Influence of Steaming Times on Drying Time and Color Quality of Japanese Pumpkin ‎Powder from Step-Down Hot Air Drying Technique

The objective of this research was to study influences of steaming time and drying condition on drying time and color quality of Japanese pumpkin powder obtained from a step-down hot air (HA) drying. The experiments were conducted using Japanese pumpkin slices with a thickness of 1 mm, steaming for 0-1 min at atmospheric pressure,‎ and dried by hot air using a step-down hot air technique (60-90 C) until the final moisture content was reduced to 4% dry basis compared with no steaming condition.  The results indicated that steaming time was not affected the drying time of Japanese pumpkin slices, but the experimental condition affected the drying time. All cases of step-down HA drying were a shorter drying time than a HA drying at 60 C.‎  However, an increase in steaming time increases lightness (L) and yellowness (+b) of Japanese pumpkin powder, and also decrease the formation of white powder stains on the surface of the dried product.‎  The optimal condition for producing the Japanese pumpkin powder is a steaming for 1 min, and dried by a step-down hot air drying technique at of 90‎ C for 1 hr followed by 80‎ C for 1 hr followed by 70 C for 1‎‎ hr and followed by 65‎ C