Abstract
Drying kinetics, of pumpkin fruit slices as influenced by sulphiting, was investigated. Pumpkin fruits, were sulphited at 0, 1.0, 1.5, 2.0 and 2.5% to obtain 4 mm thick (P0, 4; P1, 4; P1.5 4; P2, 4; P2.5, 4 - and 5 mm samples (P0, 5; P1, 5; P1.5, 5; P2, 5; P2.5, 5 respectively). Samples were dried at 60, 65, 70, 75 and 80°C at an air velocity of 1.53 m/s. Drying was carried out to constant moisture. Samples were screened using descriptive sensory evaluation to obtain samples P1, 4 and P2, 5 each dried at 75°C as the best samples for 4 mm and 5 mm respectively. Drying curves, moisture diffusitivity, activation energy, drying time and rehydration capacity were determined. The drying curves obtained showed results for a short constant rate followed by a falling rate period. The effective moisture diffusivity varied from 6.235×10<sup>-11</sup> to 12.808×10<sup>-11</sup>m<sup>2</sup>/s for the 4 mm and 9.046 x 10-11 to 21.330 x 10<sup>-11</sup>m<sup>2</sup>/s for the 5 mm samples. Activation energy obtained for P0, 4; P1, 4; P0, 5 and P2, 5 were 31.342, 32.292, 31.525 and 29.88 kJ/mol. respectively. Sulphiting reduced drying time at 1% level from 16.5 to 15.2 hours for the 4 mm sample and 17.8 to 16.9 hours at 2% level of sulphiting for the 5 mm. Sulphite treatment reduced rehydration capacity significantly at p>0.05. This study implies that the parameter which governed the internal transfer of moisture was moisture diffusion.
Highlights
Cucurbita pepo is known as pumpkin in English, elegede in Yoruba (Nigeria), calbaza, in Mexico and furum in Tiv (Nigeria)
This study aims at investigating the influence of sulphite on the internal moisture transfer mechanism during drying of pumpkin fruit slices, the drying time of fresh slices and reconstitution capacity of the dried pumpkin slices
Influence of sulphite on the drying kinetics of pumpkin revealed that, drying of sulphited pumpkin fruit slices occurred mainly in the falling rate period which is typical of the drying behaviour of food products
Summary
Cucurbita pepo is known as pumpkin in English, elegede in Yoruba (Nigeria), calbaza, in Mexico and furum in Tiv (Nigeria). Cucurbita pepo is a herb grown for its fruits and edible seeds [1]. Pumpkin belongs to the family of cucurbitaceae which includes; cucumbers, melons, squash and gourds [2]. Fruits and seeds of pumpkin are mostly used for culinary and medicinal purposes [4]. In Nigeria, pumpkin (fruit) is commonly consumed fresh. Pumpkin fruit has antioxidant capacities as a result of its carotenoids content. Carotenoids are the natural plant pigments which are responsible for the orange colour of pumpkins. It is considered to be a good source of carotenoids, and a very rich source of carotene [6]. The major caroteneoids in pumpkin fruits include; β-carotene, αcarotene, lutein, lycopene, cryptozanthin and zeazanthin [7].
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