A Study about the Effects of Supercritical Carbon Dioxide Drying on Apple Pieces

Abstract

The work explores the feasibility of supercritical carbon dioxide (SC-CO2) as alternative drying food process. Experiments carried out with apple pieces at 10 MPa and 35°C, aimed to investigate the effect of the drying time (5÷120 min) and the addition of a pre-dehydration step in graded ethanol (EtOH) solutions on the dehydration of the final product in terms of weight loss and structure. The treatment with pure EtOH leaded to a weight reduction of 50.0 ± 0.2 % after 120 min while SC-CO2 induced a reduction down to 18.53±1.57 % after the same drying time. Significant improvements in terms of weight loss were obtained when apples were first dehydrated in pure EtOH for 40 min, and subsequently in SC-CO2 for 10 min reaching a final reduction of 11.67±2.55%. Color measurements indicated that both SC-CO2 and EtOH-SC-CO2 drying treatments induced a significant increase of L*, while an increase of a* and b* parameters was detected only for SC-CO2 dried apples. The overall changes in color ΔΕ did not shown significant differences between the two dried samples. SEM images indicated that the EtOH-SC-CO2 dried apples presented more shrinking and a wider pore distribution compared to the SC-CO2 dried ones. EtOH-SC-CO2 drying confirmed the potential to apply the technology for drying apple slices in short time.