Drying equipment: A programmable oven with 400 W (Drying
Oven Model SMA-112, Japan) was used. The drying oven is
equipped with a temperature control function that allows the user
to select the required drying temperature and also to adjust the
time of processing. The hot-air drying experiments were
performed using a drying tray (52 cm x 41 cm). Air was circulated
from above and the bottom of the perforated drying tray.
Drying procedure: Fresh kaffir lime (Citrus hystrix) leaf samples
with different loading capacities (0.5-2.0 kg/m2) were dried in a
drying oven (Smoke Master Model SMA-112, Japan) under
different drying temperatures (40-80°C) and drying time (3-15 h)
and prepared for optimization procedure based on a central
composite design (CCD) (Table 1). The term of loading capacity
can be defined as a specified amount of weight per square foot that is allowed to be placed on a given platform (tray). Drying
procedures were carried out as reported by Juhari et al. 48. During
drying process, samples were turned over every 1 hour for evenly
distribution of heat among samples. The oven was switched on 1
hour before the drying process to equilibrate the temperature.