Various blanching methods and drying temperatures were applied to bell
pepper ( Capiscum annum ) to investigate the effect on its drying
characteristics. Pepper (Capiscum annum) is an abundant and cheap
source of vitamins, minerals and fibre. However, its high moisture
content makes it susceptible to deterioration. The most common method
of preservation is drying but the dried products obtained are of
reduced nutritional qualities. Pretreatment of pepper before drying
improves the quality of the dried pepper and increases its drying rate.
Steam and water blanching as a form of pretreatment has been reported
to increase drying rate and improve the quality of dried products but
there is not much information on other types of oil/water blanching
methods. The effect of blanching (steam, water, palm oil/water and
groundnut oil/water) as a pretreatment on the drying kinetics of bell
pepper dried at temperatures of 50, 60, 70, 80 and 90°C, was
studied. Drying of raw untreated bell pepper was taken as a control.
The results indicate that water removal at the initial stage of the
drying process was highest and there was a rapid decrease as drying
continued until equilibrium was reached at the end of process. The
blanched samples generally had higher drying rates (at p0.05) than the
untreated samples. The values for the drying rate for steam and water
blanched samples were higher (but not at p<0.05) than the drying
rates for samples blanched in oil/water mixtures. The drying rate as
well as effective moisture diffusivity, Deff, increased with increasing
drying temperature. Values of Deff varied from 3.55 x 10-9 m2/s to 2.34
x 10-9 m2/s with the highest being SB (steam blanched) at 80°C and
the lowest UB (unblanched) at 50°C. The drying process took place
mainly in the falling rate period. The activation energies varied from
39.59 to 83.87 kJ/mol, with PB (palm oil/water blanched) samples having
the lowest and UB having the highest Ea value. The lower values for
pretreated samples imply that water movement from the internal regions
is faster in pretreated samples. This suggests that blanching as a
method of pretreatment generally increases water diffusion