THERMO-PHYSICAL PROPERTIES OF MUSHROOM

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 – 0.354JSM^OC with Auricularia pohytricha having the highest value of 0.354JsmoC and cantharellus cibarius having the lowest value of 0.088 Jsm^oC. 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/kg^oC with cantharellus cibarius having highest value of 0.385kJ/kg^oC and Auricularia polytricha having the lowest value of 0.262KJ/kg^oC. 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/kg^oC)	Thermal conductivity (Jsm^oC)	Thermal diffusivity (x10^-7m²S^-1)
A	1.044^a+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/kg^oC to 0.385kJ/kg^oC with cantherellus cibarius having the highest value of 0.385KJ/kg^oC while Auricularia polytricha having the lowest value of 0.262KJ/kg^oC. 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 0.088Jsm^oC to 0.354Jsm^oC. Cantherellus cibarius had the lowest values (0.088Jsm^oC) while Auricularia polytricha had the highest thermal conductivity values (0.354Jsm^oC). It was observed that the values were low compared to the thermal conductivity of pure water (0.563Jsm^oC), 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 0.563Js^oC, 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 = I

V ________ (ii)

Where

I = Electric current

V = potential difference between the and of the conductor