Abstract:
This study was conducted to investigate the combined effect of solar tunnel dryer zones and
layer thicknesses on the drying characteristics, quality and safety of washed Arabica
parchment coffee. The experimental design was 4 x 3 factorial arrangements in a randomized
complete block design with three replications. The first factor was solar tunnel drier zones
(zone 1, zone 2, zone 3 and open sun drying) and the second factor was a layer of drying
thicknesses (2, 4 and 6 cm). Parameters such as moisture ratio, effective diffusivity, hours to
drying, were collected to determine drying characteristics of parchment coffee. Then
physicochemical quality parameters such as titratable acidity, total soluble solid, PH, Crude
fat, total polyphenol contents, total Antioxidant capacity, IC50, raw and cup quality) and
fungal load were determined. During the drying, drying air temperature and relative humidity
were measured continuously at one-hour interval. Moisture ratio was examined by moisture
loss at a given time per initial moisture content at every one hour interval. Selected 7 different
thin-layer drying models were compared to determine drying kinetics. According to statistical
analysis results, the Modified Midilli model has shown a better fit to the experimental drying
data as compared to other models. The effective diffusivity varied between (1.2 to 5.0*10-6
)
and increased with increasing temperature along the drying zones. All collected parameters
except TA differed significantly (p<0.05) concerning drying zones and layer thicknesses.
There was no significant variation among the treatments concerning cup quality and all the
coffee scored grade one and grade two for the total quality score referring to very good
quality for all the coffees. Higher fungal fungal were found for the sun-dried coffee beans
with aspergillus genera being the most abundant. The study concluded that drying parchment
coffee under zone 2 (solar tunnel drier 50-60 0
C and 18-28% RH) at a drying depth of 4 cm
resulted in desirable effects. Consequently, in the absence of a mechanical drier due to the
unavailability of its basic materials, the solar tunnel drier could be a worthy substitute
without compromising on coffee bean and cup qualities as compared to traditional open sun
drying
