Drying kinetics and physicochemical and technological properties of pumpkin puree flour dried by convective and foam-mat drying

The drying of pumpkin puree by convective (C) and foam-mat (FM) was investigated (45/65 degrees C). The FM drying provides 50% higher drying rates than convective at the same temperature. Both drying beds were porous. The FM bed was thinner than the convective, and structures associated with bubbles collapsing in the drying process were observed in its surface. All flours showed hygroscopic behavior, and high water-holding capacity (6.9-7.7 g water g/dw), but a lower monolayer water content was observed in foam-dried samples (0.04-0.06 g water g/dw). The FM drying at 45 degrees C produced flours with equivalent carotenoids content (855 mu g beta-carotene g/dw(1); p <= .05) than fresh puree, which may be associated with shorter drying periods observed. The flours progressive rehydration (25/40 degrees C) produced puree with the same firmness and adhesiveness as fresh puree. This result reveals the potential of foam-bed drying to make pumpkin flours, adding value to this raw material. Novelty impact statement For the first time, the foam-mat drying of "Tetsukabuto" pumpkin puree was studied and this method, at the same temperature, provides around 50% faster drying rates than the conventional hot-air drying. Although, the study is innovative using scanning electron microscopy (SEM) to register the foamed and nonfoamed dried bed, sharing differences in these bed morphologies. The foam-mat drying preserved the carotenoid content in dried puree, the flour presented high water-holding capacity and higher solubility index, and the rehydrated flour has the same firmness and adhesiveness as a fresh puree.