Chemical composition of indiginous of watermelon (Citrullus lanatus Tthunb) Matsum. and Nakai)) landrace seeds from the Sekhukhune and Capricorn District in the Limpopo Province

Abstract

The aim of this study was to investigate the chemical composition of indigenous watermelon landraces (Citrullus lanatus) seeds grown in two districts in the Limpopo Province. Watermelon seeds are the most undermined oilseeds. The seeds have nutritional values that compare favourably with those of soybean, sunflower and ground nuts. Many cucurbit seeds such as watermelon seeds are rich in protein and oil, although none of these products have been used on an industrial scale. Nine indigenous watermelon landraces seeds (four from the Sekhukhune district and five from the Capricorn district) were examined. The landrace 06CDGM was found to have the highest mass per one hundred seeds (10.95 g per 100 seeds) with 07CDGM having the lowest mass (8.05 g per 100 seeds). The landrace 10CDGM was found to have the highest oil (41.5%), protein (20.39%) and fibre content (23.98%) with 01SDPW having the lowest oil yield (30.00%), 02SDPW was found to have the highest saponification value (184.57 mg KOH/g oil) and 09CDGM had the highest iodine value (138.575 g I2/100 g oil). The landrace 01SDPW had the highest total sugar content. All landraces were found to have the essential amino acid leucine. Antioxidant activity (66.95%) and total flavonoids (0.295 mg/g as catechin equivalents) were found to be highest in the 09CDGM landrace, and total phenolic content (0.91 mg/g gallic acid equivalent) was found to be highest in 05SDPW. The landrace 06CDGM was found to have the highest copper content (0.088 mg/g); 02SDPW was found to have the highest iron content (0.194 mg/g); 10CDGM had the highest zinc (0.312 mg/g) and sulphate content (0.129 mg/g); while both 10CDGM and 03SDPW had the highest content of calcium (9.13 mg/g). The landraces were found to differ slightly in the content and quality of components tested. Each of the landraces was found to have some qualities that render them superior to the other landraces. The qualities and content of the landraces compare favourably with those of commercial oil seeds such as the sunflower and soybean. Overall, the landraces from the Capricorn district were observed to have superior qualities than those from the Sekhukhune district. The findings indicated that the landraces from Capricorn district had more mean oil, mean protein, crude fibre content, total phenolics and total flavonoid content than those from the Sekhukhune district. The landraces from Sekhukhune district had high carbohydrate, ash content and high content of the minerals iron and calcium. The landrace 10CDGM was found to have overall high vi values with regard to most analyses, thus making the landrace superior to the others. The results indicate that landraces from both districts have complementary qualities to each other; however the landraces from the Capricorn are more superior in most aspects. The watermelon seeds have the potential to be used as a cost-effective and easily accessible source of nutrients and oil to meet nutritional challenges in developing countries. KEY CONCEPTS Citrullus lanatus; Landrace; Sekhukhune district; Capricorn district; Indigenous watermelon; Oil seeds; Essential amino acids; Antioxidant activity; Total phenolics; Total flavonoids; Mineral content; Total sugars; Crude fibre; Oil content; Saponification value; Iodine value.