Influence of Microwave Drying Method on the Characterists of the Sweet Potato Dices

Three different drying methods, microwave spouted bed drying (MSBD), microwave-vacuum drying (MVD), and hot air drying (AD), were used to dry diced sweet potato. The drying characteristics and product quality are discussed in terms of the drying kinetics, rehydration ratio, expansion ratio, breaking force (crispness), product colour, and retention of β-Carotene. As expected the drying rates in MSBD and MVD were much faster than that obtained in hot air drying; the largest drying rate was obtained in MSBD with 2.5 W•g-1 MW power level. The products dried using MSBD and MVD displayed good puffing: rehydration ratios were about 2.0 after 18 min, expansion ratio was close to 1.0, and the breaking force below 600 g. The colour of MSBD product was uniform as well. Retention of β-Carotene was about 80 percent in MSBD and MVD but only 40 percent in AD product compared to that present in the fresh produce.