Ultrasound-assisted vacuum drying of nectarine

Abstract

Convective drying is a widely used conservation process, and in an attempt to improve it, the use of ultrasound and/or vacuum can be an alternative. The objective of this work was to evaluate the influence of ultrasonic waves and vacuum, combined or not, on the drying kinetics at 60 °C and the impact in terms of fruit quality, through the following techniques: ultrasonic assisted drying (USD), vacuum drying (VD), ultrasonic assisted vacuum drying (USVD) and control drying (CD). Six different semi-theoretical drying mathematical models were compared based on their coefficient of determination and mean square error to characterize the drying curves. The application of the USVC technique resulted in a higher rate drying kinetics and a reduction of the process time above 50%. The dehydrated kinetics was successfully described by the Two-terms Exponential model. Effective moisture diffusivities were in the range of 10−9 m2/s and the higher value was obtained for USVD. It was verified that the use of ultrasound (USD and USVD) had a strong influence in obtaining the highest retention of polyphenols, while the use of vacuum (VD and USVD) resulted in lower color differences of processed samples in relation to fresh fruit and lower energy consumption. Thus, the combined use of ultrasound and vacuum can provide satisfactory results.