CHEMICAL COMPOSITION AND BIOACTIVE PROPERTIES OF WATERMELON (Citrullus lanatus) SEED AND ITS APPLICATION IN COOKIE PRODUCTION

Abstract

Watermelon (Citrullus lanatus) seeds were obtained manually from fresh fruit purchased from the local market. The seeds were washed of adhering residue and dried at 45 oC in an oven for 1 h. Three samples were prepared; unbroken seed (whole seed), dehulled seed and the hull separated from the dehulled seed. The three samples were milled into flour and subjected to further analyses, which included proximate composition, mineral content, functional properties, phytochemical analysis, antioxidant properties, antimicrobial activities and amino acid composition. Consumer acceptability of cookies produced from watermelon dehulled seed was also accessed. Result of the proximate composition showed that the dehulled seed possessed highest protein content (25.50%), followed by the whole seed (21.62%) and seed hull (5.78%). The fat content of the seed flours ranged from 6.24% to 48.06% and crude fibre from 7.54% to 21.17%. The mineral analysis revealed that watermelon seed contained very high content of calcium (2145.7 mg/100 g to 5674.03 mg/100 g), sodium (939.0 mg/100 g to 2256.7 mg/100 g), magnesium (79.3 mg/100 g to 707.3 mg/100 g) and potassium (137.0 mg/100 g to 918.3 mg/100 g). The functional properties of the flours showed that the bulk densities of the seed flours ranged from 0.79 g/ml to 0.94 g/ml. Water and oil absorption capacities of the flours ranged from 0.50 g/g to 3.43 g/g and 1.34 g/g to 1.85 g/g respectively. The foaming capacity of the flours was highest in the dehulled seed (28.61%). The seed flours were found to be significantly different (p ≤ 0.05) on the basis of phytochemical analyzed which are: alkaloid (3.57% to 16.70%), phytate (371.0 mg/100 g to 1689 mg/100 g), saponin (12455.0 mg/100 g to 14000 mg/100 g), oxalate (45.0 mg/100 g to 77.0 mg/100 g), tannin (2.20 mg/100 g to 3.57 mg/100 g) and trypsin inhibitors (0.94% to 2.01%). The total phenol content (3.51 mg GAE/g-7.11 mg GAE/g) and total flavonoid content (1.10 mg QE/g-3.47 mg QE/g) were highest in the dehulled seed. Ascorbic acid and tocopherol content of the seed flours ranged from 17.5 mg AAE/g to 23.75 mg AAE/g and 7.0 mg TE/g to 11 mg TE/g respectively. Watermelon seed hull flour exhibited the highest ferric reducing power (26.07 mg AAE/g) and 2,2’-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical scavenging activity (0.168 μg TEAC/g). The whole seed flour (63.57%) demonstrated the highest DPPH radical scavenging activity. The levels of essential amino acid except lysine in the dehulled seed flour were higher than the World Health Organization reference pattern. The analysis of the formulated cookies showed that increase in the levels of dehulled watermelon seed flour resulted in increase in the protein content (22.65% to 33.25%) and weight (4.23 g-5.29 g) progressively. However, addition of dehulled watermelon seed resulted in progressive decrease in fat (3.00%-7.50%) and carbohydrate content (57.55%-58.98%). The information generated from this study on the content of the nutritional, functional and active components of watermelon seed can be useful for the effective use of watermelon seed as an ingredient for nutritional supplement and as a functional food.