Preparation of starch derivatives bearing urea groups and the evaluation of antioxidant, antifungal, and antibacterial activities.

Several starch derivatives bearing urea groups (TUCAST, MTUCAST, and PTUCAST) based on 6-O-chloroacetylated starch (CAST) were successfully designed and synthesized. FT-IR, 1H NMR spectroscopy, and elemental analysis were carried out to identify the structural characteristics of starch derivatives. The antioxidant activity of starch derivatives was tested by superoxide-radical scavenging and hydroxyl-radical scavenging assays. Their antifungal activity against Fusarium oxysporum f. sp. cucumebrium Owen, Phomopsis asparagus, and Fusarium oxysporum f. sp. niveum was estimated by hyphal measurement. Furthermore, the antibacterial activity against Escherichia coli and Staphylococcus aureus was evaluated by optical density method. Compared to starch, the products bearing urea groups showed enhanced antifungal action as well as an excellent antioxidant and antibacterial activities. Their bioactivities decreased roughly in the order of PTUCAST > MTUCAST > TUCAST > CAST > starch, which matched with the electron-withdrawing property of the different substituted groups of urea. Besides, the cytotoxic activity of starch and synthesized derivatives against L929 cells was evaluated using CCK-8 assay in vitro and all samples showed weak cytotoxicity. The results suggested that these novel starch derivatives possessing satisfactory bioactivities could be widely used in the food industry.