Combined Drying Technologies for High-Quality Kiwifruit Powder Production

Freeze-drying is a dehydration technique which, from a sensory, nutritional and functional point of view, provides high-quality powder products. Nevertheless, both long processing times and high economic costs are required. In this study, pre-drying the samples using hot air or microwave has been considered in order to reduce the initial product's water content thereby shortening the freeze-drying time so as to obtain high value products at a reduced cost. The effect of dehydration pre-treatments on the kinetics, antioxidant activity and solubility of freeze-dried kiwifruit products was evaluated. Nine different thin-layer semi-theoretical models were used to fit the drying data. According to the obtained results, the pre-treated samples exhibited higher drying rates than the fresh sample. In turn, the dehydration pre-treatments used did not affect the solubility or the antioxidant activity of the samples.