2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
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temperature and relative humidity was about 12.8
q
C and
2.5% during the experimental time, respectively. This
explicitly indicates that the drying rate in the greenhouse
drying will be higher that open sun drying.
When designing for solar drying, information on the
temperature rise of air with solar radiation is important. If
the inlet temperature is close to ambient temperature, the
temperature rise varies almost linearly with incident
radiation [12]. The plot of average temperature rise is
shown in Fig. 6 along with the regression line for
temperature rise and the incident radiation. Equation for
predict the temperature rise is given as follows:
785 .4 001 .0
'
G T
(R
2
=0.81) (5)
Fig. 6. Variations of temperature rise in the greenhouse dryer.
The drying curves of pork in the greenhouse dryer and
open sun drying process are presented in Fig. 7. As
shown in Fig. 7, the initial moisture content of around
210% db was dried to the final moisture content of about
70% db in 280 min, while the open sun drying was about
340 min. Greenhouse dryer had a shorter drying time
compared to open sun drying. In other words, drying time
was reduced to about 21.4% by the greenhouse dryer
according to open sun drying.
Fig. 7. The moisture content of pork dried in the greenhouse dryer and
open sun drying.
Janjai et al. [5] reported that the drying efficiency of
the greenhouse dryer increase linearly with the loading
capacity, and this implies that the dryer should be
operated at the highest permissible efficiency. Therefore,
The 40 kg of pork (the highest load) was dried in the
greenhouse to obtain the highest drying efficiency. The
maximum and daily drying efficiencies of the greenhouse
dryer were 65.4% and 44.8%, respectively.
The values of hardness and shrinkage are presented in
Table 1. Hardness describes the texture of dried pork
after drying. It was found that the compression force to
penetrate the slice sample from all conditions is very low.
This is due to the texture still being soft as there is about
70% db. water remaining in the sample. This moisture
content level is not low enough for safe storage (water
activity is over 0.7). As, it is not the final product, it
needs to be cooked again before consuming. For the
shrinkage, the water reduction causes the collapse of
structure resulting in the changes of sample dimensions.
In this study, though the drying time was different, there
was a similar amount of water loss during drying with a
slow drying rate. The great change of shrinkage was
found in fast drying as reported by Sa-adchom et al. [14].
Table 2 shows the color values of dried pork by
greenhouse and open sun drying. The color of dried pork
from the greenhouse drying in the afternoon was more
red (a) than that in the morning and open sun drying.
This might be because the accumulated heat in
greenhouse in the morning until in the afternoon resulted
in the high temperature leading to the high a value. This
is involved with the non-enzymatic browning reaction
which is accelerated by several factors such as time,
temperature, pH, water activity and high pressure [13].
From this experiment, the temperature plays an important
role on the high a value.
TABLE
I
H
ARDNESS AND
S
HRINKAGE OF
D
RIED
P
ORK BY
G
REENHOUSE
D
RYER
AND
O
PEN
S
UN
D
RYING
Drying Conditions
Hardness
ns
(N)
Shrinkage
ns
(%)
Open Sun on
24/10/10
2.59 ± 1.05
45 ± 3
Greenhouse Dryer on
24/10/10 (morning)
2.64 ± 1.08
45 ± 2
Greenhouse Dryer on
24/10/10 (afternoon)
2.56 ± 1.14
42 ± 2
ns = not significantly different (p>0.05) by DMRT
TABLE
II
C
OLOR
V
ALUES OF
D
RIED
P
ORK BY
G
REENHOUSE
D
RYER AND
O
PEN
S
UN
D
RYING
Drying Conditions
Color Values
L
ns
a
b
ns
Open Sun on
24/10/10
28.37±0.99
15.21±0.84
b
11.84±0.84
Greenhouse Dryer on
24/10/10 (morning)
28.01±0.93
14.72±1.47
b
11.78±0.99
Greenhouse Dryer on
24/10/10 (afternoon)
28.64±1.16
16.38±0.96
a
11.65±1.08
ns = not significantly different (p>0.05) by DMRT
Means with the same letter within a column are not significantly
different (p>0.05) by DMRT
IV. C
ONCLUSIONS
In this work, the direct solar drying of pork was
characterized using a greenhouse dryer under the climate
conditions of Kalasin, Thailand. The loading capacity of
the dryer is 40 kg of pork. The moisture content was
reduced from 210% db to 70% db in 280 min, whereas
the open sun drying took only 340 min. Most physical
properties of dried pork by greenhouse drying and open
6
8
10
12
14
16
18
400 500 600 700 800 900 1000 1100
Temperature Rise (
๐
C)
GT (W/m2)
Temperature
…
Linear
0.0
50.0
100.0
150.0
200.0
250.0
0 60 120 180 240 300 360 420
Moisture content (% db)
Elapsed drying time (h)
Open sun
