Shrinkage, porosity and density behaviour during convective drying of spirulina

Spirulina (Arthrospira platensis) is a microalgae produced for its nutritional and therapeutic qualities. Drying is the main process of conservation used for this product and it is so essential to control its drying parameters. In this study, shrinkage, porosity and density of spirulina cylinders during convective drying were investigated. For 3, 4 and 6 mm diameter cylinders, results showed a weak and anisotropic shrinkage. The glass nature of the product during the drying process tended to reduce its shrinkage and to facilitate formation of pores and cracks. The product had a final porosity approaching 80% and most of its evaporated water during drying was replaced by gas. The apparent density strongly varied during drying. Its value decreased from 850 kg/m3 at the beginning of the drying to about 300 kg/m3 at the end of the drying. The effective water diffusivity was influenced by shrinkage. Its value was over-estimated about 36.48% to 92.41% when shrinkage was not considered in data processing.