Abstract:
Antioxidants play major role in maintaining good health. Pumpkin (Cucurbita maxima) is
one of the richest sources of β-carotene, a powerful antioxidant. However, the
antioxidant activity of vegetables is influenced by the cooking methods. Therefore, this
study aimed to determine the effect of three cooking methods on the antioxidant
properties of pumpkin. The antioxidant activity was determined in terms of total
flavonoid content (TFC), total phenolic content (TPC), antioxidant capacity and
antioxidant activity [2, 2-Diphenyl-1-picrylhydrazyl (DPPH), radical scavenging activity
expressed as IC50 value]. Fresh pumpkin was cut into small pieces and subjected to
different cooking methods (boiling, microwave cooking and stir-frying) until pumpkin
became tender and palatable. Ethanol (70 %, v/v) was used as the solvent to extract
antioxidants. Results showed that TPC of fresh pumpkin was 9.18±0.05 mg GAE/g DM.
Higher loss of TPC was observed during stir-frying (37.36% loss) than microwave cooking
(10.89% loss) and boiling (6.54% loss). The highest TFC obtained from boiled sample
(5.11±0.91 mg CE/g DM) compared to microwave cooking (2.05±0.03 mg CE/g DM) and
stir-frying (2.72±0.32 mg CE/g DM). Microwave cooking minimally destroyed antioxidant
capacity (53.54±8.02 mg AAE/g DM) than stir-frying and boiling compared to fresh
pumpkin (64.02±3.20 mg AAE/g DM). Fresh pumpkin showed significantly (p<0.05)
lower IC50 (0.54±0.02 mg/mL) than microwave cooked (0.65±0.01 mg/mL) and stir fried
pumpkin (0.66±0.02 mg/mL). Boiled pumpkin showed the lowest DPPH radical
scavenging activity (highest IC50 value; 0.77±0.02 mg/mL). There was a positive but weak
correlation (r= 0.23) between TPC and total antioxidant capacity in fresh and all cooked
samples of pumpkin. The reduction in TPC, antioxidant activity and total antioxidant
capacity of pumpkin could be attributed to the breakdown of some heat labile phenolic
compounds; temperature induced chemical oxidation and the release of oxidative and
hydrolytic enzymes that can destroy the antioxidant compounds. However, boiling of
pumpkin increased the TFC, which could be due to increased level of free flavonols
during boiling. Less loss of antioxidant capacity during microwave cooking than boiling
and stir-frying could be due to less leaching and oxidation of antioxidant
compounds.From this study, it can be concluded that, even though all there cooking
methods studied have significant effect on antioxidant activity of pumpkin, microwave
cooking has less effects on antioxidant activity than boiling and stir-frying.
