Quality and Drying Characteristics of Apple Cubes Subjected to Combined Drying (FD Pre-Drying and HAD Finish-Drying)

Abstract

The drying methods tested were hot-air drying (HAD) and freeze-drying (FD), as well as a combination of blanching (100C, 1 min) prior to FD pre-drying and HAD finish drying. The effect of drying methods on moisture content, temperature, energy consumption, duration of drying, rehydration properties, color, texture and sensory were determined. Apple’s HAD and FD kinetics was described by an exponential and third-degree polynomial model, while the combined drying-blanching prior to freeze pre-drying and hot-air finish-drying (BFDHAD) kinetics consisted of two periods: polynomial until a converting point and exponential beyond that point. Among the products, the quality of apple samples processed by FD was the best, followed by BFD-HAD, whereas the products made using HAD were the worst. The drying times obtained for HAD and BFD-HAD were shorter than the drying times obtained for FD. The best BFD-HAD process, from quality and energy consumption considerations, was found to a moisture content of 30% w.b. (BFD time: 12 h), followed by 3 h of HAD. It was observed that BFD-HAD can reduce by about 8 h the time needed for FD.