Effect of Drying Method on the Quality of Sweet Potato Powder

The study was undertaken to evaluate the effect of different drying methods viz. drum drying, spray drying and tray drying on the quality of sweet potato flour/powder. Red skinned sweet potato was procured from local market and was subjected to pretreatments. Sweet potato roots were cut into small pieces, cooked in a steam cooker for 20 minutes and cooled to a room temperature. Cooked sweet potatoes were mashed in a mixture and mixed thoroughly and dried in double drum dryer. The sheets of dried sweet potato were collected, crushed and milled in a hammer mill and powder collected was tested for various parameters. In spray dryer, sample was rehydrated using distilled water and malto-dextrin was added to make the solid content about 20%. Samples of uniform size 5mm thickness were spread evenly in single layer on aluminum trays of tray drier and dried at a temperature of 65°C and at 1.5 m/s air velocity. The samples were weighed after every 30 minutes and drying was continued till the weight of samples was stabilized. After drying, sample was crushed into powder using a hammer mill. The quality of sweet potato flour/powder was evaluated using different quality parameters viz. color, moisture content, powder recovery and ash content. It was observed that powder prepared by spray drier had minimum change in quality parameters viz. moisture content (5%), ash content (5.12%), overall change in color (8.69) and the percentage recovery of powder per 100 g of sample was (20%), followed by the powder prepared by tray dryer moisture content (7%), ash content (5.73%), overall change in color (8.88) and percentage recovery of powder per 100 g of sample (30%). It was found that sweet potato powder prepared by spray drying method was good in quality as the powder formed was uniformly dried and had a uniform color and texture.