| dc.description.abstract | The three economically important species of pumpkin namely Cucurbita maxima,
Cucurbita pepo and Cucurbita moschata have many varieties. Pumpkin peel and flesh are key
inter and intra specie distinguishing features but there is dearth of knowledge about the peel and
flesh characteristics and how these relate to postharvest stability of the different varieties.
Pumpkin flesh and seeds greatly contribute to human diet but also promote health through
antioxidant effects hence often dried and powdered to increase their usability. However, no study
has provided optimum drying temperature time combination for optimal nutritional quality and
bioactivity of pumpkin flesh and seeds. This study aimed at understanding fruit characteristics
and how they associate with postharvest stability of the major pumpkin varieties grown in
Uganda, optimising nutritional quality and bioactivity of flours from flesh and seeds and
assessing the suitability of the flours for value addition.
To determine the pumpkin fruit varietal characteristics and how they relate to postharvest
stability, mature fruits of C. maxima duchesne subsp maxima, C. pepo L var. fastigata and C.
moschata decne were stored at ambient conditions (28 oC average temperature and 78% relative
humidity) for 8 months. Cell microscopic structure, intercellular space size, sugars, starch,
cellulose, hemicellulose, lignin, degree of esterification of pectin, polygalacturonase activity, and
cumulative moisture lost were determined monthly.
Factor analysis revealed the major changes affecting postharvest stability in the first 3 months to
be reduction in sucrose, esterification of pectin, starch, hemicellulose and cellulose, with factor
loadings of -0.97, -0.88, -0.87, -0.82 and -0.79, respectively. Moisture loss from the flesh (0.95)
and peel (0.94), and change in size of intercellular spaces (0.93) were major changes from 4 to 7
months, while polygalacturonase activity (0.64) was the major factor from 7 to 8 months.
Sucrose, starch, cellulose and hemicellulose content and degree of esterification of pectin of
different varieties decreased with storage. Glucose and fructose content increased to a maximum
at 4 months and then reduced. Polygalacturonase activity and lignin generally increased with
storage time. Size of intercellular spaces, and cumulative moisture lost from both flesh and peel
increased with storage.
The results suggest that postharvest stability of pumpkins is determined by an interplay of
factors. The deterministic factor was found to change with storage time. Sucrose breakdown was xvii
key during 0 to 3 months, while moisture loss was important at 4 months of storage.
Polygalacturonase activity became paramount from 7th month of storage. Of all the varieties
studied, C. moschata decne deteriorated fastest. In the first 3 months of storage, the rate of starch
breakdown was 0.45, 0.52 and 0.84 g/100 g/month FW in C. maxima duchesne subsp maxima, C.
pepo L var. fastigata and C. moschata decne, respectively. The pumpkin varieties also showed a
breakdown in sucrose of 0.51, 0.22 and 0.38 g/100 g/month FW respectively, in the first 5
months of storage. C. moschata decne also had the least starch (3.56 g/100 g FW), sucrose (3.15
g/100 g FW), and hemicellulose (1.60 g/100 g FW) contents compared to other varieties.
Pumpkin varieties with more lignified peel had lower rates of sucrose breakdown and moisture
loss and tended to be more stable postharvest. Varieties with low level of hemicellulose had their
cell walls degrade early, while deterioration of pumpkins with highly esterified pectin and
closely packed cells was delayed.
To select a pumpkin variety to be used in optimisation of drying conditions for maximum
nutritional quality and bioactivity of flour from pumpkin flesh and seeds, flesh and seeds of
mature C. maxima duchesne subsp maxima, C. pepo L var. fastigata and C. moschata decne,
were assayed for proximate composition, α, β, γ, δ-tocopherols and tocotrieonols, total
carotenoids, ascorbic acid content, and antioxidant activity. C. moschata decne flesh and seeds
had significantly higher (p<0.05) antioxidant activity (% DPPH radicals scavenged) of 44.68%
and 53.13%, respectively. Among the three varieties, C. maxima duchesne subsp maxima flesh
and seeds had the least antioxidant activity (% DPPH radicals scavenged) of 41.02% and
50.15%, respectively. Fat content of the flesh (0.17-0.23 g/100 g FW) and seed (15.11-19.23
g/100 g FW) and moisture content of the flesh (86.68-90.08 g/100 g FW) and seed (39.85-44.85
g/100 g FW) render all the matrices oil-in-water systems which favours the activity of non-polar
antioxidants like tocopherols, tocotrienols and carotenoids. Seed matrices being more non polar
favour the activity of polar ascorbic acid unlike flesh matrices. For each variety, β and γ tocopherols existed in same amounts. Hence C. pepo L var. fastigata that was more shelf stable
than C. moschata decne and with antioxidant activity second to C. moschata decne was selected
for optimisation of drying conditions for nutritional quality and nutraceutical value of pumpkin
flesh and seeds. | en_US |
