Optimization of vacuum drying conditions for a steamed (pumpkin-) sweet potato slab by response surface methodology

Vacuum drying was conducted for a steamed pumpkin-sweet potato slab to improve its quality, convenience and preference as snack. Steamed sweet potato was dried from 30 to 60°C for 12 hr, after which moisture contents, colors, and taste were evaluated. The lowest moisture content was 0.22% upon vacuum drying at 60°C for 12 hr. Lightness decreased while other color values (a, b and ΔE) increased with increasing drying temperature and drying time. Reducing sugar and soluble solid contents ranged from 98.7~268.11 mg/g and 19~72°Brix, respectively. Sensory score of the sample was the highest when dried at 50°C for 6 hr. The optimum drying conditions were predicted to be 48.5~62°C and 5.1~7.1 hr by response surface methodology.