Abstract:

The effects of sample thickness, surface load, drying temperature, air velocity and evaporator bypass air ratio
(BAR) on the drying characteristics and quality of yacon during heat pump drying (HPD) were investigated. Experimental
results showed that higher thickness and surface load resulted in lower drying rate (DR). DR increased with increasing
drying temperature and air velocity. Most DR curves displayed both long time falling rate period and relatively short time
constant rate period while only falling rate period existed in some DR curves. Thickness of 2－4 mm, surface load of
1－2 kg/m2, drying temperature of 25－35 ℃ and air velocity of 1.5－2.0 m/s were preferred by considering specific
moisture evaporation rate (SMER), total color difference (ΔE), shrinkage ratio (SR) and rehydration ratio (RR). However,
BAR had little influence on the HPD process of yacon.

Key words: heat pump drying, yacon, drying characteristics, quality