The effect of shrinkage during drying of potato spheres and the effect of drying temperature on vitamin C retention

Shrinkage data determined for drying potato spheres was compared to three models relating shrinkage to moisture content. Best results were obtained using a simple linear model. Drying of potato spheres was found to be almost ideally three dimensional and drying rate curves were found to contain two distinct falling rate periods. Having related shrinkage to moisture content and thus time, a drying curve was predicted using the Fickian model incorporating a Fourier number (accounting for shrinkage). A drying rate curve was also generated using a constant diffusion coefficient (assuming no shrinkage). Both models were found to describe the Ist falling rate period accurately, while the model accounting for shrinkage best described the 2nd falling rate period. Vitamin C was found to degrade exponentially during drying. An empirical equation was developed which described vitamin C degradation well over the temperature range 30-60 degrees C.