Nulu Nansikombi, Unpublished PhD dissertation, Makerere University
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.
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 key during 0 to 3 months, while moisture loss was important at 4 months 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.
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.
Pumpkins for obtention of flour
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.
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.
Response surface methodology, I optimal design was used to optimise drying conditions (time and temperature) for production of flour with high nutritional and nutraceutical value from flesh and seeds of C. pepo L var. fastigata.
Dry samples were tested for ascorbic acid content, total carotenoids, total antioxidant capacity and starch digestibility.
Seeds were also tested for in vitro protein digestibility, trypsin inhibitor activity, alpha tocopherol, beta tocopherol, and alpha tocotrienol.
The predicted optimum conditions for drying were 57 oC; 6.9 hr for the flesh and 60 oC; 3.15 hr for the seeds. All flesh and seeds parameter models were significant (P<0.05) and parameter responses were within the confidence interval of the predicted respective values.
The most influential model terms were; temperature for resistant starch, in vitro protein digestibility, trypsin inhibitor activity, total carotenoids, α-tocopherol, β-tocopherol and α-tocotrienol; quadratic term of temperature and time for ascorbic acid; and drying time for total antioxidant activity of the flesh and temperature for the seeds.
Response surface methodology hence enabled production of C. pepo L var. fastigata flour with maximum nutritional quality and bioactivity from dried flesh (57 oC for 6.9 hr) and seeds (60 oC for 3.15 hr).
Results of this study will form a basis for food technologists to choose the most appropriate drying conditions if maximum nutritional and health benefits are to be realized from dry C. pepo L var. fastigata flesh and seeds.
In order to understand the possible industrial applications of the flesh and seeds of the different pumpkins varieties, physicochemical properties of flours from flesh and seeds of the different pumpkin varieties were studied.
The low final viscosities and high fibre content observed in pumpkin seed flours especially of C. moschata decne make them most suitable for enriching products for example for diets aimed at maintaining a healthy weight, lowering the risk of diabetes and heart disease where reduced calorie intake is desired.
On the other hand, flours from flesh of C. pepo L var. fastigata and C. moschata decne are most suited for formulations where a higher thickening power is preferred.
Fruit composition, storage stability, optimal drying conditions and flour characteristics for selected pumpkin varieties
Nansikombi, N. (2020). Unpublished PhD dissertation, Makerere University, Kampala, Uganda