Bioactive compounds and antioxidant activities during fruit ripening of watermelon cultivars

Changes in bioactive compounds and antioxidant activities of three commercial selections (Crimson sweet, Dumara and Giza) and two new selections (P503 and P403) of watermelon cultivars were investigated at four different fruit ripening stages (white, white-pink, pink and red-ripe). Lipophilic and hydrophilic antioxidant activities (LAA and HAA, respectively) were determined, and their correlations with total vitamin C, phenol, flavonoid, lycopene and β-carotene contents were studied. Ripening stage significantly influenced lycopene and β-carotene contents, as well as the LAA of all investigated watermelon cultivars. Good correlations between LAA and lycopene and β-carotene contents were found using the TEAC assay. At the red-ripe stage of ripeness, P503 cultivar showed the highest amount of lycopene (64.5 mg kg−1 fw), whereas Dumara cultivar showed the highest level of β-carotene (2.1 mg kg−1 fw). Giza cultivar scored first for total phenol (260.1 mg GAE kg−1 fw), flavonoid (260.0 mg RE kg−1 fw) and total vitamin C (204.0 mg kg−1 fw) contents. Although, the HAA of the studied watermelon cultivars was significantly influenced by the ripening stages, it only correlated to the amount of total phenols and flavonoids. These data confirm the important role played by genetic background and ripening stage in determining antioxidant potential of watermelon fruits. They also give valuable insights into the synthesis and accumulation of bioactive compounds in such fruits, and furthermore move us closer to identifying the harvesting period with the highest antioxidant potential.