ABSTRACT
The thermo-physical properties of
mushroom varieties were determined. The properties evaluated include density,
moisture content, thermal conductivity, thermal diffusivity and specific heat
capacity. The purpose of this study was thus to provide information on the
thermal properties of mushroom varieties to aid in the design and manufacture
of equipment for processing, handing and transportation. The moisture content
ranged from 45.25 -86.00%.
The bulk density was measured and found to be in a
range of 0.0853 - 1.044kgm3 with cantharellus cibarius having the
highest value of 1.044kgm3 and pleurotus ostreatus having the lowest
value of 0.853kg3. The thermal conductivity varied from 0.088 – 0.354JSMOC
with Auricularia pohytricha having the highest value of 0.354JsmoC and
cantharellus cibarius having the lowest value of 0.088 JsmoC. The
thermal diffusivity ranged from 0.219 – 1.4277x10-7 m2S-1
with Auricularia pohytricha having the highest values of 1.427x10-7m2S-1
and cantharellus cibarius having the lowest value of 0.219x10-7m2S-1.
The specific heat capacity ranged from 0.262 – 0.385kJ/kgoC with
cantharellus cibarius having highest value of 0.385kJ/kgoC and
Auricularia polytricha having the lowest value of 0.262KJ/kgoC. Specific
heat capacity, thermal conductivity and thermal diffusivity were found to increase
with increase in moisture content. The results translate that a lot of energy
will be required to heat or cool these sample this implies that they are poor
conductors of heat.
CHAPTER
FOUR
RESULT
AND DISCUSSION
Table 1: The thermo-physical properties
determination of some mushroom varieties.
Sample
|
Density
(kglm3)
|
Specific
heat capacity (kJ/kgoC)
|
Thermal
conductivity (JsmoC)
|
Thermal
diffusivity (x10-7m2S-1)
|
A
|
1.044a+1.000
|
0.385 a+0.001
|
0.088 d+0.010
|
0.219 ad+0.010
|
B
|
0.950 a+0.010
|
0.262 c+0.0100
|
0.354 a+0.010
|
1.422 a+0.010
|
C
|
0.853 a+0.100
|
0.302 b+0.010
|
0.118 c+0.010
|
0.459 c+0.010
|
D
|
0.950 a+0.010
|
0.311 b+0.010
|
0.177 b+0.00
|
0.6 b+0.010
|
Values are means of triplicate
determination.
Values in the same column with the same
superscript are not significantly different (p<0.05)
NOTE: SAMPLE
A is
Cantherellus cibarius
SAMPLE
B is Auricularia polyricha
SAMPLE
C is Pleurotus ostreatus
SAMPLE
D is Phylloponus rhodoxanthus
4.0 DISCUSSION
4.1 PHYSICAL PROPERTY
4.1.1 BULK DENSITY.
The result of
the thermo-physical of mushroom varieties are presented in Table1.The bulk
density of mushroom was found to be in a range of 0.853 – 1.044kg/m3. Pleurotus ostreatus recording the lowest density 0.853kgm3, while canterelles cibarius had the highest
density 1.044kgm3. The densities of the samples investigated in this
work are not significantly different from p<0.05.
These sample had
densities that are lower than that of water, this suggests that these samples
will float in water. This characteristic can be exploited in separation
technique. Hence mushroom with such low densities can be transported by water
or separated from undesirable material in water (Maack, 1959). The lower the
density, the higher the flotation of the samples on top of water and as a
result may not be of a high quality and may in turn be rejected by consumers.
Nwanekezi and Ukagu (1999) found that density as an engineering property is
used for quality assessment especially during separation of intact quality
fruits and vegetables. Maturity evaluation and quality of a particular food
material can be determined by it’s density (Lee, 1948). Density as an
engineering property involves the transfer of heat.
4.2 THERMAL PROPERTIES
4.2.1 SPECIFIC HEAT CAPACITY
There was no
significant difference (p<0.05) in the specific heat capacity of pleurotus
ostreatus and phylloponus rhodoxanthus analyzed but cantherellus cibarius and
Auricularia polytricha were significant difference. The specific heat capacity
ranged from 0.262kJ/kgoC to 0.385kJ/kgoC with
cantherellus cibarius having the highest value of 0.385KJ/kgoC while
Auricularia polytricha having the lowest value of 0.262KJ/kgoC. It
was also observed that the specific heat capacity of the samples were found to
be low, this implies that low energy will be required to heat or cool these
mushrooms and once heated or cooled, they retain their temperature for a period
of time. Although specific heat capacity is a function of temperature, its
variation is not as significant as that of gases, the value however for any
food material, depend on a large extent on its composition (Onwuka, 2003).
Specific heat capacity of fatty foods is low. Specific heat capacity is defined
as the quantity of heat gained or lost by unit mass of fruits and vegetables to
accomplish unit change in temperature.
4.2.2 THERMAL CONDUCTIVITY
The
thermal conductivity of the mushroom samples ranged from 0.088JsmoC
to 0.354JsmoC. Cantherellus cibarius had the lowest values (0.088JsmoC)
while Auricularia polytricha had the highest thermal conductivity values
(0.354JsmoC). It was observed that the values were low compared to
the thermal conductivity of pure water (0.563JsmoC), this may be due
to the total solid in the mushroom samples, this implies that they are poor
conductors of heat, also the heat energy diffusion on transfer through these
mushroom during drying, freezing and evaporation are likely to be very slow
(Ikegwu and Ekwu, 2009). Most agricultural materials are made up primarily of
the solid and the water component and thus most thermal conductivity expression
in corporate the percentage water content to emphasize significant increase in
the overall value during a phase change. Nwanekezi and Ukagu (1999) reported that
good conductors like metals have high thermal conductivity and low specific
heat capacity value. From the statistical analysis carried out. It was observed
that all samples were significant different at p<0.05
4.4.3 THERMAL DIFFUSIVITY
A thermal diffusivity quantity is a
material ability to conduct heat relative to its ability to store heat. (Martens
1980). If density of a material and specific heat are held constant, the
thermal diffusivity and the rate of heat
transfer will increase as thermal conductivity increases, conversely increase
in density and the amount of heat stored for a constant thermal conductivity
will decrease the rate of heat transfer. (choi and okos (1986).
The thermal diffusivity of the
mushroom samples ranged from 0.219x10-7m2S to 1.427x10-7m2
with Auricularia polytricha having the
highest value of 1.42x10-7m2S while cantharellus cibarius had the lowest value of 0.219x10-7m2S.
It was also observed that cantharellus cibarius and Auricularia pohytricha was
not significantly different and the other two samples were significantly
different at p<0.05. This implies that the low thermal diffusivities of
these mushroom may probably explain their low conductivitus. Therefore movement
or diffusion of that energy from one point to another in these foods would
generally be very low during thermal processing.
CHAPTER FIVE
The result of
this research revealed that the mushroom cantharellus cibarius and phylloponus
rhodoxanthus were of high moisture content 86% and 62.25% respectively. Thus
supporting the growth of micro organism when stored at ambient temperature
hence these product are of high perishability. Therefore in order to preserve these
food their moisture content have to be reduced to the level that will make moisture
unavailable for microbial growth. The results revealed that the values of
thermal conductivities and diffusivities of the mushroom varieties were low compared
to pure water of 0.563JsoC, this implies that they are poor
conductors of heat. The densities of the mushroom varieties were also low
compared to that of water. There was no significant difference in density but
significant different in thermal conductivity. It was also observed that the
samples with high specific heat capacity also had high moisture content. These
samples will not require longer time to be heat processed to a specific level
in a processing system operating at a specific temperature.
I wish to
recommend that more work should be done on the thermal and physical properties of other edible mushroom as we have seen the
importance of mushroom to human can hot be over emphasized.
APPENDX II
Determination of Q, from Q =
I2 R
Q = I2 R = QT
4II (T1 – T2)
=
R = I V
I = V R = (v =
IR)_______ (i)
V = I
R
R = I
V ________
(ii)
Where
I = Electric
current
V
= potential difference between the
and of the conductor
R = Resistance
Q = Rate
of heat flow.
Thermal conductivity
Evaluation
Q = I2R
.
Taking
,
I = 5A
V = 28V
I = V R
5 = 28XR
28 = 5/R
R = 5/28 = 0.178. M
I2R = 52
X 0.1.78
Q = 4.45J.