The puffing operation is carried out at as intermediate stage in the drying process. When reconstituted, the dehydrated puffed product presents a more pleasing appearance than the material that has not been puffed. The high temperature and short time process (HTST) was employed to obtain puffed sweet potato slices from both in natura and osmotically pretreated with sucrose and salt solutions samples. Processing time was the most significant variable affecting moisture content, water activity and rehydration. All the empirical models obtained using response surface methodology were considered predictive. The best conditions for the HTST sweet potato slices were obtained using a temperature of 160 degrees C and time of 22 min for samples with no osmotic treatment and a temperature of 150 degrees C and time of 10 min for samples submitted to the osmotic treatment. Scanning electronic microscopy confirmed the formation of pores within the tissue, and surface sealing during the HTST process as the samples puffed up (volume increase). The shortest convective drying time corresponded to the sample treated only by the HTST process. (C) 2007 Elsevier Ltd. All rights reserved.