Drying of foods using supercritical carbon dioxide — Investigations with carrot

The use of supercritical carbon dioxide (scCO2) for the removal of moisture from cylindrical pieces of carrot has been investigated. The experiments were carried out at 20 MPa pressure and the effects of temperature and co-solvent (ethanol) addition were examined. At the investigated conditions, comparisons with air-drying indicated that drying kinetics and the associated drying mechanisms differed between the techniques. The microstructural characteristics of carrot pieces that had been dried using the different techniques were compared using X-ray microtomography and light microscopy. Carrots dried in the supercritical fluid environment were seen to retain their shape much better than air-dried carrots which underwent shrinkage. Samples dried in ethanol-modified scCO2 possessed less dense structures and consequently displayed more favourable rehydrated textural properties than the air-dried equivalents.Industrial relevanceDrying is a common unit operation in food processing, but the rehydrated product is often of very poor quality. Comparatively little work has been done on optimising drying for quality of the final, rehydrated product. Supercritical drying is a possible way of maintaining product microstructure, and this paper describes experiments in which the supercritical drying of carrot is studied and compared with conventional processes.