3. Results and discussion
3.1 Effects of Pre-treatment and temperature on drying rate
Table 1 shows the drying rates obtained. The analysis shows that the effect of the pre-treatment methods used
was not significant (p<0.05). The result also revealed that the effect of interaction between the pre-treatment
methods and the drying temperatures was not significant. However, the effect of drying temperature on the
drying rate was significant (p<0.05). This shows that temperature is the major factor that affects the drying rate
of agricultural products. The result of Duncan’s New Multiple Range Test (DMRT) shows that there is no significant difference between the mean drying rates at 40 0C and 45 0C. However, the mean drying rates obtained at 45 0C, 50 0C and 55 0C are significantly different (Table 2).
Journal of Biology, Agriculture and Healthcare www.iiste.org ISSN 2224-3208 (Paper) ISSN 2225-093X (Online) Vol 2, No.4, 2012
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3.1.1 Effects of Pre-treatment on the drying rate The drying rate increases generally for all the pre-treatment as the temperature increases. At 40 0C the sugar
treated samples have the least drying rate of 0.8 g/hr the values increases with Salt, Blanched and control (in
ascending order). This shows that the pre-treatment used does not affect the drying rate significantly. In all, the drying rate for control was the highest recorded except at 50 0C when the salted samples have the highest value
of 1.64 g/hr. For the blanched samples a marginal increase of 0.01 g/hr was recorded as the temperature is increased from 40 0C to 45 0C. The sugared and salted samples shows higher increase in value of drying rate at 50 0C and 55 0C than those of blanched and control. This is an indication that salting and sugaring enhances
water movement from the fish head under the drying condition investigated. The blanched samples have the highest drying rate for all the temperatures increasing from 1.0 g/hr at 40 0C to 2.58 g/hr at 55 0C. This is due to the effect of heat treatment of the blanched samples which introduced porosity in the fish muscle as a result of cooking thereby enhancing the release of water from the fish muscles. Jason (1980) found that cooking of fish increased 2.7 times the diffusivity of water in the falling rate period, compared with an uncooked sample. The drying rate for salt treated samples was also greater than the values for that of sugar. This is an indication of the effect of osmosis action of salt in the fish samples leading to free movement of water from the fish. However, it was observed that the drying rate of salted samples was less than that of the control sample at 55 0C which is an indication that at high temperatures salt tends to have a reverse effect on drying rate as pointed out in earlier studies by Kilic, 2009; and Oladele and Adediji, 2008. The fact that sugared samples shows the least value shows that sugar treatment is not a preferred method of pre-treatment in fish drying; it affects the taste of the dried samples. However, values obtained are a reflection that the drying rate of fish is not only affected by nature of fish and moisture content but also by the treatment methods. Generally, the drying rate increases with increase in temperature for all the pre-treatment methods for all the fish parts. However, it should be noted that the blanched samples only show marginal increase in the value of drying rate as the temperature increases from 40 0C to 45 0C. This further stressed the fact that while salting is a good pre-treatment at low temperature blanching shows better effect at high temperatures.
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