Effect of microwave vacuum drying and hot air drying on the physicochemical properties of durian flour

Unripe durian cv. Monthong was subjected to microwave vacuum drying (MVD) at 1200, 1600 and 2200 W and hot air drying (HAD) at 40, 50 and 60 °C to produce durian flour. Drying rate of MVD and HAD was 0.34–0.58 kg water kg dry solid−1 min−1 and 0.02–0.06 kg water kg dry solid−1 min−1, respectively. An increase in drying rate by either increasing hot air temperature or increasing microwave power decreased the degree of crystallinity from 21.95% to 2.31% and from 7.72% to 4.05%, respectively. Moreover, the increased drying rate caused a decrease in endothermic enthalpy (ΔHgel) and pasting properties. Starch content of the durian flour was 41.40–47.03%. The starch granule morphology of durian flour was disrupted which indicated gelatinisation of flour during drying. Due to a short drying process, the MVD flour had less a*-value (P ≤ 0.05) than the HAD flour.