Novel Hybrid Drying Methods, Preceded by Different Pretreatments, Used to Obtain Pumpkin (Cucurbita Maxima) Powder

This work presents the changes in the physico-chemical properties of pumpkin puree, aiming to find the best drying technique to obtain pumpkin powder. For that, pumpkin purees were pretreated by microwave (210 W and 315 W) for 3 min or ohmically heated at 17.5 V/cm for 2 min, followed by different drying methods: combined microwave (210 W and 315 W) and forced convection (100 °C) drying simultaneously. The samples of pumpkin puree (Cucurbita maxima) with 92.82 ± 0.1% moisture content, were dried until powder moisture reduced to 8.0 ± 0.3%. Drying time decreases with increased microwave power from 18 min up to 16 min for the samples pretreated by microwave and ohmic heating. A thermal pretreatment such as microwave or ohmic heating is an essential operation in the processing of fruits and vegetables. It not only contributes to the inactivation of polyphenoloxidase, peroxidase, but also could induce some changes in: carotenoids, polyphenols or antioxidant capacity. The results of qualitative analysis showed a product improvement due to ohmic heating pretreatment as compared to microwave technique. Free radical scavenging capacity for samples pretreated by microwave is lower (20.64–28.32% DPPH inhibition) compared to the ohmic heating (36–40.32% DPPH inhibition).