Effect of air-drying temperature on physico-chemical, powder properties and sorption characteristics of pumpkin powders

This study examined the use of hot-air drying in the preparation of pumpkin powder. The drying temperature was varied (50, 60 and 70°C) to determine the effect of temperature on physico-chemical properties, powder properties and sorption characteristics of pumpkin powders. The results showed that a drying temperature of 70°C removes moisture from pumpkin slices faster than the lower drying temperatures of 50 and 60°C. The moisture content and water activity values of the pumpkin powder dried at 60 and 70°C were within acceptable limits for safe storage. Pumpkin powder dried at 70°C exhibited the darkest yellow color, while pumpkin powders dried at 50 and 60°C were lighter. Moreover, pumpkin powder dried at 70°C showed the highest percent decrease in carotenoid content (56%) compared to those dried at 50 and 60°C (18% and 33%, respectively). The results also showed that increases in drying temperature are accompanied by decreases in the water solubility, water and oil adsorption capacities of the resulting pumpkin powders. Pumpkin powders dried at 50 and 60°C had water solubilities of more than 50% and higher water adsorption and oil adsorption capacities than those dried temperature at 70°C. Overall, a good quality pumpkin powder can be produced by hot-air drying at a temperature of 60°C in terms of moisture content, water activity, color characteristics, total carotenoid content, bulk density, water solubility, water adsorption, and oil adsorption capacities. When drying at a temperature of 50°C, the moisture content and water activity of pumpkin powder was higher than the acceptable limit of that standard and the dark yellow color of the powder was observed when subjected at a drying temperature of 70°C. Working sorption isotherms of dried pumpkin powder were found to be Type II of all the sorption curves.