaya slices during convective drying and shows the impact of shrinkage on moisture diffusivity modeling.

## Key findings

- Papaya slices showed significant height shrinkage (76-87%) compared to area shrinkage (15-26%) during drying.
- Ignoring height shrinkage led to overestimated moisture diffusivity, especially at higher temperatures.
- Drying at 60 °C resulted in near-ideal shrinkage with minimal deviation from linearity between water loss and volume reduction.

## Abstract

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.