Physical Properties Of Western Sudan Watermelon (Citrullus Vulgaris) And Watermelon Seeds

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Mohammed, Nuha Hussein Ibrahim
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This study was conducted to determine the physical properties of Western Sudan watermelon (Citrullus vulgaris) and watermelon seeds to be used in the design of a machine to harvest and separate watermelon seeds from the pulp. The samples were selected from the 2003/04 and 2004/05 growing seasons. The actual volume of watermelon was determined by water displacement method and then the watermelon density and specific gravity were determined. The three axial diameters were measured using an overhead projector. The relationship between the actual volume and the measured dimensions was determined to verify that the estimated volume may be used as a criterion to decide that if these dimensions were sufficient to define watermelon form. The shape of Western Sudan watermelon was resembled by sphere, oblate spheroid and prolate spheroid. The predicted watermelon volumes using the three geometric shapes models were related to the actual volumes. The actual watermelon surface area was determined using a digital planimeter then the rind thickness was measured using a vernier caliper. The predicted surface areas using the three geometric shapes were related to the actual surface areas. The actual watermelon surface area was related to its weight and volume by assuming a linear and non-linear regression models. The predicted surface areas using these two models were related to the actual surface areas. The initial moisture content of watermelon seeds was determined using an air oven method. Then the specific gravity of watermelon seeds was determined using the method of pycnometer and toluene. The weight of 100 seeds, the percentage of red and brown seeds and the percentage of large seeds were recorded to be used in grading the watermelon seeds. The oil content of each watermelon seed variety was found using a soxhelt extracting apparatus. The results showed that both the watermelon density and specific gravity were 0.876 g/cc and 0.892, respectively. The estimated watermelon volume can be used as adequate criterion then the measurement of three axial dimensions, gave a complete theoretical specification of the watermelon shape and size. The oblate spheroid model was found to be more accurate in predicting the volume and surface area of Western Sudan watermelon compared to the sphere and the prolate spheroid models. This suggested that the watermelon shape can be described by an oblate spheroid. The average rind thickness of watermelon was 0.37 mm. Linear regression models were developed to correlate the watermelon surface area with both its weight and volume. It was found that there was strong correlation between the watermelon surface area and its volume than with its weight. Also it was found that the oblate spheroid model was the most accurate predictor of the watermelon surface area among the models tested. The average initial moisture content of the watermelon seeds dried at 105±1°C for 48 hrs was 38.2% (moisture, w. b.). Based on this moisture content, the average specific gravity of the watermelon seeds was 1.016. The watermelon seeds involved in this study were graded as Super Casheir, Casheir, Normal White and Farrasha – third. The watermelon seeds yield a valuable amount of oil ranged from 20.05 to 24.05%.
Western Sudan watermelon; physical properties; criterion