Abstract:
The objective of this study was to investigate the effects of pre-drying treatments and solar
tunnel dryer zones on drying characteristics and quality parameters of pumpkin pulp powder.
Pumpkin pulp slices (2 mm, thickness) were pretreated with 1% citric acid solution,2% salt
solution, blanched at 650C water containing 1% salt solution for and untreated, then dried at
three zones of solar tunnel dryer with average temperature ,45.64, 54.62 and 64.970C for zone
I, zone II and zone III respectively. As quality parameters, physical, functional, chemical and
nutritional parameters of dried pumpkin were studied. Pumpkin slice dried at zone III achieved
high drying rate and short time. In addition, salt blanched and citric acid treated also increase
moisture removal. Effective moisture diffusivity at zone I, control (7.63*10-9 m
2
/s) was found to
be lower than that of zone III, citric acid treated (2.34*10-8 m
2
/s). Among the seven thin layer
drying models tested, the diffusion approximation, was found best fitting whereas the
logarithmic, two term exponential and Henderson and Babis were found to be suitable models
to describe the drying behavior of pumpkin slice. The highest bulk density value was recorded
at zone III for salt blanched sample and lowest is at zone II for control,0.78±0.02 (g/ml) and
0.52±0.006(g/ml), respectively. Pumpkin which dried at zone III with salt blanched treatment
exhibited high values of water hydration capacity, shrinkage ratio, rehydration ratio and low
water activity. Chemical parameters such as; titrable acidity, pH and total soluble solid was
found between ;2.7±0.01%-1.1±0.003%, 6.1±0.01-4.6±0.007, 11.3±0.04-7.6±0.3 respectively.
Some proximate composition of the pumpkin powder values recorded as follow 8.2±0.03 to
6.4±0.04% moisture content, 6.2±0.006 to4.7±0.02% total ash 4.2±0.05 to 1.1±0.03% fat and
4.2±0.05 to 2.4±0.02% protein. The highest total phenolic content, beta carotene, Ascorbic acid
and antioxidant activity were recorded for sample dried at zone II and treated with 2% salt
solution. Overall, Pumpkin dried at zone III combined and salt blanched, experienced high
moisture removal, short drying time and high effective moisture diffusivity that lead to high
shrinkage ratio, rehydration ratio, bulk density and water absorption capacity where only high
shrinkage ratio is undesirable. Whereas, Pumpkin dried at zone II and salt treated exhibited
better retention of bioactive components.
